28.4. "future_builtins" — Python 3 builtins
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2.6 版新加入.

This module provides functions that exist in 2.x, but have different
behavior in Python 3, so they cannot be put into the 2.x builtins
namespace.

Instead, if you want to write code compatible with Python 3 builtins,
import them from this module, like this:

   from future_builtins import map, filter

   ... code using Python 3-style map and filter ...

The *2to3* tool that ports Python 2 code to Python 3 will recognize
this usage and leave the new builtins alone.

備註: The Python 3 "print()" function is already in the builtins,
  but cannot be accessed from Python 2 code unless you use the
  appropriate future statement:

     from __future__ import print_function

Available builtins are:

future_builtins.ascii(object)

   Returns the same as "repr()".  In Python 3, "repr()" will return
   printable Unicode characters unescaped, while "ascii()" will always
   backslash-escape them.  Using "future_builtins.ascii()" instead of
   "repr()" in 2.6 code makes it clear that you need a pure ASCII
   return value.

future_builtins.filter(function, iterable)

   Works like "itertools.ifilter()".

future_builtins.hex(object)

   Works like the built-in "hex()", but instead of "__hex__()" it will
   use the "__index__()" method on its argument to get an integer that
   is then converted to hexadecimal.

future_builtins.map(function, iterable, ...)

   Works like "itertools.imap()".

   備註: In Python 3, "map()" does not accept "None" for the
     function argument.

future_builtins.oct(object)

   Works like the built-in "oct()", but instead of "__oct__()" it will
   use the "__index__()" method on its argument to get an integer that
   is then converted to octal.

future_builtins.zip(*iterables)

   Works like "itertools.izip()".
