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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
        * binary_type: str in Python 2, bythes in Python 3
        * string_types: basestring in Python 2, str 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
    * Pandas compatibility module pandas.compat
    * by Benjamin Peterson
    * Django

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

PY3 = sys.version_info[0] == 3
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')

[docs]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
[docs]def with_metaclass(meta, *bases): """ Function from jinja2/ 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 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
[docs] 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
[docs] 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 = lmap = lfilter = __builtin__.filter
[docs]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))
[docs]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)
[docs]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)
[docs]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)
[docs]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)
[docs]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)
[docs]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)
[docs]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)
[docs] 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 value is not None and isinstance(tp, Exception): raise TypeError("instance exception may not have a separate value") if value is not None: exc = tp(value) else: exc = tp if exc.__traceback__ is not tb: raise exc.with_traceback(tb) raise exc
[docs] 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.__suppress_context__ = True elif cause is None: e.__cause__ = None e.__suppress_context__ = True elif isinstance(cause, BaseException): e.__cause__ = cause 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_
[docs]def implements_iterator(cls): ''' From jinja2/ 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__ del cls.__next__ return cls
if PY3: get_next = lambda x: 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
[docs]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
[docs]def istext(obj): """ Deprecated. Use:: >>> isinstance(obj, str) after this import: >>> from future.builtins import str """ return isinstance(obj, type(u''))
[docs]def isbytes(obj): """ Deprecated. Use:: >>> isinstance(obj, bytes) after this import: >>> from future.builtins import bytes """ return isinstance(obj, type(b''))
[docs]def isnewbytes(obj): """ Equivalent to the result of ``isinstance(obj, newbytes)`` were ``__instancecheck__`` not overridden on the newbytes subclass. In other words, it is REALLY a newbytes instance, not a Py2 native str object? """ # TODO: generalize this so that it works with subclasses of newbytes # Import is here to avoid circular imports: from future.types.newbytes import newbytes return type(obj) == newbytes
[docs]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)
[docs]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:
[docs]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
[docs]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', 'bind_method', 'bord', 'bstr', 'bytes_to_native_str', 'encode_filename', 'ensure_new_type', 'exec_', 'get_next', 'getexception', 'implements_iterator', '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', 'text_to_native_str', 'tobytes', 'viewitems', 'viewkeys', 'viewvalues', 'with_metaclass' ]