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# 28.4. `future_builtins` — Python 3 builtins

2.6 新版功能.

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.

注解

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()`.

  注解

  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()`.