bpo-6519: Improve Python Input Output Tutorial (GH-2143) (GH-2145) · python/cpython@81c05cc (original) (raw)
`@@ -262,6 +262,35 @@ to file data is fine for text files, but will corrupt binary data like that in
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`` :file:JPEG or :file:EXE files. Be very careful to use binary mode when
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`reading and writing such files.
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``
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It is good practice to use the :keyword:with keyword when dealing
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with file objects. The advantage is that the file is properly closed
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after its suite finishes, even if an exception is raised at some
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point. Using :keyword:with is also much shorter than writing
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equivalent :keyword:try\ -\ :keyword:finally blocks::
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with open('workfile') as f:
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... read_data = f.read()
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f.closed
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True
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If you're not using the :keyword:with keyword, then you should call
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``f.close()`` to close the file and immediately free up any system
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resources used by it. If you don't explicitly close a file, Python's
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garbage collector will eventually destroy the object and close the
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open file for you, but the file may stay open for a while. Another
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risk is that different Python implementations will do this clean-up at
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different times.
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After a file object is closed, either by a :keyword:with statement
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or by calling ``f.close()``, attempts to use the file object will
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automatically fail. ::
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f.close()
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f.read()
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Traceback (most recent call last):
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File "", line 1, in
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ValueError: I/O operation on closed file
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`.. _tut-filemethods:
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``
``` @@ -354,27 +383,6 @@ to the very file end with seek(0, 2)) and the only valid offset values are
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``` those returned from the ``f.tell()``, or zero. Any other *offset* value produces
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`undefined behaviour.
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``
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When you're done with a file, call ``f.close()`` to close it and free up any
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system resources taken up by the open file. After calling ``f.close()``,
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attempts to use the file object will automatically fail. ::
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``
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f.close()
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``
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f.read()
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``
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Traceback (most recent call last):
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``
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File "", line 1, in
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ValueError: I/O operation on closed file
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``
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`` -
It is good practice to use the :keyword:with keyword when dealing with file
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objects. This has the advantage that the file is properly closed after its
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suite finishes, even if an exception is raised on the way. It is also much
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shorter than writing equivalent :keyword:try\ -\ :keyword:finally blocks::
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``
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``
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with open('workfile', 'r') as f:
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``
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... read_data = f.read()
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f.closed
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True
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``
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`` File objects have some additional methods, such as :meth:~file.isatty and
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`` :meth:~file.truncate which are less frequently used; consult the Library
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`Reference for a complete guide to file objects.
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