How python creates objects that support with statements

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Create objects that support "with" statements

For example, we all know how to use the "with" statement to open a file or acquire a lock, but can we implement our own context expressions? Yes, we can use "enter" and "exit" to implement context management protocols:

Class Connection: def _ init__ (self):... Def _ _ enter__ (self): # Initialize connection... Def _ _ exit__ (self, type, value, traceback): # Close connection... With Connection () as c: # _ _ enter__ () executes... # conn.__exit__ () executes

This is the most common way to implement context management in Python, but there is a simpler way:

From contextlib import contextmanager @ contextmanager def tag (name): print (f "") yield print (f "") with tag ("H2"): print ("This is Title.")

The above code implements the content management protocol using contextmanager's manager decorator. The first part of the tag function (the part before yield) is executed when you enter the with block, then the with block is executed, and finally the rest of the tag function is executed.

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