Python 2 中的 Python 3 类型提示 [英] Python 3 type hints in Python 2

问题描述

我有 python def 定义，它似乎适用于 python3:

I have python def definition which seems working for python3:

def get_default_device(use_gpu: bool = True) -> cl.Device:

在 python2 下，我收到以下语法错误:

Under python2 I get the following syntax error:

root:~/pyopencla/ch3# python map_copy.py
Traceback (most recent call last):
  File "map_copy.py", line 9, in <module>
    import utility
  File "/home/root/pyopencla/ch3/utility.py", line 6
    def get_default_device(use_gpu: bool = True) -> cl.Device:
                                  ^
SyntaxError: invalid syntax

如何让类型提示兼容python2?

How to make type hints compatible with python2?

推荐答案

PEP 3107.注释作为类型提示的用法在 Python 的 PEP 484 中正式化3.5+.

Function annotations were introduced in PEP 3107 for Python 3.0. The usage of annotations as type hints was formalized in in PEP 484 for Python 3.5+.

3.0 之前的任何版本都将根本不支持您用于类型提示的语法.但是，PEP 484 提供了一种解决方法，一些编辑可能会选择尊重它.在您的情况下，提示如下所示:

Any version before 3.0 then will not support the syntax you are using for type hints at all. However, PEP 484 offers a workaround, which some editors may choose to honor. In your case, the hints would look like this:

def get_default_device(use_gpu=True):
    # type: (bool) -> cl.Device
    ...

或更详细地说，

def get_default_device(use_gpu=True  # type: bool
                      ):
    # type: (...) -> cl.Device
    ...

PEP 明确指出，这种形式的类型提示应该适用于任何版本的 Python，如果它完全受支持的话.

The PEP explicitly states that this form of type hinting should work for any version of Python, if it is supported at all.

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