"""
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)
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
# 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
[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 = __builtin__.zip
lmap = __builtin__.map
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 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
[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.__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_
[docs]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
[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 ``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'
[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', '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'
]
