with os.scandir() raises AttributeError: __exit__

问题:

An AttributeError is raised when I use the example code from python's documentation (here). The example code is as follows:

with os.scandir(path) as it:
    for entry in it:
        if not entry.name.startswith('.') and entry.is_file():
            print(entry.name)

The result is an AttributeError:

D:\Programming>test.py
Traceback (most recent call last):
  File "D:\Programming\test.py", line 3, in <module>
    with os.scandir() as it:
AttributeError: __exit__

Although, assigning os.scandir() to a variable works fine. Could someone tell me what I'm missing?

回答1:

The context manager support was added in Python 3.6, trying to use it with previous versions will raise the error you see since it isn't a context manager (and Python tries to load __exit__ first).

This is stated in its documentation (right under the code snippet you saw) for scandir:

New in version 3.6: Added support for the context manager protocol and the close() method. [...]

^{(Emphasis mine)}

You can either update to Python 3.6 or, if you can't, don't use it as a context manager.

回答2:

The docs say

New in version 3.6: Added support for the context manager protocol

You are probably running an older Python version.