8.5. The$_{with}$ statement 99 The Python Language Reference, Release 3.9.5 8.5 The with statement manager=(EXPRESSION) enter =type(manager) .__enter__ exit =type(manager) .__exit__ value=enter(manager) hit_except = False try : TARGET =value SUITE except : hit_except = True if not exit(manager, *sys.exc_info()): raise finally : if not hit_except: exit(manager, None , None , None ) is semantically equivalent to: If the suite was exited for any reason other than an exception, the return value from$_{__exit__()}$ is ignored, and execution proceeds at the normal location for the kind of exit that was taken. The following code: If the suite was exited due to an exception, and the return value from the$_{__exit__()}$ method was false, the exception is reraised. If the return value was true, the exception is suppressed, and execution continues with the statement following the$_{with}$ statement. 7. The context manager’s$_{__exit__()}$ method is invoked. If an exception caused the suite to be exited, its type, value, and traceback are passed as arguments to$_{__exit__()}$ . Otherwise, three$_{None}$ arguments are supplied. 6. The suite is executed. Note: The with statement guarantees that if the __enter__() method returns without an error, then __exit__() will always be called. Thus, if an error occurs during the assignment to the target list, it will be treated the same as an error occurring within the suite would be. See step 6 below. 4. The context manager’s$_{__enter__()}$ method is invoked. 5. If a target was included in the$_{with}$ statement, the return value from$_{__enter__()}$ is assigned to it. 3. The context manager’s __exit__() is loaded for later use. 2. The context manager’s __enter__() is loaded for later use. 1. The context expression (the expression given in the with_item ) is evaluated to obtain a context manager. The execution of the$_{with}$ statement with one “item” proceeds as follows: The with statement is used to wrap the execution of a block with methods defined by a context manager (see section With Statement Context Managers ). This allows common try … except … finally usage patterns to be encapsulated for convenient reuse. with_stmt ::= "with" with_item ("," with_item )* ":" suite with_item ::= expression ["as" target ] with EXPRESSION as TARGET: SUITE