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python with

By: Ashley J in Python Tutorials on 2017年09月27日 [フレーム]

Python with statement is used when you want to execute a block of code based on another operation. For example you need to open a file, for manipulating the file, then close it after you have worked with the file. In this case, python with is used to make sure that the file is closed after processing the file.

with open('file1.txt', 'w') as f:

  f.write('After writing this sentence to
the file, the with statement will automatically close this file1.txt')

The above with statement will automatically close the file after the nested block of code. The advantage of using a with statement is that it is guaranteed to close the file no matter how the nested block exits. If an exception occurs before the end of the block, it will close the file before the exception is caught by an outer exception handler. If the nested block were to contain a return statement, or a continue or break statement, the with statement would automatically close the file in those cases, too. It is something similar to the 'using' statement in VB.NET and C#. It allows you to ensure that a resource is "cleaned up" when the code that uses it finishes running, even if exceptions are thrown.

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