“with io.open”会自动关闭文件吗？

Question

For example:

with io.open('Example.txt','r',encoding='utf-8') as temp:
    ExampleText=temp.readlines()[1]

Do I need to close it manually, like:

with io.open('Example.txt','r',encoding='utf-8') as temp:
    ExampleText=temp.readlines()[1]
temp.close()

Answer 1

TL;DR: No, you don't need to close the stream when used with the with statement.

The reason for this is that the TextIOWrapper object returned by io.open is a context manager which will call close on the underlying file when a context is exited.

To verify this behavior we can simply call __exit__ explicitly and then try to read the file:

>>> import io
>>> foo = io.open("foo.txt", "w+")
>>> foo.__exit__()
>>> foo.read()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: I/O operation on closed file.

Which demonstrates that the file is in fact closed when __exit__ is called, which happens automatically when the with block is exited.

Note that there is one case where the file descriptor will not be closed on __exit__ and that is the case where a file-descriptor is passed to io.open rather than a file name or object along with a value of False for the closefd argument:

>>> import os
>>> file_ = open("foo.txt", "w+")
>>> foo = io.open(file_.fileno(), closefd=False)
>>> foo.__exit__()
>>> # the IOTextWrapper is closed
>>> foo.read()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: I/O operation on closed file.
>>> # but the underlying file descriptor is not closed.
>>> os.read(file_.fileno(), 512)
b''

If you pass a value of True for the closefd argument than the passed file descriptor is closed on context exit:

>>> with io.open(file_.fileno(), closefd=True):
...     pass
>>> os.read(file_.fileno(), 512)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 9] Bad file descriptor

Docs describing this behavior in detail can be found here .

Answer 2

不，您不需要手动关闭它。

Answer 3

From the reference ,

If a file descriptor is given, it is closed when the returned I/O object is closed, unless closefd is set to False.

So if you provide a file descriptor and want to manually close it (because you might use descriptor later) you call it as

import os
import io
fd = os.open("foo.txt", os.O_RDONLY)
io.open(fd, 'r', encoding='utf-8', closefd=False)