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"""
A selection of cross-compatible functions for Python 2 and 3.
These come from several sources:
* Jinja2 (BSD licensed: see https://github.com/mitsuhiko/jinja2/blob/master/LICENSE
* Pandas compatibility module pandas.compat
* six.py by Benjamin Peterson
* Django
This exports useful functions for 2/3 compatible code that are not
builtins on Python 3:
* 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
* Uses the original method if available, otherwise uses 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.
This module also defines a simple decorator called
``python_2_unicode_compatible`` (from django.utils.encoding) which
defines ``__unicode__`` and ``__str__`` methods consistently under Python
3 and 2. To support Python 3 and 2 with a single code base, simply define
a ``__str__`` method returning unicode text and apply the
python_2_unicode_compatible 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))
On Python 3, this decorator is a no-op.
"""
import types
import sys
import numbers
PY3 = sys.version_info[0] == 3
PY2 = sys.version_info[0] == 2
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 it does nothing.
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.
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 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
else:
# Python 2
def bchr(s):
return chr(s)
def bstr(s):
return str(s)
def bord(s):
return ord(s)
###
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):
'''
Encodes to latin-1 (where the first 256 chars are the same as
ASCII.)
'''
if isinstance(s, unicode):
return s.encode('latin-1')
else:
return ''.join(s)
if PY3:
def native_str_to_bytes(s, encoding='ascii'):
return s.encode(encoding)
def bytes_to_native_str(b, encoding='ascii'):
return b.decode(encoding)
else:
# Python 2
def native_str_to_bytes(s, encoding='ascii'):
return s
def bytes_to_native_str(b, encoding='ascii'):
return b
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 bound/unbound method issue
if not PY3:
setattr(cls, name, types.MethodType(func, None, cls))
else:
setattr(cls, name, func)
def getexception():
return sys.exc_info()[1]
def reraise(tp, value=None, tb=None):
"""
Create a raise_ method that allows re-raising exceptions with the cls
value and traceback on Python2 & Python3.
"""
if PY3:
if value.__traceback__ is not tb:
raise value.with_traceback(tb)
raise value
else:
exec('def reraise(tp, value=None, tb=None):\n raise tp, value, tb')
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, isinstance
"""
return isinstance(obj, type(u''))
def isbytes(obj):
"""
Deprecated. Use::
isinstance(obj, bytes)
after this import:
>>> from future.builtins import bytes, isinstance
"""
return isinstance(obj, type(b''))
def isint(obj):
"""
Tests whether an object is a Py3 ``int`` or either a Py2 ``int`` or
``long``.
Instead of using this function, you can use the following idiom:
isinstance(obj, numbers.Integral)
or simply:
isinstance(obj, int)
after this import:
from future.builtins import int, isinstance
"""
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 future.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
def old_div(a, b):
"""
Equivalent to ``a / b`` on Python 2 without ``from __future__ import
division``.
"""
return a // b if (isint(a) and isint(b)) else a / b
__all__ = ['PY3', 'PY2', 'PYPY', 'python_2_unicode_compatible',
'with_metaclass', 'bchr', 'bstr', 'bord',
'tobytes', 'str_to_native_bytes', 'bytes_to_native_str',
'lrange', 'lmap', 'lzip', 'lfilter',
'isidentifier', 'iteritems', 'iterkeys', 'itervalues',
'viewitems', 'viewkeys', 'viewvalues',
'bind_method', 'getexception',
'reraise', 'implements_iterator', 'get_next', 'encode_filename',
'is_new_style', 'native_str']