mncheck/mncheck/ext/path.py

#
# Copyright (c) 2010 Mikhail Gusarov
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
#

"""
path.py - An object representing a path to a file or directory.

https://github.com/jaraco/path.py

Example::

    from path import Path
    d = Path('/home/guido/bin')

    # Globbing
    for f in d.files('*.py'):
        f.chmod(0o755)

    # Changing the working directory:
    with Path("somewhere"):
        # cwd in now `somewhere`
        ...

    # Concatenate paths with /
    foo_txt = Path("bar") / "foo.txt"
"""

from __future__ import unicode_literals

import sys
import warnings
import os
import fnmatch
import glob
import shutil
import hashlib
import errno
import tempfile
import functools
import operator
import re
import contextlib
import io
import distutils.dir_util
import importlib
import itertools

try:
    import win32security
except ImportError:
    pass

try:
    import pwd
except ImportError:
    pass

try:
    import grp
except ImportError:
    pass

##############################################################################
# Python 2/3 support
PY3 = sys.version_info >= (3,)
PY2 = not PY3

string_types = str,
text_type = str
getcwdu = os.getcwd


if PY2:
    import __builtin__
    string_types = __builtin__.basestring,
    text_type = __builtin__.unicode
    getcwdu = os.getcwdu
    map = itertools.imap


@contextlib.contextmanager
def io_error_compat():
    try:
        yield
    except IOError as io_err:
        # On Python 2, io.open raises IOError; transform to OSError for
        # future compatibility.
        os_err = OSError(*io_err.args)
        os_err.filename = getattr(io_err, 'filename', None)
        raise os_err

##############################################################################


__all__ = ['Path', 'TempDir', 'CaseInsensitivePattern']


LINESEPS = ['\r\n', '\r', '\n']
U_LINESEPS = LINESEPS + ['\u0085', '\u2028', '\u2029']
NEWLINE = re.compile('|'.join(LINESEPS))
U_NEWLINE = re.compile('|'.join(U_LINESEPS))
NL_END = re.compile(r'(?:{0})$'.format(NEWLINE.pattern))
U_NL_END = re.compile(r'(?:{0})$'.format(U_NEWLINE.pattern))


try:
    import pkg_resources
    __version__ = pkg_resources.require('path.py')[0].version
except Exception:
    __version__ = 'unknown'


class TreeWalkWarning(Warning):
    pass


# from jaraco.functools
def compose(*funcs):
    compose_two = lambda f1, f2: lambda *args, **kwargs: f1(f2(*args, **kwargs))  # noqa
    return functools.reduce(compose_two, funcs)


def simple_cache(func):
    """
    Save results for the :meth:'path.using_module' classmethod.
    When Python 3.2 is available, use functools.lru_cache instead.
    """
    saved_results = {}

    def wrapper(cls, module):
        if module in saved_results:
            return saved_results[module]
        saved_results[module] = func(cls, module)
        return saved_results[module]
    return wrapper


class ClassProperty(property):
    def __get__(self, cls, owner):
        return self.fget.__get__(None, owner)()


class multimethod(object):
    """
    Acts like a classmethod when invoked from the class and like an
    instancemethod when invoked from the instance.
    """
    def __init__(self, func):
        self.func = func

    def __get__(self, instance, owner):
        return (
            functools.partial(self.func, owner) if instance is None
            else functools.partial(self.func, owner, instance)
        )


class Path(text_type):
    """
    Represents a filesystem path.

    For documentation on individual methods, consult their
    counterparts in :mod:`os.path`.

    Some methods are additionally included from :mod:`shutil`.
    The functions are linked directly into the class namespace
    such that they will be bound to the Path instance. For example,
    ``Path(src).copy(target)`` is equivalent to
    ``shutil.copy(src, target)``. Therefore, when referencing
    the docs for these methods, assume `src` references `self`,
    the Path instance.
    """

    module = os.path
    """ The path module to use for path operations.

    .. seealso:: :mod:`os.path`
    """

    def __init__(self, other=''):
        if other is None:
            raise TypeError("Invalid initial value for path: None")

    @classmethod
    @simple_cache
    def using_module(cls, module):
        subclass_name = cls.__name__ + '_' + module.__name__
        if PY2:
            subclass_name = str(subclass_name)
        bases = (cls,)
        ns = {'module': module}
        return type(subclass_name, bases, ns)

    @ClassProperty
    @classmethod
    def _next_class(cls):
        """
        What class should be used to construct new instances from this class
        """
        return cls

    # --- Special Python methods.

    def __repr__(self):
        return '%s(%s)' % (type(self).__name__, super(Path, self).__repr__())

    # Adding a Path and a string yields a Path.
    def __add__(self, more):
        try:
            return self._next_class(super(Path, self).__add__(more))
        except TypeError:  # Python bug
            return NotImplemented

    def __radd__(self, other):
        if not isinstance(other, string_types):
            return NotImplemented
        return self._next_class(other.__add__(self))

    # The / operator joins Paths.
    def __div__(self, rel):
        """ fp.__div__(rel) == fp / rel == fp.joinpath(rel)

        Join two path components, adding a separator character if
        needed.

        .. seealso:: :func:`os.path.join`
        """
        return self._next_class(self.module.join(self, rel))

    # Make the / operator work even when true division is enabled.
    __truediv__ = __div__

    # The / operator joins Paths the other way around
    def __rdiv__(self, rel):
        """ fp.__rdiv__(rel) == rel / fp

        Join two path components, adding a separator character if
        needed.

        .. seealso:: :func:`os.path.join`
        """
        return self._next_class(self.module.join(rel, self))

    # Make the / operator work even when true division is enabled.
    __rtruediv__ = __rdiv__

    def __enter__(self):
        self._old_dir = self.getcwd()
        os.chdir(self)
        return self

    def __exit__(self, *_):
        os.chdir(self._old_dir)

    def __fspath__(self):
        return self

    @classmethod
    def getcwd(cls):
        """ Return the current working directory as a path object.

        .. seealso:: :func:`os.getcwdu`
        """
        return cls(getcwdu())

    #
    # --- Operations on Path strings.

    def abspath(self):
        """ .. seealso:: :func:`os.path.abspath` """
        return self._next_class(self.module.abspath(self))

    def normcase(self):
        """ .. seealso:: :func:`os.path.normcase` """
        return self._next_class(self.module.normcase(self))

    def normpath(self):
        """ .. seealso:: :func:`os.path.normpath` """
        return self._next_class(self.module.normpath(self))

    def realpath(self):
        """ .. seealso:: :func:`os.path.realpath` """
        return self._next_class(self.module.realpath(self))

    def expanduser(self):
        """ .. seealso:: :func:`os.path.expanduser` """
        return self._next_class(self.module.expanduser(self))

    def expandvars(self):
        """ .. seealso:: :func:`os.path.expandvars` """
        return self._next_class(self.module.expandvars(self))

    def dirname(self):
        """ .. seealso:: :attr:`parent`, :func:`os.path.dirname` """
        return self._next_class(self.module.dirname(self))

    def basename(self):
        """ .. seealso:: :attr:`name`, :func:`os.path.basename` """
        return self._next_class(self.module.basename(self))

    def expand(self):
        """ Clean up a filename by calling :meth:`expandvars()`,
        :meth:`expanduser()`, and :meth:`normpath()` on it.

        This is commonly everything needed to clean up a filename
        read from a configuration file, for example.
        """
        return self.expandvars().expanduser().normpath()

    @property
    def stem(self):
        """ The same as :meth:`name`, but with one file extension stripped off.

        >>> Path('/home/guido/python.tar.gz').stem
        'python.tar'
        """
        base, ext = self.module.splitext(self.name)
        return base

    @property
    def namebase(self):
        warnings.warn("Use .stem instead of .namebase", DeprecationWarning)
        return self.stem

    @property
    def ext(self):
        """ The file extension, for example ``'.py'``. """
        f, ext = self.module.splitext(self)
        return ext

    def with_suffix(self, suffix):
        """ Return a new path with the file suffix changed (or added, if none)

        >>> Path('/home/guido/python.tar.gz').with_suffix(".foo")
        Path('/home/guido/python.tar.foo')

        >>> Path('python').with_suffix('.zip')
        Path('python.zip')

        >>> Path('filename.ext').with_suffix('zip')
        Traceback (most recent call last):
        ...
        ValueError: Invalid suffix 'zip'
        """
        if not suffix.startswith('.'):
            raise ValueError("Invalid suffix {suffix!r}".format(**locals()))

        return self.stripext() + suffix

    @property
    def drive(self):
        """ The drive specifier, for example ``'C:'``.

        This is always empty on systems that don't use drive specifiers.
        """
        drive, r = self.module.splitdrive(self)
        return self._next_class(drive)

    parent = property(
        dirname, None, None,
        """ This path's parent directory, as a new Path object.

        For example,
        ``Path('/usr/local/lib/libpython.so').parent ==
        Path('/usr/local/lib')``

        .. seealso:: :meth:`dirname`, :func:`os.path.dirname`
        """)

    name = property(
        basename, None, None,
        """ The name of this file or directory without the full path.

        For example,
        ``Path('/usr/local/lib/libpython.so').name == 'libpython.so'``

        .. seealso:: :meth:`basename`, :func:`os.path.basename`
        """)

    def splitpath(self):
        """ p.splitpath() -> Return ``(p.parent, p.name)``.

        .. seealso:: :attr:`parent`, :attr:`name`, :func:`os.path.split`
        """
        parent, child = self.module.split(self)
        return self._next_class(parent), child

    def splitdrive(self):
        """ p.splitdrive() -> Return ``(p.drive, <the rest of p>)``.

        Split the drive specifier from this path.  If there is
        no drive specifier, :samp:`{p.drive}` is empty, so the return value
        is simply ``(Path(''), p)``.  This is always the case on Unix.

        .. seealso:: :func:`os.path.splitdrive`
        """
        drive, rel = self.module.splitdrive(self)
        return self._next_class(drive), rel

    def splitext(self):
        """ p.splitext() -> Return ``(p.stripext(), p.ext)``.

        Split the filename extension from this path and return
        the two parts.  Either part may be empty.

        The extension is everything from ``'.'`` to the end of the
        last path segment.  This has the property that if
        ``(a, b) == p.splitext()``, then ``a + b == p``.

        .. seealso:: :func:`os.path.splitext`
        """
        filename, ext = self.module.splitext(self)
        return self._next_class(filename), ext

    def stripext(self):
        """ p.stripext() -> Remove one file extension from the path.

        For example, ``Path('/home/guido/python.tar.gz').stripext()``
        returns ``Path('/home/guido/python.tar')``.
        """
        return self.splitext()[0]

    def splitunc(self):
        """ .. seealso:: :func:`os.path.splitunc` """
        unc, rest = self.module.splitunc(self)
        return self._next_class(unc), rest

    @property
    def uncshare(self):
        """
        The UNC mount point for this path.
        This is empty for paths on local drives.
        """
        unc, r = self.module.splitunc(self)
        return self._next_class(unc)

    @multimethod
    def joinpath(cls, first, *others):
        """
        Join first to zero or more :class:`Path` components,
        adding a separator character (:samp:`{first}.module.sep`)
        if needed.  Returns a new instance of
        :samp:`{first}._next_class`.

        .. seealso:: :func:`os.path.join`
        """
        if not isinstance(first, cls):
            first = cls(first)
        return first._next_class(first.module.join(first, *others))

    def splitall(self):
        r""" Return a list of the path components in this path.

        The first item in the list will be a Path.  Its value will be
        either :data:`os.curdir`, :data:`os.pardir`, empty, or the root
        directory of this path (for example, ``'/'`` or ``'C:\\'``).  The
        other items in the list will be strings.

        ``path.Path.joinpath(*result)`` will yield the original path.
        """
        parts = []
        loc = self
        while loc != os.curdir and loc != os.pardir:
            prev = loc
            loc, child = prev.splitpath()
            if loc == prev:
                break
            parts.append(child)
        parts.append(loc)
        parts.reverse()
        return parts

    def relpath(self, start='.'):
        """ Return this path as a relative path,
        based from `start`, which defaults to the current working directory.
        """
        cwd = self._next_class(start)
        return cwd.relpathto(self)

    def relpathto(self, dest):
        """ Return a relative path from `self` to `dest`.

        If there is no relative path from `self` to `dest`, for example if
        they reside on different drives in Windows, then this returns
        ``dest.abspath()``.
        """
        origin = self.abspath()
        dest = self._next_class(dest).abspath()

        orig_list = origin.normcase().splitall()
        # Don't normcase dest!  We want to preserve the case.
        dest_list = dest.splitall()

        if orig_list[0] != self.module.normcase(dest_list[0]):
            # Can't get here from there.
            return dest

        # Find the location where the two paths start to differ.
        i = 0
        for start_seg, dest_seg in zip(orig_list, dest_list):
            if start_seg != self.module.normcase(dest_seg):
                break
            i += 1

        # Now i is the point where the two paths diverge.
        # Need a certain number of "os.pardir"s to work up
        # from the origin to the point of divergence.
        segments = [os.pardir] * (len(orig_list) - i)
        # Need to add the diverging part of dest_list.
        segments += dest_list[i:]
        if len(segments) == 0:
            # If they happen to be identical, use os.curdir.
            relpath = os.curdir
        else:
            relpath = self.module.join(*segments)
        return self._next_class(relpath)

    # --- Listing, searching, walking, and matching

    def listdir(self, pattern=None):
        """ D.listdir() -> List of items in this directory.

        Use :meth:`files` or :meth:`dirs` instead if you want a listing
        of just files or just subdirectories.

        The elements of the list are Path objects.

        With the optional `pattern` argument, this only lists
        items whose names match the given pattern.

        .. seealso:: :meth:`files`, :meth:`dirs`
        """
        if pattern is None:
            pattern = '*'
        return [
            self / child
            for child in os.listdir(self)
            if self._next_class(child).fnmatch(pattern)
        ]

    def dirs(self, pattern=None):
        """ D.dirs() -> List of this directory's subdirectories.

        The elements of the list are Path objects.
        This does not walk recursively into subdirectories
        (but see :meth:`walkdirs`).

        With the optional `pattern` argument, this only lists
        directories whose names match the given pattern.  For
        example, ``d.dirs('build-*')``.
        """
        return [p for p in self.listdir(pattern) if p.isdir()]

    def files(self, pattern=None):
        """ D.files() -> List of the files in this directory.

        The elements of the list are Path objects.
        This does not walk into subdirectories (see :meth:`walkfiles`).

        With the optional `pattern` argument, this only lists files
        whose names match the given pattern.  For example,
        ``d.files('*.pyc')``.
        """

        return [p for p in self.listdir(pattern) if p.isfile()]

    def walk(self, pattern=None, errors='strict'):
        """ D.walk() -> iterator over files and subdirs, recursively.

        The iterator yields Path objects naming each child item of
        this directory and its descendants.  This requires that
        ``D.isdir()``.

        This performs a depth-first traversal of the directory tree.
        Each directory is returned just before all its children.

        The `errors=` keyword argument controls behavior when an
        error occurs.  The default is ``'strict'``, which causes an
        exception.  Other allowed values are ``'warn'`` (which
        reports the error via :func:`warnings.warn()`), and ``'ignore'``.
        `errors` may also be an arbitrary callable taking a msg parameter.
        """
        class Handlers:
            def strict(msg):
                raise

            def warn(msg):
                warnings.warn(msg, TreeWalkWarning)

            def ignore(msg):
                pass

        if not callable(errors) and errors not in vars(Handlers):
            raise ValueError("invalid errors parameter")
        errors = vars(Handlers).get(errors, errors)

        try:
            childList = self.listdir()
        except Exception:
            exc = sys.exc_info()[1]
            tmpl = "Unable to list directory '%(self)s': %(exc)s"
            msg = tmpl % locals()
            errors(msg)
            return

        for child in childList:
            if pattern is None or child.fnmatch(pattern):
                yield child
            try:
                isdir = child.isdir()
            except Exception:
                exc = sys.exc_info()[1]
                tmpl = "Unable to access '%(child)s': %(exc)s"
                msg = tmpl % locals()
                errors(msg)
                isdir = False

            if isdir:
                for item in child.walk(pattern, errors):
                    yield item

    def walkdirs(self, pattern=None, errors='strict'):
        """ D.walkdirs() -> iterator over subdirs, recursively.

        With the optional `pattern` argument, this yields only
        directories whose names match the given pattern.  For
        example, ``mydir.walkdirs('*test')`` yields only directories
        with names ending in ``'test'``.

        The `errors=` keyword argument controls behavior when an
        error occurs.  The default is ``'strict'``, which causes an
        exception.  The other allowed values are ``'warn'`` (which
        reports the error via :func:`warnings.warn()`), and ``'ignore'``.
        """
        if errors not in ('strict', 'warn', 'ignore'):
            raise ValueError("invalid errors parameter")

        try:
            dirs = self.dirs()
        except Exception:
            if errors == 'ignore':
                return
            elif errors == 'warn':
                warnings.warn(
                    "Unable to list directory '%s': %s"
                    % (self, sys.exc_info()[1]),
                    TreeWalkWarning)
                return
            else:
                raise

        for child in dirs:
            if pattern is None or child.fnmatch(pattern):
                yield child
            for subsubdir in child.walkdirs(pattern, errors):
                yield subsubdir

    def walkfiles(self, pattern=None, errors='strict'):
        """ D.walkfiles() -> iterator over files in D, recursively.

        The optional argument `pattern` limits the results to files
        with names that match the pattern.  For example,
        ``mydir.walkfiles('*.tmp')`` yields only files with the ``.tmp``
        extension.
        """
        if errors not in ('strict', 'warn', 'ignore'):
            raise ValueError("invalid errors parameter")

        try:
            childList = self.listdir()
        except Exception:
            if errors == 'ignore':
                return
            elif errors == 'warn':
                warnings.warn(
                    "Unable to list directory '%s': %s"
                    % (self, sys.exc_info()[1]),
                    TreeWalkWarning)
                return
            else:
                raise

        for child in childList:
            try:
                isfile = child.isfile()
                isdir = not isfile and child.isdir()
            except Exception:
                if errors == 'ignore':
                    continue
                elif errors == 'warn':
                    warnings.warn(
                        "Unable to access '%s': %s"
                        % (self, sys.exc_info()[1]),
                        TreeWalkWarning)
                    continue
                else:
                    raise

            if isfile:
                if pattern is None or child.fnmatch(pattern):
                    yield child
            elif isdir:
                for f in child.walkfiles(pattern, errors):
                    yield f

    def fnmatch(self, pattern, normcase=None):
        """ Return ``True`` if `self.name` matches the given `pattern`.

        `pattern` - A filename pattern with wildcards,
            for example ``'*.py'``. If the pattern contains a `normcase`
            attribute, it is applied to the name and path prior to comparison.

        `normcase` - (optional) A function used to normalize the pattern and
            filename before matching. Defaults to :meth:`self.module`, which
            defaults to :meth:`os.path.normcase`.

        .. seealso:: :func:`fnmatch.fnmatch`
        """
        default_normcase = getattr(pattern, 'normcase', self.module.normcase)
        normcase = normcase or default_normcase
        name = normcase(self.name)
        pattern = normcase(pattern)
        return fnmatch.fnmatchcase(name, pattern)

    def glob(self, pattern):
        """ Return a list of Path objects that match the pattern.

        `pattern` - a path relative to this directory, with wildcards.

        For example, ``Path('/users').glob('*/bin/*')`` returns a list
        of all the files users have in their :file:`bin` directories.

        .. seealso:: :func:`glob.glob`

        .. note:: Glob is **not** recursive, even when using ``**``.
                  To do recursive globbing see :func:`walk`,
                  :func:`walkdirs` or :func:`walkfiles`.
        """
        cls = self._next_class
        return [cls(s) for s in glob.glob(self / pattern)]

    def iglob(self, pattern):
        """ Return an iterator of Path objects that match the pattern.

        `pattern` - a path relative to this directory, with wildcards.

        For example, ``Path('/users').iglob('*/bin/*')`` returns an
        iterator of all the files users have in their :file:`bin`
        directories.

        .. seealso:: :func:`glob.iglob`

        .. note:: Glob is **not** recursive, even when using ``**``.
                  To do recursive globbing see :func:`walk`,
                  :func:`walkdirs` or :func:`walkfiles`.
        """
        cls = self._next_class
        return (cls(s) for s in glob.iglob(self / pattern))

    #
    # --- Reading or writing an entire file at once.

    def open(self, *args, **kwargs):
        """ Open this file and return a corresponding :class:`file` object.

        Keyword arguments work as in :func:`io.open`.  If the file cannot be
        opened, an :class:`~exceptions.OSError` is raised.
        """
        with io_error_compat():
            return io.open(self, *args, **kwargs)

    def bytes(self):
        """ Open this file, read all bytes, return them as a string. """
        with self.open('rb') as f:
            return f.read()

    def chunks(self, size, *args, **kwargs):
        """ Returns a generator yielding chunks of the file, so it can
            be read piece by piece with a simple for loop.

           Any argument you pass after `size` will be passed to :meth:`open`.

           :example:

               >>> hash = hashlib.md5()
               >>> for chunk in Path("path.py").chunks(8192, mode='rb'):
               ...     hash.update(chunk)

            This will read the file by chunks of 8192 bytes.
        """
        with self.open(*args, **kwargs) as f:
            for chunk in iter(lambda: f.read(size) or None, None):
                yield chunk

    def write_bytes(self, bytes, append=False):
        """ Open this file and write the given bytes to it.

        Default behavior is to overwrite any existing file.
        Call ``p.write_bytes(bytes, append=True)`` to append instead.
        """
        if append:
            mode = 'ab'
        else:
            mode = 'wb'
        with self.open(mode) as f:
            f.write(bytes)

    def text(self, encoding=None, errors='strict'):
        r""" Open this file, read it in, return the content as a string.

        All newline sequences are converted to ``'\n'``.  Keyword arguments
        will be passed to :meth:`open`.

        .. seealso:: :meth:`lines`
        """
        with self.open(mode='r', encoding=encoding, errors=errors) as f:
            return U_NEWLINE.sub('\n', f.read())

    def write_text(self, text, encoding=None, errors='strict',
                   linesep=os.linesep, append=False):
        r""" Write the given text to this file.

        The default behavior is to overwrite any existing file;
        to append instead, use the `append=True` keyword argument.

        There are two differences between :meth:`write_text` and
        :meth:`write_bytes`: newline handling and Unicode handling.
        See below.

        Parameters:

          `text` - str/unicode - The text to be written.

          `encoding` - str - The Unicode encoding that will be used.
              This is ignored if `text` isn't a Unicode string.

          `errors` - str - How to handle Unicode encoding errors.
              Default is ``'strict'``.  See ``help(unicode.encode)`` for the
              options.  This is ignored if `text` isn't a Unicode
              string.

          `linesep` - keyword argument - str/unicode - The sequence of
              characters to be used to mark end-of-line.  The default is
              :data:`os.linesep`.  You can also specify ``None`` to
              leave all newlines as they are in `text`.

          `append` - keyword argument - bool - Specifies what to do if
              the file already exists (``True``: append to the end of it;
              ``False``: overwrite it.)  The default is ``False``.


        --- Newline handling.

        ``write_text()`` converts all standard end-of-line sequences
        (``'\n'``, ``'\r'``, and ``'\r\n'``) to your platform's default
        end-of-line sequence (see :data:`os.linesep`; on Windows, for example,
        the end-of-line marker is ``'\r\n'``).

        If you don't like your platform's default, you can override it
        using the `linesep=` keyword argument.  If you specifically want
        ``write_text()`` to preserve the newlines as-is, use ``linesep=None``.

        This applies to Unicode text the same as to 8-bit text, except
        there are three additional standard Unicode end-of-line sequences:
        ``u'\x85'``, ``u'\r\x85'``, and ``u'\u2028'``.

        (This is slightly different from when you open a file for
        writing with ``fopen(filename, "w")`` in C or ``open(filename, 'w')``
        in Python.)


        --- Unicode

        If `text` isn't Unicode, then apart from newline handling, the
        bytes are written verbatim to the file.  The `encoding` and
        `errors` arguments are not used and must be omitted.

        If `text` is Unicode, it is first converted to :func:`bytes` using the
        specified `encoding` (or the default encoding if `encoding`
        isn't specified).  The `errors` argument applies only to this
        conversion.

        """
        if isinstance(text, text_type):
            if linesep is not None:
                text = U_NEWLINE.sub(linesep, text)
            text = text.encode(encoding or sys.getdefaultencoding(), errors)
        else:
            assert encoding is None
            text = NEWLINE.sub(linesep, text)
        self.write_bytes(text, append=append)

    def lines(self, encoding=None, errors='strict', retain=True):
        r""" Open this file, read all lines, return them in a list.

        Optional arguments:
            `encoding` - The Unicode encoding (or character set) of
                the file.  The default is ``None``, meaning the content
                of the file is read as 8-bit characters and returned
                as a list of (non-Unicode) str objects.
            `errors` - How to handle Unicode errors; see help(str.decode)
                for the options.  Default is ``'strict'``.
            `retain` - If ``True``, retain newline characters; but all newline
                character combinations (``'\r'``, ``'\n'``, ``'\r\n'``) are
                translated to ``'\n'``.  If ``False``, newline characters are
                stripped off.  Default is ``True``.

        This uses ``'U'`` mode.

        .. seealso:: :meth:`text`
        """
        if encoding is None and retain:
            with self.open('U') as f:
                return f.readlines()
        else:
            return self.text(encoding, errors).splitlines(retain)

    def write_lines(self, lines, encoding=None, errors='strict',
                    linesep=os.linesep, append=False):
        r""" Write the given lines of text to this file.

        By default this overwrites any existing file at this path.

        This puts a platform-specific newline sequence on every line.
        See `linesep` below.

            `lines` - A list of strings.

            `encoding` - A Unicode encoding to use.  This applies only if
                `lines` contains any Unicode strings.

            `errors` - How to handle errors in Unicode encoding.  This
                also applies only to Unicode strings.

            linesep - The desired line-ending.  This line-ending is
                applied to every line.  If a line already has any
                standard line ending (``'\r'``, ``'\n'``, ``'\r\n'``,
                ``u'\x85'``, ``u'\r\x85'``, ``u'\u2028'``), that will
                be stripped off and this will be used instead.  The
                default is os.linesep, which is platform-dependent
                (``'\r\n'`` on Windows, ``'\n'`` on Unix, etc.).
                Specify ``None`` to write the lines as-is, like
                :meth:`file.writelines`.

        Use the keyword argument ``append=True`` to append lines to the
        file.  The default is to overwrite the file.

        .. warning ::

            When you use this with Unicode data, if the encoding of the
            existing data in the file is different from the encoding
            you specify with the `encoding=` parameter, the result is
            mixed-encoding data, which can really confuse someone trying
            to read the file later.
        """
        with self.open('ab' if append else 'wb') as f:
            for line in lines:
                isUnicode = isinstance(line, text_type)
                if linesep is not None:
                    pattern = U_NL_END if isUnicode else NL_END
                    line = pattern.sub('', line) + linesep
                if isUnicode:
                    line = line.encode(
                        encoding or sys.getdefaultencoding(), errors)
                f.write(line)

    def read_md5(self):
        """ Calculate the md5 hash for this file.

        This reads through the entire file.

        .. seealso:: :meth:`read_hash`
        """
        return self.read_hash('md5')

    def _hash(self, hash_name):
        """ Returns a hash object for the file at the current path.

        `hash_name` should be a hash algo name (such as ``'md5'``
        or ``'sha1'``) that's available in the :mod:`hashlib` module.
        """
        m = hashlib.new(hash_name)
        for chunk in self.chunks(8192, mode="rb"):
            m.update(chunk)
        return m

    def read_hash(self, hash_name):
        """ Calculate given hash for this file.

        List of supported hashes can be obtained from :mod:`hashlib` package.
        This reads the entire file.

        .. seealso:: :meth:`hashlib.hash.digest`
        """
        return self._hash(hash_name).digest()

    def read_hexhash(self, hash_name):
        """ Calculate given hash for this file, returning hexdigest.

        List of supported hashes can be obtained from :mod:`hashlib` package.
        This reads the entire file.

        .. seealso:: :meth:`hashlib.hash.hexdigest`
        """
        return self._hash(hash_name).hexdigest()

    # --- Methods for querying the filesystem.
    # N.B. On some platforms, the os.path functions may be implemented in C
    # (e.g. isdir on Windows, Python 3.2.2), and compiled functions don't get
    # bound. Playing it safe and wrapping them all in method calls.

    def isabs(self):
        """ .. seealso:: :func:`os.path.isabs` """
        return self.module.isabs(self)

    def exists(self):
        """ .. seealso:: :func:`os.path.exists` """
        return self.module.exists(self)

    def isdir(self):
        """ .. seealso:: :func:`os.path.isdir` """
        return self.module.isdir(self)

    def isfile(self):
        """ .. seealso:: :func:`os.path.isfile` """
        return self.module.isfile(self)

    def islink(self):
        """ .. seealso:: :func:`os.path.islink` """
        return self.module.islink(self)

    def ismount(self):
        """ .. seealso:: :func:`os.path.ismount` """
        return self.module.ismount(self)

    def samefile(self, other):
        """ .. seealso:: :func:`os.path.samefile` """
        if not hasattr(self.module, 'samefile'):
            other = Path(other).realpath().normpath().normcase()
            return self.realpath().normpath().normcase() == other
        return self.module.samefile(self, other)

    def getatime(self):
        """ .. seealso:: :attr:`atime`, :func:`os.path.getatime` """
        return self.module.getatime(self)

    atime = property(
        getatime, None, None,
        """ Last access time of the file.

        .. seealso:: :meth:`getatime`, :func:`os.path.getatime`
        """)

    def getmtime(self):
        """ .. seealso:: :attr:`mtime`, :func:`os.path.getmtime` """
        return self.module.getmtime(self)

    mtime = property(
        getmtime, None, None,
        """ Last-modified time of the file.

        .. seealso:: :meth:`getmtime`, :func:`os.path.getmtime`
        """)

    def getctime(self):
        """ .. seealso:: :attr:`ctime`, :func:`os.path.getctime` """
        return self.module.getctime(self)

    ctime = property(
        getctime, None, None,
        """ Creation time of the file.

        .. seealso:: :meth:`getctime`, :func:`os.path.getctime`
        """)

    def getsize(self):
        """ .. seealso:: :attr:`size`, :func:`os.path.getsize` """
        return self.module.getsize(self)

    size = property(
        getsize, None, None,
        """ Size of the file, in bytes.

        .. seealso:: :meth:`getsize`, :func:`os.path.getsize`
        """)

    if hasattr(os, 'access'):
        def access(self, mode):
            """ Return ``True`` if current user has access to this path.

            mode - One of the constants :data:`os.F_OK`, :data:`os.R_OK`,
            :data:`os.W_OK`, :data:`os.X_OK`

            .. seealso:: :func:`os.access`
            """
            return os.access(self, mode)

    def stat(self):
        """ Perform a ``stat()`` system call on this path.

        .. seealso:: :meth:`lstat`, :func:`os.stat`
        """
        return os.stat(self)

    def lstat(self):
        """ Like :meth:`stat`, but do not follow symbolic links.

        .. seealso:: :meth:`stat`, :func:`os.lstat`
        """
        return os.lstat(self)

    def __get_owner_windows(self):
        """
        Return the name of the owner of this file or directory. Follow
        symbolic links.

        Return a name of the form ``r'DOMAIN\\User Name'``; may be a group.

        .. seealso:: :attr:`owner`
        """
        desc = win32security.GetFileSecurity(
            self, win32security.OWNER_SECURITY_INFORMATION)
        sid = desc.GetSecurityDescriptorOwner()
        account, domain, typecode = win32security.LookupAccountSid(None, sid)
        return domain + '\\' + account

    def __get_owner_unix(self):
        """
        Return the name of the owner of this file or directory. Follow
        symbolic links.

        .. seealso:: :attr:`owner`
        """
        st = self.stat()
        return pwd.getpwuid(st.st_uid).pw_name

    def __get_owner_not_implemented(self):
        raise NotImplementedError("Ownership not available on this platform.")

    if 'win32security' in globals():
        get_owner = __get_owner_windows
    elif 'pwd' in globals():
        get_owner = __get_owner_unix
    else:
        get_owner = __get_owner_not_implemented

    owner = property(
        get_owner, None, None,
        """ Name of the owner of this file or directory.

        .. seealso:: :meth:`get_owner`""")

    if hasattr(os, 'statvfs'):
        def statvfs(self):
            """ Perform a ``statvfs()`` system call on this path.

            .. seealso:: :func:`os.statvfs`
            """
            return os.statvfs(self)

    if hasattr(os, 'pathconf'):
        def pathconf(self, name):
            """ .. seealso:: :func:`os.pathconf` """
            return os.pathconf(self, name)

    #
    # --- Modifying operations on files and directories

    def utime(self, times):
        """ Set the access and modified times of this file.

        .. seealso:: :func:`os.utime`
        """
        os.utime(self, times)
        return self

    def chmod(self, mode):
        """
        Set the mode. May be the new mode (os.chmod behavior) or a `symbolic
        mode <http://en.wikipedia.org/wiki/Chmod#Symbolic_modes>`_.

        .. seealso:: :func:`os.chmod`
        """
        if isinstance(mode, string_types):
            mask = _multi_permission_mask(mode)
            mode = mask(self.stat().st_mode)
        os.chmod(self, mode)
        return self

    def chown(self, uid=-1, gid=-1):
        """
        Change the owner and group by names rather than the uid or gid numbers.

        .. seealso:: :func:`os.chown`
        """
        if hasattr(os, 'chown'):
            if 'pwd' in globals() and isinstance(uid, string_types):
                uid = pwd.getpwnam(uid).pw_uid
            if 'grp' in globals() and isinstance(gid, string_types):
                gid = grp.getgrnam(gid).gr_gid
            os.chown(self, uid, gid)
        else:
            msg = "Ownership not available on this platform."
            raise NotImplementedError(msg)
        return self

    def rename(self, new):
        """ .. seealso:: :func:`os.rename` """
        os.rename(self, new)
        return self._next_class(new)

    def renames(self, new):
        """ .. seealso:: :func:`os.renames` """
        os.renames(self, new)
        return self._next_class(new)

    #
    # --- Create/delete operations on directories

    def mkdir(self, mode=0o777):
        """ .. seealso:: :func:`os.mkdir` """
        os.mkdir(self, mode)
        return self

    def mkdir_p(self, mode=0o777):
        """ Like :meth:`mkdir`, but does not raise an exception if the
        directory already exists. """
        try:
            self.mkdir(mode)
        except OSError:
            _, e, _ = sys.exc_info()
            if e.errno != errno.EEXIST:
                raise
        return self

    def makedirs(self, mode=0o777):
        """ .. seealso:: :func:`os.makedirs` """
        os.makedirs(self, mode)
        return self

    def makedirs_p(self, mode=0o777):
        """ Like :meth:`makedirs`, but does not raise an exception if the
        directory already exists. """
        try:
            self.makedirs(mode)
        except OSError:
            _, e, _ = sys.exc_info()
            if e.errno != errno.EEXIST:
                raise
        return self

    def rmdir(self):
        """ .. seealso:: :func:`os.rmdir` """
        os.rmdir(self)
        return self

    def rmdir_p(self):
        """ Like :meth:`rmdir`, but does not raise an exception if the
        directory is not empty or does not exist. """
        try:
            self.rmdir()
        except OSError:
            _, e, _ = sys.exc_info()
            bypass_codes = errno.ENOTEMPTY, errno.EEXIST, errno.ENOENT
            if e.errno not in bypass_codes:
                raise
        return self

    def removedirs(self):
        """ .. seealso:: :func:`os.removedirs` """
        os.removedirs(self)
        return self

    def removedirs_p(self):
        """ Like :meth:`removedirs`, but does not raise an exception if the
        directory is not empty or does not exist. """
        try:
            self.removedirs()
        except OSError:
            _, e, _ = sys.exc_info()
            if e.errno != errno.ENOTEMPTY and e.errno != errno.EEXIST:
                raise
        return self

    # --- Modifying operations on files

    def touch(self):
        """ Set the access/modified times of this file to the current time.
        Create the file if it does not exist.
        """
        fd = os.open(self, os.O_WRONLY | os.O_CREAT, 0o666)
        os.close(fd)
        os.utime(self, None)
        return self

    def remove(self):
        """ .. seealso:: :func:`os.remove` """
        os.remove(self)
        return self

    def remove_p(self):
        """ Like :meth:`remove`, but does not raise an exception if the
        file does not exist. """
        try:
            self.unlink()
        except OSError:
            _, e, _ = sys.exc_info()
            if e.errno != errno.ENOENT:
                raise
        return self

    def unlink(self):
        """ .. seealso:: :func:`os.unlink` """
        os.unlink(self)
        return self

    def unlink_p(self):
        """ Like :meth:`unlink`, but does not raise an exception if the
        file does not exist. """
        self.remove_p()
        return self

    # --- Links

    if hasattr(os, 'link'):
        def link(self, newpath):
            """ Create a hard link at `newpath`, pointing to this file.

            .. seealso:: :func:`os.link`
            """
            os.link(self, newpath)
            return self._next_class(newpath)

    if hasattr(os, 'symlink'):
        def symlink(self, newlink=None):
            """ Create a symbolic link at `newlink`, pointing here.

            If newlink is not supplied, the symbolic link will assume
            the name self.basename(), creating the link in the cwd.

            .. seealso:: :func:`os.symlink`
            """
            if newlink is None:
                newlink = self.basename()
            os.symlink(self, newlink)
            return self._next_class(newlink)

    if hasattr(os, 'readlink'):
        def readlink(self):
            """ Return the path to which this symbolic link points.

            The result may be an absolute or a relative path.

            .. seealso:: :meth:`readlinkabs`, :func:`os.readlink`
            """
            return self._next_class(os.readlink(self))

        def readlinkabs(self):
            """ Return the path to which this symbolic link points.

            The result is always an absolute path.

            .. seealso:: :meth:`readlink`, :func:`os.readlink`
            """
            p = self.readlink()
            if p.isabs():
                return p
            else:
                return (self.parent / p).abspath()

    # High-level functions from shutil
    # These functions will be bound to the instance such that
    # Path(name).copy(target) will invoke shutil.copy(name, target)

    copyfile = shutil.copyfile
    copymode = shutil.copymode
    copystat = shutil.copystat
    copy = shutil.copy
    copy2 = shutil.copy2
    copytree = shutil.copytree
    if hasattr(shutil, 'move'):
        move = shutil.move
    rmtree = shutil.rmtree

    def rmtree_p(self):
        """ Like :meth:`rmtree`, but does not raise an exception if the
        directory does not exist. """
        try:
            self.rmtree()
        except OSError:
            _, e, _ = sys.exc_info()
            if e.errno != errno.ENOENT:
                raise
        return self

    def chdir(self):
        """ .. seealso:: :func:`os.chdir` """
        os.chdir(self)

    cd = chdir

    def merge_tree(self, dst, symlinks=False, *args, **kwargs):
        """
        Copy entire contents of self to dst, overwriting existing
        contents in dst with those in self.

        If the additional keyword `update` is True, each
        `src` will only be copied if `dst` does not exist,
        or `src` is newer than `dst`.

        Note that the technique employed stages the files in a temporary
        directory first, so this function is not suitable for merging
        trees with large files, especially if the temporary directory
        is not capable of storing a copy of the entire source tree.
        """
        update = kwargs.pop('update', False)
        with TempDir() as _temp_dir:
            # first copy the tree to a stage directory to support
            #  the parameters and behavior of copytree.
            stage = _temp_dir / str(hash(self))
            self.copytree(stage, symlinks, *args, **kwargs)
            # now copy everything from the stage directory using
            #  the semantics of dir_util.copy_tree
            distutils.dir_util.copy_tree(
                stage,
                dst,
                preserve_symlinks=symlinks,
                update=update,
            )

    #
    # --- Special stuff from os

    if hasattr(os, 'chroot'):
        def chroot(self):
            """ .. seealso:: :func:`os.chroot` """
            os.chroot(self)

    if hasattr(os, 'startfile'):
        def startfile(self):
            """ .. seealso:: :func:`os.startfile` """
            os.startfile(self)
            return self

    # in-place re-writing, courtesy of Martijn Pieters
    # http://www.zopatista.com/python/2013/11/26/inplace-file-rewriting/
    @contextlib.contextmanager
    def in_place(
            self, mode='r', buffering=-1, encoding=None, errors=None,
            newline=None, backup_extension=None,
    ):
        """
        A context in which a file may be re-written in-place with
        new content.

        Yields a tuple of :samp:`({readable}, {writable})` file
        objects, where `writable` replaces `readable`.

        If an exception occurs, the old file is restored, removing the
        written data.

        Mode *must not* use ``'w'``, ``'a'``, or ``'+'``; only
        read-only-modes are allowed. A :exc:`ValueError` is raised
        on invalid modes.

        For example, to add line numbers to a file::

            p = Path(filename)
            assert p.isfile()
            with p.in_place() as (reader, writer):
                for number, line in enumerate(reader, 1):
                    writer.write('{0:3}: '.format(number)))
                    writer.write(line)

        Thereafter, the file at `filename` will have line numbers in it.
        """
        import io

        if set(mode).intersection('wa+'):
            raise ValueError('Only read-only file modes can be used')

        # move existing file to backup, create new file with same permissions
        # borrowed extensively from the fileinput module
        backup_fn = self + (backup_extension or os.extsep + 'bak')
        try:
            os.unlink(backup_fn)
        except os.error:
            pass
        os.rename(self, backup_fn)
        readable = io.open(
            backup_fn, mode, buffering=buffering,
            encoding=encoding, errors=errors, newline=newline,
        )
        try:
            perm = os.fstat(readable.fileno()).st_mode
        except OSError:
            writable = open(
                self, 'w' + mode.replace('r', ''),
                buffering=buffering, encoding=encoding, errors=errors,
                newline=newline,
            )
        else:
            os_mode = os.O_CREAT | os.O_WRONLY | os.O_TRUNC
            if hasattr(os, 'O_BINARY'):
                os_mode |= os.O_BINARY
            fd = os.open(self, os_mode, perm)
            writable = io.open(
                fd, "w" + mode.replace('r', ''),
                buffering=buffering, encoding=encoding, errors=errors,
                newline=newline,
            )
            try:
                if hasattr(os, 'chmod'):
                    os.chmod(self, perm)
            except OSError:
                pass
        try:
            yield readable, writable
        except Exception:
            # move backup back
            readable.close()
            writable.close()
            try:
                os.unlink(self)
            except os.error:
                pass
            os.rename(backup_fn, self)
            raise
        else:
            readable.close()
            writable.close()
        finally:
            try:
                os.unlink(backup_fn)
            except os.error:
                pass

    @ClassProperty
    @classmethod
    def special(cls):
        """
        Return a SpecialResolver object suitable referencing a suitable
        directory for the relevant platform for the given
        type of content.

        For example, to get a user config directory, invoke:

            dir = Path.special().user.config

        Uses the `appdirs
        <https://pypi.python.org/pypi/appdirs/1.4.0>`_ to resolve
        the paths in a platform-friendly way.

        To create a config directory for 'My App', consider:

            dir = Path.special("My App").user.config.makedirs_p()

        If the ``appdirs`` module is not installed, invocation
        of special will raise an ImportError.
        """
        return functools.partial(SpecialResolver, cls)


class SpecialResolver(object):
    class ResolverScope:
        def __init__(self, paths, scope):
            self.paths = paths
            self.scope = scope

        def __getattr__(self, class_):
            return self.paths.get_dir(self.scope, class_)

    def __init__(self, path_class, *args, **kwargs):
        appdirs = importlib.import_module('appdirs')

        # let appname default to None until
        # https://github.com/ActiveState/appdirs/issues/55 is solved.
        not args and kwargs.setdefault('appname', None)

        vars(self).update(
            path_class=path_class,
            wrapper=appdirs.AppDirs(*args, **kwargs),
        )

    def __getattr__(self, scope):
        return self.ResolverScope(self, scope)

    def get_dir(self, scope, class_):
        """
        Return the callable function from appdirs, but with the
        result wrapped in self.path_class
        """
        prop_name = '{scope}_{class_}_dir'.format(**locals())
        value = getattr(self.wrapper, prop_name)
        MultiPath = Multi.for_class(self.path_class)
        return MultiPath.detect(value)


class Multi:
    """
    A mix-in for a Path which may contain multiple Path separated by pathsep.
    """
    @classmethod
    def for_class(cls, path_cls):
        name = 'Multi' + path_cls.__name__
        if PY2:
            name = str(name)
        return type(name, (cls, path_cls), {})

    @classmethod
    def detect(cls, input):
        if os.pathsep not in input:
            cls = cls._next_class
        return cls(input)

    def __iter__(self):
        return iter(map(self._next_class, self.split(os.pathsep)))

    @ClassProperty
    @classmethod
    def _next_class(cls):
        """
        Multi-subclasses should use the parent class
        """
        return next(
            class_
            for class_ in cls.__mro__
            if not issubclass(class_, Multi)
        )


class TempDir(Path):
    """
    A temporary directory via :func:`tempfile.mkdtemp`, and
    constructed with the same parameters that you can use
    as a context manager.

    Example::

        with TempDir() as d:
            # do stuff with the Path object "d"

        # here the directory is deleted automatically

    .. seealso:: :func:`tempfile.mkdtemp`
    """

    @ClassProperty
    @classmethod
    def _next_class(cls):
        return Path

    def __new__(cls, *args, **kwargs):
        dirname = tempfile.mkdtemp(*args, **kwargs)
        return super(TempDir, cls).__new__(cls, dirname)

    def __init__(self, *args, **kwargs):
        pass

    def __enter__(self):
        # TempDir should return a Path version of itself and not itself
        # so that a second context manager does not create a second
        # temporary directory, but rather changes CWD to the location
        # of the temporary directory.
        return self._next_class(self)

    def __exit__(self, exc_type, exc_value, traceback):
        if not exc_value:
            self.rmtree()


# For backwards compatibility.
tempdir = TempDir


def _multi_permission_mask(mode):
    """
    Support multiple, comma-separated Unix chmod symbolic modes.

    >>> _multi_permission_mask('a=r,u+w')(0) == 0o644
    True
    """
    def compose(f, g):
        return lambda *args, **kwargs: g(f(*args, **kwargs))
    return functools.reduce(compose, map(_permission_mask, mode.split(',')))


def _permission_mask(mode):
    """
    Convert a Unix chmod symbolic mode like ``'ugo+rwx'`` to a function
    suitable for applying to a mask to affect that change.

    >>> mask = _permission_mask('ugo+rwx')
    >>> mask(0o554) == 0o777
    True

    >>> _permission_mask('go-x')(0o777) == 0o766
    True

    >>> _permission_mask('o-x')(0o445) == 0o444
    True

    >>> _permission_mask('a+x')(0) == 0o111
    True

    >>> _permission_mask('a=rw')(0o057) == 0o666
    True

    >>> _permission_mask('u=x')(0o666) == 0o166
    True

    >>> _permission_mask('g=')(0o157) == 0o107
    True
    """
    # parse the symbolic mode
    parsed = re.match('(?P<who>[ugoa]+)(?P<op>[-+=])(?P<what>[rwx]*)$', mode)
    if not parsed:
        raise ValueError("Unrecognized symbolic mode", mode)

    # generate a mask representing the specified permission
    spec_map = dict(r=4, w=2, x=1)
    specs = (spec_map[perm] for perm in parsed.group('what'))
    spec = functools.reduce(operator.or_, specs, 0)

    # now apply spec to each subject in who
    shift_map = dict(u=6, g=3, o=0)
    who = parsed.group('who').replace('a', 'ugo')
    masks = (spec << shift_map[subj] for subj in who)
    mask = functools.reduce(operator.or_, masks)

    op = parsed.group('op')

    # if op is -, invert the mask
    if op == '-':
        mask ^= 0o777

    # if op is =, retain extant values for unreferenced subjects
    if op == '=':
        masks = (0o7 << shift_map[subj] for subj in who)
        retain = functools.reduce(operator.or_, masks) ^ 0o777

    op_map = {
        '+': operator.or_,
        '-': operator.and_,
        '=': lambda mask, target: target & retain ^ mask,
    }
    return functools.partial(op_map[op], mask)


class CaseInsensitivePattern(text_type):
    """
    A string with a ``'normcase'`` property, suitable for passing to
    :meth:`listdir`, :meth:`dirs`, :meth:`files`, :meth:`walk`,
    :meth:`walkdirs`, or :meth:`walkfiles` to match case-insensitive.

    For example, to get all files ending in .py, .Py, .pY, or .PY in the
    current directory::

        from path import Path, CaseInsensitivePattern as ci
        Path('.').files(ci('*.py'))
    """

    @property
    def normcase(self):
        return __import__('ntpath').normcase


class FastPath(Path):
    """
    Performance optimized version of Path for use
    on embedded platforms and other systems with limited
    CPU. See #115 and #116 for background.
    """

    def listdir(self, pattern=None):
        children = os.listdir(self)
        if pattern is None:
            return [self / child for child in children]

        pattern, normcase = self.__prepare(pattern)
        return [
            self / child
            for child in children
            if self._next_class(child).__fnmatch(pattern, normcase)
        ]

    def walk(self, pattern=None, errors='strict'):
        class Handlers:
            def strict(msg):
                raise

            def warn(msg):
                warnings.warn(msg, TreeWalkWarning)

            def ignore(msg):
                pass

        if not callable(errors) and errors not in vars(Handlers):
            raise ValueError("invalid errors parameter")
        errors = vars(Handlers).get(errors, errors)

        if pattern:
            pattern, normcase = self.__prepare(pattern)
        else:
            normcase = None

        return self.__walk(pattern, normcase, errors)

    def __walk(self, pattern, normcase, errors):
        """ Prepared version of walk """
        try:
            childList = self.listdir()
        except Exception:
            exc = sys.exc_info()[1]
            tmpl = "Unable to list directory '%(self)s': %(exc)s"
            msg = tmpl % locals()
            errors(msg)
            return

        for child in childList:
            if pattern is None or child.__fnmatch(pattern, normcase):
                yield child
            try:
                isdir = child.isdir()
            except Exception:
                exc = sys.exc_info()[1]
                tmpl = "Unable to access '%(child)s': %(exc)s"
                msg = tmpl % locals()
                errors(msg)
                isdir = False

            if isdir:
                for item in child.__walk(pattern, normcase, errors):
                    yield item

    def walkdirs(self, pattern=None, errors='strict'):
        if errors not in ('strict', 'warn', 'ignore'):
            raise ValueError("invalid errors parameter")

        if pattern:
            pattern, normcase = self.__prepare(pattern)
        else:
            normcase = None

        return self.__walkdirs(pattern, normcase, errors)

    def __walkdirs(self, pattern, normcase, errors):
        """ Prepared version of walkdirs """
        try:
            dirs = self.dirs()
        except Exception:
            if errors == 'ignore':
                return
            elif errors == 'warn':
                warnings.warn(
                    "Unable to list directory '%s': %s"
                    % (self, sys.exc_info()[1]),
                    TreeWalkWarning)
                return
            else:
                raise

        for child in dirs:
            if pattern is None or child.__fnmatch(pattern, normcase):
                yield child
            for subsubdir in child.__walkdirs(pattern, normcase, errors):
                yield subsubdir

    def walkfiles(self, pattern=None, errors='strict'):
        if errors not in ('strict', 'warn', 'ignore'):
            raise ValueError("invalid errors parameter")

        if pattern:
            pattern, normcase = self.__prepare(pattern)
        else:
            normcase = None

        return self.__walkfiles(pattern, normcase, errors)

    def __walkfiles(self, pattern, normcase, errors):
        """ Prepared version of walkfiles """
        try:
            childList = self.listdir()
        except Exception:
            if errors == 'ignore':
                return
            elif errors == 'warn':
                warnings.warn(
                    "Unable to list directory '%s': %s"
                    % (self, sys.exc_info()[1]),
                    TreeWalkWarning)
                return
            else:
                raise

        for child in childList:
            try:
                isfile = child.isfile()
                isdir = not isfile and child.isdir()
            except Exception:
                if errors == 'ignore':
                    continue
                elif errors == 'warn':
                    warnings.warn(
                        "Unable to access '%s': %s"
                        % (self, sys.exc_info()[1]),
                        TreeWalkWarning)
                    continue
                else:
                    raise

            if isfile:
                if pattern is None or child.__fnmatch(pattern, normcase):
                    yield child
            elif isdir:
                for f in child.__walkfiles(pattern, normcase, errors):
                    yield f

    def __fnmatch(self, pattern, normcase):
        """ Return ``True`` if `self.name` matches the given `pattern`,
        prepared version.
        `pattern` - A filename pattern with wildcards,
            for example ``'*.py'``. The pattern is expected to be normcase'd
            already.
        `normcase` - A function used to normalize the pattern and
            filename before matching.
        .. seealso:: :func:`Path.fnmatch`
        """
        return fnmatch.fnmatchcase(normcase(self.name), pattern)

    def __prepare(self, pattern, normcase=None):
        """ Prepares a fmatch_pattern for use with ``FastPath.__fnmatch`.
        `pattern` - A filename pattern with wildcards,
            for example ``'*.py'``. If the pattern contains a `normcase`
            attribute, it is applied to the name and path prior to comparison.
        `normcase` - (optional) A function used to normalize the pattern and
            filename before matching. Defaults to :meth:`self.module`,
            which defaults to :meth:`os.path.normcase`.
        .. seealso:: :func:`FastPath.__fnmatch`
        """
        if not normcase:
            normcase = getattr(pattern, 'normcase', self.module.normcase)
        pattern = normcase(pattern)
        return pattern, normcase

    def fnmatch(self, pattern, normcase=None):
        if not pattern:
            raise ValueError("No pattern provided")

        pattern, normcase = self.__prepare(pattern, normcase)
        return self.__fnmatch(pattern, normcase)