future.utils — Python-Future documentation

# Source code for future.utils

    """
    A selection of cross-compatible functions for Python 2 and 3.

    This module exports useful functions for 2/3 compatible code:

        * bind_method: binds functions to classes
        * ``native_str_to_bytes`` and ``bytes_to_native_str``
        * ``native_str``: always equal to the native platform string object (because
          this may be shadowed by imports from future.builtins)
        * lists: lrange(), lmap(), lzip(), lfilter()
        * iterable method compatibility:
            - iteritems, iterkeys, itervalues
            - viewitems, viewkeys, viewvalues

            These use the original method if available, otherwise they use items,
            keys, values.

        * types:

            * text_type: unicode in Python 2, str in Python 3
            * string_types: basestring in Python 2, str in Python 3
            * binary_type: str in Python 2, bytes in Python 3
            * integer_types: (int, long) in Python 2, int in Python 3
            * class_types: (type, types.ClassType) in Python 2, type in Python 3

        * bchr(c):
            Take an integer and make a 1-character byte string
        * bord(c)
            Take the result of indexing on a byte string and make an integer
        * tobytes(s)
            Take a text string, a byte string, or a sequence of characters taken
            from a byte string, and make a byte string.

        * raise_from()
        * raise_with_traceback()

    This module also defines these decorators:

        * ``python_2_unicode_compatible``
        * ``with_metaclass``
        * ``implements_iterator``

    Some of the functions in this module come from the following sources:

        * Jinja2 (BSD licensed: see
          https://github.com/mitsuhiko/jinja2/blob/master/LICENSE)
        * Pandas compatibility module pandas.compat
        * six.py by Benjamin Peterson
        * Django
    """

    import types
    import sys
    import numbers
    import functools
    import copy
    import inspect

    PY3 = sys.version_info[0] >= 3
    PY34_PLUS = sys.version_info[0:2] >= (3, 4)
    PY35_PLUS = sys.version_info[0:2] >= (3, 5)
    PY36_PLUS = sys.version_info[0:2] >= (3, 6)
    PY37_PLUS = sys.version_info[0:2] >= (3, 7)
    PY38_PLUS = sys.version_info[0:2] >= (3, 8)
    PY39_PLUS = sys.version_info[0:2] >= (3, 9)
    PY2 = sys.version_info[0] == 2
    PY26 = sys.version_info[0:2] == (2, 6)
    PY27 = sys.version_info[0:2] == (2, 7)
    PYPY = hasattr(sys, 'pypy_translation_info')

    def python_2_unicode_compatible(cls):
        """
        A decorator that defines __unicode__ and __str__ methods under Python
        2. Under Python 3, this decorator is a no-op.

        To support Python 2 and 3 with a single code base, define a __str__
        method returning unicode text and apply this decorator to the class, like
        this::

        >>> from future.utils import python_2_unicode_compatible

        >>> @python_2_unicode_compatible
        ... class MyClass(object):
        ...     def __str__(self):
        ...         return u'Unicode string: \u5b54\u5b50'

        >>> a = MyClass()

        Then, after this import:

        >>> from future.builtins import str

        the following is ``True`` on both Python 3 and 2::

        >>> str(a) == a.encode('utf-8').decode('utf-8')
        True

        and, on a Unicode-enabled terminal with the right fonts, these both print the
        Chinese characters for Confucius::

        >>> print(a)
        >>> print(str(a))

        The implementation comes from django.utils.encoding.
        """
        if not PY3:
            cls.__unicode__ = cls.__str__
            cls.__str__ = lambda self: self.__unicode__().encode('utf-8')
        return cls

    def with_metaclass(meta, *bases):
        """
        Function from jinja2/_compat.py. License: BSD.

        Use it like this::

            class BaseForm(object):
                pass

            class FormType(type):
                pass

            class Form(with_metaclass(FormType, BaseForm)):
                pass

        This requires a bit of explanation: the basic idea is to make a
        dummy metaclass for one level of class instantiation that replaces
        itself with the actual metaclass.  Because of internal type checks
        we also need to make sure that we downgrade the custom metaclass
        for one level to something closer to type (that's why __call__ and
        __init__ comes back from type etc.).

        This has the advantage over six.with_metaclass of not introducing
        dummy classes into the final MRO.
        """
        class metaclass(meta):
            __call__ = type.__call__
            __init__ = type.__init__
            def __new__(cls, name, this_bases, d):
                if this_bases is None:
                    return type.__new__(cls, name, (), d)
                return meta(name, bases, d)
        return metaclass('temporary_class', None, {})

    # Definitions from pandas.compat and six.py follow:
    if PY3:
        def bchr(s):
            return bytes([s])
        def bstr(s):
            if isinstance(s, str):
                return bytes(s, 'latin-1')
            else:
                return bytes(s)
        def bord(s):
            return s

        string_types = str,
        integer_types = int,
        class_types = type,
        text_type = str
        binary_type = bytes

    else:
        # Python 2
        def bchr(s):
            return chr(s)
        def bstr(s):
            return str(s)
        def bord(s):
            return ord(s)

        string_types = basestring,
        integer_types = (int, long)
        class_types = (type, types.ClassType)
        text_type = unicode
        binary_type = str

    ###

    if PY3:
        def tobytes(s):
            if isinstance(s, bytes):
                return s
            else:
                if isinstance(s, str):
                    return s.encode('latin-1')
                else:
                    return bytes(s)
    else:
        # Python 2

        def tobytes(s):
            if isinstance(s, unicode):
                return s.encode('latin-1')
            else:
                return ''.join(s)

    tobytes.__doc__ = """
        Encodes to latin-1 (where the first 256 chars are the same as
        ASCII.)
        """

    if PY3:
        def native_str_to_bytes(s, encoding='utf-8'):
            return s.encode(encoding)

        def bytes_to_native_str(b, encoding='utf-8'):
            return b.decode(encoding)

        def text_to_native_str(t, encoding=None):
            return t
    else:
        # Python 2

        def native_str_to_bytes(s, encoding=None):
            from future.types import newbytes    # to avoid a circular import
            return newbytes(s)

        def bytes_to_native_str(b, encoding=None):
            return native(b)

        def text_to_native_str(t, encoding='ascii'):
            """
            Use this to create a Py2 native string when "from __future__ import
            unicode_literals" is in effect.
            """
            return unicode(t).encode(encoding)

    native_str_to_bytes.__doc__ = """
        On Py3, returns an encoded string.
        On Py2, returns a newbytes type, ignoring the ``encoding`` argument.
        """

    if PY3:
        # list-producing versions of the major Python iterating functions
        def lrange(*args, **kwargs):
            return list(range(*args, **kwargs))

        def lzip(*args, **kwargs):
            return list(zip(*args, **kwargs))

        def lmap(*args, **kwargs):
            return list(map(*args, **kwargs))

        def lfilter(*args, **kwargs):
            return list(filter(*args, **kwargs))
    else:
        import __builtin__
        # Python 2-builtin ranges produce lists
        lrange = __builtin__.range
        lzip = __builtin__.zip
        lmap = __builtin__.map
        lfilter = __builtin__.filter

    def isidentifier(s, dotted=False):
        '''
        A function equivalent to the str.isidentifier method on Py3
        '''
        if dotted:
            return all(isidentifier(a) for a in s.split('.'))
        if PY3:
            return s.isidentifier()
        else:
            import re
            _name_re = re.compile(r"[a-zA-Z_][a-zA-Z0-9_]*$")
            return bool(_name_re.match(s))

    def viewitems(obj, **kwargs):
        """
        Function for iterating over dictionary items with the same set-like
        behaviour on Py2.7 as on Py3.

        Passes kwargs to method."""
        func = getattr(obj, "viewitems", None)
        if not func:
            func = obj.items
        return func(**kwargs)

    def viewkeys(obj, **kwargs):
        """
        Function for iterating over dictionary keys with the same set-like
        behaviour on Py2.7 as on Py3.

        Passes kwargs to method."""
        func = getattr(obj, "viewkeys", None)
        if not func:
            func = obj.keys
        return func(**kwargs)

    def viewvalues(obj, **kwargs):
        """
        Function for iterating over dictionary values with the same set-like
        behaviour on Py2.7 as on Py3.

        Passes kwargs to method."""
        func = getattr(obj, "viewvalues", None)
        if not func:
            func = obj.values
        return func(**kwargs)

    def iteritems(obj, **kwargs):
        """Use this only if compatibility with Python versions before 2.7 is
        required. Otherwise, prefer viewitems().
        """
        func = getattr(obj, "iteritems", None)
        if not func:
            func = obj.items
        return func(**kwargs)

    def iterkeys(obj, **kwargs):
        """Use this only if compatibility with Python versions before 2.7 is
        required. Otherwise, prefer viewkeys().
        """
        func = getattr(obj, "iterkeys", None)
        if not func:
            func = obj.keys
        return func(**kwargs)

    def itervalues(obj, **kwargs):
        """Use this only if compatibility with Python versions before 2.7 is
        required. Otherwise, prefer viewvalues().
        """
        func = getattr(obj, "itervalues", None)
        if not func:
            func = obj.values
        return func(**kwargs)

    def bind_method(cls, name, func):
        """Bind a method to class, python 2 and python 3 compatible.

        Parameters
        ----------

        cls : type
            class to receive bound method
        name : basestring
            name of method on class instance
        func : function
            function to be bound as method

        Returns
        -------
        None
        """
        # only python 2 has an issue with bound/unbound methods
        if not PY3:
            setattr(cls, name, types.MethodType(func, None, cls))
        else:
            setattr(cls, name, func)

    def getexception():
        return sys.exc_info()[1]

    def _get_caller_globals_and_locals():
        """
        Returns the globals and locals of the calling frame.

        Is there an alternative to frame hacking here?
        """
        caller_frame = inspect.stack()[2]
        myglobals = caller_frame[0].f_globals
        mylocals = caller_frame[0].f_locals
        return myglobals, mylocals

    def _repr_strip(mystring):
        """
        Returns the string without any initial or final quotes.
        """
        r = repr(mystring)
        if r.startswith("'") and r.endswith("'"):
            return r[1:-1]
        else:
            return r

    if PY3:
        def raise_from(exc, cause):
            """
            Equivalent to:

                raise EXCEPTION from CAUSE

            on Python 3. (See PEP 3134).
            """
            myglobals, mylocals = _get_caller_globals_and_locals()

            # We pass the exception and cause along with other globals
            # when we exec():
            myglobals = myglobals.copy()
            myglobals['__python_future_raise_from_exc'] = exc
            myglobals['__python_future_raise_from_cause'] = cause
            execstr = "raise __python_future_raise_from_exc from __python_future_raise_from_cause"
            exec(execstr, myglobals, mylocals)

        def raise_(tp, value=None, tb=None):
            """
            A function that matches the Python 2.x ``raise`` statement. This
            allows re-raising exceptions with the cls value and traceback on
            Python 2 and 3.
            """
            if isinstance(tp, BaseException):
                # If the first object is an instance, the type of the exception
                # is the class of the instance, the instance itself is the value,
                # and the second object must be None.
                if value is not None:
                    raise TypeError("instance exception may not have a separate value")
                exc = tp
            elif isinstance(tp, type) and not issubclass(tp, BaseException):
                # If the first object is a class, it becomes the type of the
                # exception.
                raise TypeError("class must derive from BaseException, not %s" % tp.__name__)
            else:
                # The second object is used to determine the exception value: If it
                # is an instance of the class, the instance becomes the exception
                # value. If the second object is a tuple, it is used as the argument
                # list for the class constructor; if it is None, an empty argument
                # list is used, and any other object is treated as a single argument
                # to the constructor. The instance so created by calling the
                # constructor is used as the exception value.
                if isinstance(value, tp):
                    exc = value
                elif isinstance(value, tuple):
                    exc = tp(*value)
                elif value is None:
                    exc = tp()
                else:
                    exc = tp(value)

            if exc.__traceback__ is not tb:
                raise exc.with_traceback(tb)
            raise exc

        def raise_with_traceback(exc, traceback=Ellipsis):
            if traceback == Ellipsis:
                _, _, traceback = sys.exc_info()
            raise exc.with_traceback(traceback)

    else:
        def raise_from(exc, cause):
            """
            Equivalent to:

                raise EXCEPTION from CAUSE

            on Python 3. (See PEP 3134).
            """
            # Is either arg an exception class (e.g. IndexError) rather than
            # instance (e.g. IndexError('my message here')? If so, pass the
            # name of the class undisturbed through to "raise ... from ...".
            if isinstance(exc, type) and issubclass(exc, Exception):
                e = exc()
                # exc = exc.__name__
                # execstr = "e = " + _repr_strip(exc) + "()"
                # myglobals, mylocals = _get_caller_globals_and_locals()
                # exec(execstr, myglobals, mylocals)
            else:
                e = exc
            e.__suppress_context__ = False
            if isinstance(cause, type) and issubclass(cause, Exception):
                e.__cause__ = cause()
                e.__cause__.__traceback__ = sys.exc_info()[2]
                e.__suppress_context__ = True
            elif cause is None:
                e.__cause__ = None
                e.__suppress_context__ = True
            elif isinstance(cause, BaseException):
                e.__cause__ = cause
                object.__setattr__(e.__cause__,  '__traceback__', sys.exc_info()[2])
                e.__suppress_context__ = True
            else:
                raise TypeError("exception causes must derive from BaseException")
            e.__context__ = sys.exc_info()[1]
            raise e

        exec('''
    def raise_(tp, value=None, tb=None):
        raise tp, value, tb

    def raise_with_traceback(exc, traceback=Ellipsis):
        if traceback == Ellipsis:
            _, _, traceback = sys.exc_info()
        raise exc, None, traceback
    '''.strip())

    raise_with_traceback.__doc__ = (
    """Raise exception with existing traceback.
    If traceback is not passed, uses sys.exc_info() to get traceback."""
    )

    # Deprecated alias for backward compatibility with ``future`` versions < 0.11:
    reraise = raise_

    def implements_iterator(cls):
        '''
        From jinja2/_compat.py. License: BSD.

        Use as a decorator like this::

            @implements_iterator
            class UppercasingIterator(object):
                def __init__(self, iterable):
                    self._iter = iter(iterable)
                def __iter__(self):
                    return self
                def __next__(self):
                    return next(self._iter).upper()

        '''
        if PY3:
            return cls
        else:
            cls.next = cls.__next__
            del cls.__next__
            return cls

    if PY3:
        get_next = lambda x: x.__next__
    else:
        get_next = lambda x: x.next

    def encode_filename(filename):
        if PY3:
            return filename
        else:
            if isinstance(filename, unicode):
                return filename.encode('utf-8')
            return filename

    def is_new_style(cls):
        """
        Python 2.7 has both new-style and old-style classes. Old-style classes can
        be pesky in some circumstances, such as when using inheritance.  Use this
        function to test for whether a class is new-style. (Python 3 only has
        new-style classes.)
        """
        return hasattr(cls, '__class__') and ('__dict__' in dir(cls)
                                              or hasattr(cls, '__slots__'))

    # The native platform string and bytes types. Useful because ``str`` and
    # ``bytes`` are redefined on Py2 by ``from future.builtins import *``.
    native_str = str
    native_bytes = bytes

    def istext(obj):
        """
        Deprecated. Use::
            >>> isinstance(obj, str)
        after this import:
            >>> from future.builtins import str
        """
        return isinstance(obj, type(u''))

    def isbytes(obj):
        """
        Deprecated. Use::
            >>> isinstance(obj, bytes)
        after this import:
            >>> from future.builtins import bytes
        """
        return isinstance(obj, type(b''))

    def isnewbytes(obj):
        """
        Equivalent to the result of ``type(obj)  == type(newbytes)``
        in other words, it is REALLY a newbytes instance, not a Py2 native str
        object?

        Note that this does not cover subclasses of newbytes, and it is not
        equivalent to ininstance(obj, newbytes)
        """
        return type(obj).__name__ == 'newbytes'

    def isint(obj):
        """
        Deprecated. Tests whether an object is a Py3 ``int`` or either a Py2 ``int`` or
        ``long``.

        Instead of using this function, you can use:

            >>> from future.builtins import int
            >>> isinstance(obj, int)

        The following idiom is equivalent:

            >>> from numbers import Integral
            >>> isinstance(obj, Integral)
        """

        return isinstance(obj, numbers.Integral)

    def native(obj):
        """
        On Py3, this is a no-op: native(obj) -> obj

        On Py2, returns the corresponding native Py2 types that are
        superclasses for backported objects from Py3:

        >>> from builtins import str, bytes, int

        >>> native(str(u'ABC'))
        u'ABC'
        >>> type(native(str(u'ABC')))
        unicode

        >>> native(bytes(b'ABC'))
        b'ABC'
        >>> type(native(bytes(b'ABC')))
        bytes

        >>> native(int(10**20))
        100000000000000000000L
        >>> type(native(int(10**20)))
        long

        Existing native types on Py2 will be returned unchanged:

        >>> type(native(u'ABC'))
        unicode
        """
        if hasattr(obj, '__native__'):
            return obj.__native__()
        else:
            return obj

    # Implementation of exec_ is from ``six``:
    if PY3:
        import builtins
        exec_ = getattr(builtins, "exec")
    else:
        def exec_(code, globs=None, locs=None):
            """Execute code in a namespace."""
            if globs is None:
                frame = sys._getframe(1)
                globs = frame.f_globals
                if locs is None:
                    locs = frame.f_locals
                del frame
            elif locs is None:
                locs = globs
            exec("""exec code in globs, locs""")

    # Defined here for backward compatibility:

    def old_div(a, b):
        """
        DEPRECATED: import ``old_div`` from ``past.utils`` instead.

        Equivalent to ``a / b`` on Python 2 without ``from __future__ import
        division``.

        TODO: generalize this to other objects (like arrays etc.)
        """
        if isinstance(a, numbers.Integral) and isinstance(b, numbers.Integral):
            return a // b
        else:
            return a / b

    def as_native_str(encoding='utf-8'):
        '''
        A decorator to turn a function or method call that returns text, i.e.
        unicode, into one that returns a native platform str.

        Use it as a decorator like this::

            from __future__ import unicode_literals

            class MyClass(object):
                @as_native_str(encoding='ascii')
                def __repr__(self):
                    return next(self._iter).upper()
        '''
        if PY3:
            return lambda f: f
        else:
            def encoder(f):
                @functools.wraps(f)
                def wrapper(*args, **kwargs):
                    return f(*args, **kwargs).encode(encoding=encoding)
                return wrapper
            return encoder

    # listvalues and listitems definitions from Nick Coghlan's (withdrawn)
    # PEP 496:
    try:
        dict.iteritems
    except AttributeError:
        # Python 3
        def listvalues(d):
            return list(d.values())
        def listitems(d):
            return list(d.items())
    else:
        # Python 2
        def listvalues(d):
            return d.values()
        def listitems(d):
            return d.items()

    if PY3:
        def ensure_new_type(obj):
            return obj
    else:
        def ensure_new_type(obj):
            from future.types.newbytes import newbytes
            from future.types.newstr import newstr
            from future.types.newint import newint
            from future.types.newdict import newdict

            native_type = type(native(obj))

            # Upcast only if the type is already a native (non-future) type
            if issubclass(native_type, type(obj)):
                # Upcast
                if native_type == str:  # i.e. Py2 8-bit str
                    return newbytes(obj)
                elif native_type == unicode:
                    return newstr(obj)
                elif native_type == int:
                    return newint(obj)
                elif native_type == long:
                    return newint(obj)
                elif native_type == dict:
                    return newdict(obj)
                else:
                    return obj
            else:
                # Already a new type
                assert type(obj) in [newbytes, newstr]
                return obj

    __all__ = ['PY2', 'PY26', 'PY3', 'PYPY',
               'as_native_str', 'binary_type', 'bind_method', 'bord', 'bstr',
               'bytes_to_native_str', 'class_types', 'encode_filename',
               'ensure_new_type', 'exec_', 'get_next', 'getexception',
               'implements_iterator', 'integer_types', 'is_new_style', 'isbytes',
               'isidentifier', 'isint', 'isnewbytes', 'istext', 'iteritems',
               'iterkeys', 'itervalues', 'lfilter', 'listitems', 'listvalues',
               'lmap', 'lrange', 'lzip', 'native', 'native_bytes', 'native_str',
               'native_str_to_bytes', 'old_div',
               'python_2_unicode_compatible', 'raise_',
               'raise_with_traceback', 'reraise', 'string_types',
               'text_to_native_str', 'text_type', 'tobytes', 'viewitems',
               'viewkeys', 'viewvalues', 'with_metaclass'
               ]