IPython/utils/py3compat.py

# coding: utf-8
"""Compatibility tricks for Python 3. Mainly to do with unicode."""
import functools
import os
import sys
import re
import shutil
import types

from .encoding import DEFAULT_ENCODING

def no_code(x, encoding=None):
    return x

def decode(s, encoding=None):
    encoding = encoding or DEFAULT_ENCODING
    return s.decode(encoding, "replace")

def encode(u, encoding=None):
    encoding = encoding or DEFAULT_ENCODING
    return u.encode(encoding, "replace")


def cast_unicode(s, encoding=None):
    if isinstance(s, bytes):
        return decode(s, encoding)
    return s

def cast_bytes(s, encoding=None):
    if not isinstance(s, bytes):
        return encode(s, encoding)
    return s

def buffer_to_bytes(buf):
    """Cast a buffer object to bytes"""
    if not isinstance(buf, bytes):
        buf = bytes(buf)
    return buf

def _modify_str_or_docstring(str_change_func):
    @functools.wraps(str_change_func)
    def wrapper(func_or_str):
        if isinstance(func_or_str, string_types):
            func = None
            doc = func_or_str
        else:
            func = func_or_str
            doc = func.__doc__
        
        doc = str_change_func(doc)
        
        if func:
            func.__doc__ = doc
            return func
        return doc
    return wrapper

def safe_unicode(e):
    """unicode(e) with various fallbacks. Used for exceptions, which may not be
    safe to call unicode() on.
    """
    try:
        return unicode_type(e)
    except UnicodeError:
        pass

    try:
        return str_to_unicode(str(e))
    except UnicodeError:
        pass

    try:
        return str_to_unicode(repr(e))
    except UnicodeError:
        pass

    return u'Unrecoverably corrupt evalue'

# shutil.which from Python 3.4
def _shutil_which(cmd, mode=os.F_OK | os.X_OK, path=None):
    """Given a command, mode, and a PATH string, return the path which
    conforms to the given mode on the PATH, or None if there is no such
    file.

    `mode` defaults to os.F_OK | os.X_OK. `path` defaults to the result
    of os.environ.get("PATH"), or can be overridden with a custom search
    path.
    
    This is a backport of shutil.which from Python 3.4
    """
    # Check that a given file can be accessed with the correct mode.
    # Additionally check that `file` is not a directory, as on Windows
    # directories pass the os.access check.
    def _access_check(fn, mode):
        return (os.path.exists(fn) and os.access(fn, mode)
                and not os.path.isdir(fn))

    # If we're given a path with a directory part, look it up directly rather
    # than referring to PATH directories. This includes checking relative to the
    # current directory, e.g. ./script
    if os.path.dirname(cmd):
        if _access_check(cmd, mode):
            return cmd
        return None

    if path is None:
        path = os.environ.get("PATH", os.defpath)
    if not path:
        return None
    path = path.split(os.pathsep)

    if sys.platform == "win32":
        # The current directory takes precedence on Windows.
        if not os.curdir in path:
            path.insert(0, os.curdir)

        # PATHEXT is necessary to check on Windows.
        pathext = os.environ.get("PATHEXT", "").split(os.pathsep)
        # See if the given file matches any of the expected path extensions.
        # This will allow us to short circuit when given "python.exe".
        # If it does match, only test that one, otherwise we have to try
        # others.
        if any(cmd.lower().endswith(ext.lower()) for ext in pathext):
            files = [cmd]
        else:
            files = [cmd + ext for ext in pathext]
    else:
        # On other platforms you don't have things like PATHEXT to tell you
        # what file suffixes are executable, so just pass on cmd as-is.
        files = [cmd]

    seen = set()
    for dir in path:
        normdir = os.path.normcase(dir)
        if not normdir in seen:
            seen.add(normdir)
            for thefile in files:
                name = os.path.join(dir, thefile)
                if _access_check(name, mode):
                    return name
    return None

if sys.version_info[0] >= 3:
    PY3 = True
    
    # keep reference to builtin_mod because the kernel overrides that value
    # to forward requests to a frontend.
    def input(prompt=''):
        return builtin_mod.input(prompt)
    
    builtin_mod_name = "builtins"
    import builtins as builtin_mod
    
    str_to_unicode = no_code
    unicode_to_str = no_code
    str_to_bytes = encode
    bytes_to_str = decode
    cast_bytes_py2 = no_code
    cast_unicode_py2 = no_code
    buffer_to_bytes_py2 = no_code
    
    string_types = (str,)
    unicode_type = str
    
    which = shutil.which
    
    def isidentifier(s, dotted=False):
        if dotted:
            return all(isidentifier(a) for a in s.split("."))
        return s.isidentifier()

    xrange = range
    def iteritems(d): return iter(d.items())
    def itervalues(d): return iter(d.values())
    getcwd = os.getcwd
    
    MethodType = types.MethodType

    def execfile(fname, glob, loc=None, compiler=None):
        loc = loc if (loc is not None) else glob
        with open(fname, 'rb') as f:
            compiler = compiler or compile
            exec(compiler(f.read(), fname, 'exec'), glob, loc)
    
    # Refactor print statements in doctests.
    _print_statement_re = re.compile(r"\bprint (?P<expr>.*)$", re.MULTILINE)
    def _print_statement_sub(match):
        expr = match.groups('expr')
        return "print(%s)" % expr
    
    @_modify_str_or_docstring
    def doctest_refactor_print(doc):
        """Refactor 'print x' statements in a doctest to print(x) style. 2to3
        unfortunately doesn't pick up on our doctests.
        
        Can accept a string or a function, so it can be used as a decorator."""
        return _print_statement_re.sub(_print_statement_sub, doc)
    
    # Abstract u'abc' syntax:
    @_modify_str_or_docstring
    def u_format(s):
        """"{u}'abc'" --> "'abc'" (Python 3)
        
        Accepts a string or a function, so it can be used as a decorator."""
        return s.format(u='')
    
    def get_closure(f):
        """Get a function's closure attribute"""
        return f.__closure__

else:
    PY3 = False
    
    # keep reference to builtin_mod because the kernel overrides that value
    # to forward requests to a frontend.
    def input(prompt=''):
        return builtin_mod.raw_input(prompt)
    
    builtin_mod_name = "__builtin__"
    import __builtin__ as builtin_mod
    
    str_to_unicode = decode
    unicode_to_str = encode
    str_to_bytes = no_code
    bytes_to_str = no_code
    cast_bytes_py2 = cast_bytes
    cast_unicode_py2 = cast_unicode
    buffer_to_bytes_py2 = buffer_to_bytes
    
    string_types = (str, unicode)
    unicode_type = unicode
    
    import re
    _name_re = re.compile(r"[a-zA-Z_][a-zA-Z0-9_]*$")
    def isidentifier(s, dotted=False):
        if dotted:
            return all(isidentifier(a) for a in s.split("."))
        return bool(_name_re.match(s))
    
    xrange = xrange
    def iteritems(d): return d.iteritems()
    def itervalues(d): return d.itervalues()
    getcwd = os.getcwdu

    def MethodType(func, instance):
        return types.MethodType(func, instance, type(instance))
    
    def doctest_refactor_print(func_or_str):
        return func_or_str

    def get_closure(f):
        """Get a function's closure attribute"""
        return f.func_closure
    
    which = _shutil_which

    # Abstract u'abc' syntax:
    @_modify_str_or_docstring
    def u_format(s):
        """"{u}'abc'" --> "u'abc'" (Python 2)
        
        Accepts a string or a function, so it can be used as a decorator."""
        return s.format(u='u')

    if sys.platform == 'win32':
        def execfile(fname, glob=None, loc=None, compiler=None):
            loc = loc if (loc is not None) else glob
            scripttext = builtin_mod.open(fname).read()+ '\n'
            # compile converts unicode filename to str assuming
            # ascii. Let's do the conversion before calling compile
            if isinstance(fname, unicode):
                filename = unicode_to_str(fname)
            else:
                filename = fname
            compiler = compiler or compile
            exec(compiler(scripttext, filename, 'exec'), glob, loc)

    else:
        def execfile(fname, glob=None, loc=None, compiler=None):
            if isinstance(fname, unicode):
                filename = fname.encode(sys.getfilesystemencoding())
            else:
                filename = fname
            where = [ns for ns in [glob, loc] if ns is not None]
            if compiler is None:
                builtin_mod.execfile(filename, *where)
            else:
                scripttext = builtin_mod.open(fname).read().rstrip() + '\n'
                exec(compiler(scripttext, filename, 'exec'), glob, loc)


PY2 = not PY3


def annotate(**kwargs):
    """Python 3 compatible function annotation for Python 2."""
    if not kwargs:
        raise ValueError('annotations must be provided as keyword arguments')
    def dec(f):
        if hasattr(f, '__annotations__'):
            for k, v in kwargs.items():
                f.__annotations__[k] = v
        else:
            f.__annotations__ = kwargs
        return f
    return dec


# Parts below taken from six:
# Copyright (c) 2010-2013 Benjamin Peterson
#
# 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.

def with_metaclass(meta, *bases):
    """Create a base class with a metaclass."""
    return meta("_NewBase", bases, {})