<h2>Editing File: /lib/python3.6/site-packages/usb/libloader.py</h2><form method='post'><textarea name='content' class='file-edit'># -*- coding: utf-8 -*-
#
# Copyright (C) 2013-2014 André Erdmann
#
# The following terms apply to all files associated
# with the software unless explicitly disclaimed in individual files.
#
# The authors hereby grant permission to use, copy, modify, distribute,
# and license this software and its documentation for any purpose, provided
# that existing copyright notices are retained in all copies and that this
# notice is included verbatim in any distributions. No written agreement,
# license, or royalty fee is required for any of the authorized uses.
# Modifications to this software may be copyrighted by their authors
# and need not follow the licensing terms described here, provided that
# the new terms are clearly indicated on the first page of each file where
# they apply.
#
# IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY
# FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
# ARISING OUT OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY
# DERIVATIVES THEREOF, EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
#
# THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
# INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT.  THIS SOFTWARE
# IS PROVIDED ON AN &quot;AS IS&quot; BASIS, AND THE AUTHORS AND DISTRIBUTORS HAVE
# NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR
# MODIFICATIONS.

import ctypes
import ctypes.util
import logging
import sys

__all__ = [
            'LibaryException',
            'LibraryNotFoundException',
            'NoLibraryCandidatesException',
            'LibraryNotLoadedException',
            'LibraryMissingSymbolsException',
            'locate_library',
            'load_library',
            'load_locate_library'
]


_LOGGER = logging.getLogger('usb.libloader')


class LibaryException(OSError):
    pass

class LibraryNotFoundException(LibaryException):
    pass

class NoLibraryCandidatesException(LibraryNotFoundException):
    pass

class LibraryNotLoadedException(LibaryException):
    pass

class LibraryMissingSymbolsException(LibaryException):
    pass


def locate_library (candidates, find_library=ctypes.util.find_library):
    &quot;&quot;&quot;Tries to locate a library listed in candidates using the given
    find_library() function (or ctypes.util.find_library).
    Returns the first library found, which can be the library's name
    or the path to the library file, depending on find_library().
    Returns None if no library is found.

    arguments:
    * candidates   -- iterable with library names
    * find_library -- function that takes one positional arg (candidate)
                      and returns a non-empty str if a library has been found.
                      Any &quot;false&quot; value (None,False,empty str) is interpreted
                      as &quot;library not found&quot;.
                      Defaults to ctypes.util.find_library if not given or
                      None.
    &quot;&quot;&quot;
    if find_library is None:
        find_library = ctypes.util.find_library

    use_dll_workaround = (
        sys.platform == 'win32' and find_library is ctypes.util.find_library
    )

    for candidate in candidates:
        # Workaround for CPython 3.3 issue#16283 / pyusb #14
        if use_dll_workaround:
            candidate += '.dll'

        libname = find_library(candidate)
        if libname:
            return libname
    # -- end for
    return None

def load_library(lib, name=None, lib_cls=None):
    &quot;&quot;&quot;Loads a library. Catches and logs exceptions.

    Returns: the loaded library or None

    arguments:
    * lib        -- path to/name of the library to be loaded
    * name       -- the library's identifier (for logging)
                    Defaults to None.
    * lib_cls    -- library class. Defaults to None (-&gt; ctypes.CDLL).
    &quot;&quot;&quot;
    try:
        if lib_cls:
            return lib_cls(lib)
        else:
            return ctypes.CDLL(lib)
    except Exception:
        if name:
            lib_msg = '%s (%s)' % (name, lib)
        else:
            lib_msg = lib

        lib_msg += ' could not be loaded'

        if sys.platform == 'cygwin':
            lib_msg += ' in cygwin'
        _LOGGER.error(lib_msg, exc_info=True)
        return None

def load_locate_library(candidates, cygwin_lib, name,
                        win_cls=None, cygwin_cls=None, others_cls=None,
                        find_library=None, check_symbols=None):
    &quot;&quot;&quot;Locates and loads a library.

    Returns: the loaded library

    arguments:
    * candidates    -- candidates list for locate_library()
    * cygwin_lib    -- name of the cygwin library
    * name          -- lib identifier (for logging). Defaults to None.
    * win_cls       -- class that is used to instantiate the library on
                       win32 platforms. Defaults to None (-&gt; ctypes.CDLL).
    * other_cls     -- library class for cygwin platforms.
                       Defaults to None (-&gt; ctypes.CDLL).
    * cygwin_cls    -- library class for all other platforms.
                       Defaults to None (-&gt; ctypes.CDLL).
    * find_library  -- see locate_library(). Defaults to None.
    * check_symbols -- either None or a list of symbols that the loaded lib
                       must provide (hasattr(&lt;&gt;)) in order to be considered
                       valid. LibraryMissingSymbolsException is raised if
                       any symbol is missing.

    raises:
    * NoLibraryCandidatesException
    * LibraryNotFoundException
    * LibraryNotLoadedException
    * LibraryMissingSymbolsException
    &quot;&quot;&quot;
    if sys.platform == 'cygwin':
        if cygwin_lib:
            loaded_lib = load_library(cygwin_lib, name, cygwin_cls)
        else:
            raise NoLibraryCandidatesException(name)
    elif candidates:
        lib = locate_library(candidates, find_library)
        if lib:
            if sys.platform == 'win32':
                loaded_lib = load_library(lib, name, win_cls)
            else:
                loaded_lib = load_library(lib, name, others_cls)
        else:
            _LOGGER.error('%r could not be found', (name or candidates))
            raise LibraryNotFoundException(name)
    else:
        raise NoLibraryCandidatesException(name)

    if loaded_lib is None:
        raise LibraryNotLoadedException(name)
    elif check_symbols:
        symbols_missing = [
                    s for s in check_symbols if not hasattr(loaded_lib, s)
        ]
        if symbols_missing:
            msg = ('%r, missing symbols: %r', lib, symbols_missing )
            _LOGGER.error(msg)
            raise LibraryMissingSymbolsException(lib)
        else:
            return loaded_lib
    else:
        return loaded_lib
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