path.py

# encoding: utf-8
"""
Utilities for path handling.
"""

# Copyright (c) IPython Development Team.
# Distributed under the terms of the Modified BSD License.

import os
import sys
import errno
import shutil
import random

from . import py3compat


fs_encoding = sys.getfilesystemencoding()


def filefind(filename, path_dirs=None):
    """Find a file by looking through a sequence of paths.

    This iterates through a sequence of paths looking for a file and returns
    the full, absolute path of the first occurence of the file.  If no set of
    path dirs is given, the filename is tested as is, after running through
    :func:`expandvars` and :func:`expanduser`.  Thus a simple call::

        filefind('myfile.txt')

    will find the file in the current working dir, but::

        filefind('~/myfile.txt')

    Will find the file in the users home directory.  This function does not
    automatically try any paths, such as the cwd or the user's home directory.

    Parameters
    ----------
    filename : str
        The filename to look for.
    path_dirs : str, None or sequence of str
        The sequence of paths to look for the file in.  If None, the filename
        need to be absolute or be in the cwd.  If a string, the string is
        put into a sequence and the searched.  If a sequence, walk through
        each element and join with ``filename``, calling :func:`expandvars`
        and :func:`expanduser` before testing for existence.

    Returns
    -------
    Raises :exc:`IOError` or returns absolute path to file.
    """

    # If paths are quoted, abspath gets confused, strip them...
    filename = filename.strip('"').strip("'")
    # If the input is an absolute path, just check it exists
    if os.path.isabs(filename) and os.path.isfile(filename):
        return filename

    if path_dirs is None:
        path_dirs = ("",)
    elif isinstance(path_dirs, py3compat.string_types):
        path_dirs = (path_dirs,)

    for path in path_dirs:
        if path == '.': path = py3compat.getcwd()
        testname = expand_path(os.path.join(path, filename))
        if os.path.isfile(testname):
            return os.path.abspath(testname)

    raise IOError("File %r does not exist in any of the search paths: %r" %
                  (filename, path_dirs) )


def expand_path(s):
    """Expand $VARS and ~names in a string, like a shell

    :Examples:

       In [2]: os.environ['FOO']='test'

       In [3]: expand_path('variable FOO is $FOO')
       Out[3]: 'variable FOO is test'
    """
    # This is a pretty subtle hack. When expand user is given a UNC path
    # on Windows (\\server\share$\%username%), os.path.expandvars, removes
    # the $ to get (\\server\share\%username%). I think it considered $
    # alone an empty var. But, we need the $ to remains there (it indicates
    # a hidden share).
    if os.name=='nt':
        s = s.replace('$\\', 'IPYTHON_TEMP')
    s = os.path.expandvars(os.path.expanduser(s))
    if os.name=='nt':
        s = s.replace('IPYTHON_TEMP', '$\\')
    return s


try:
    ENOLINK = errno.ENOLINK
except AttributeError:
    ENOLINK = 1998

def link(src, dst):
    """Hard links ``src`` to ``dst``, returning 0 or errno.

    Note that the special errno ``ENOLINK`` will be returned if ``os.link`` isn't
    supported by the operating system.
    """

    if not hasattr(os, "link"):
        return ENOLINK
    link_errno = 0
    try:
        os.link(src, dst)
    except OSError as e:
        link_errno = e.errno
    return link_errno


def link_or_copy(src, dst):
    """Attempts to hardlink ``src`` to ``dst``, copying if the link fails.

    Attempts to maintain the semantics of ``shutil.copy``.

    Because ``os.link`` does not overwrite files, a unique temporary file
    will be used if the target already exists, then that file will be moved
    into place.
    """

    if os.path.isdir(dst):
        dst = os.path.join(dst, os.path.basename(src))

    link_errno = link(src, dst)
    if link_errno == errno.EEXIST:
        if os.stat(src).st_ino == os.stat(dst).st_ino:
            # dst is already a hard link to the correct file, so we don't need
            # to do anything else. If we try to link and rename the file
            # anyway, we get duplicate files - see http://bugs.python.org/issue21876
            return

        new_dst = dst + "-temp-%04X" %(random.randint(1, 16**4), )
        try:
            link_or_copy(src, new_dst)
        except:
            try:
                os.remove(new_dst)
            except OSError:
                pass
            raise
        os.rename(new_dst, dst)
    elif link_errno != 0:
        # Either link isn't supported, or the filesystem doesn't support
        # linking, or 'src' and 'dst' are on different filesystems.
        shutil.copy(src, dst)


def ensure_dir_exists(path, mode=0o755):
    """ensure that a directory exists
    
    If it doesn't exist, try to create it and protect against a race condition
    if another process is doing the same.
    
    The default permissions are 755, which differ from os.makedirs default of 777.
    """
    if not os.path.exists(path):
        try:
            os.makedirs(path, mode=mode)
        except OSError as e:
            if e.errno != errno.EEXIST:
                raise
    elif not os.path.isdir(path):
        raise IOError("%r exists but is not a directory" % path)