Python Context Manager

External

• https://www.pythontutorial.net/advanced-python/python-context-managers/

Internal

• Python Language

Overview

An execution context is useful when the code uses resources that need closing, even if the code follows an unexpected execution path, like when an exception is raised.

An execution context is equivalent with the following construct:

r = Resource()
r.open()
try:
  #
  # use resource, while anywhere in this code block exception might be thrown
  #
finally:
  r.close()

The equivalent semantics using a context manager can be achieved with this syntax:

with <create-context> as ctx:
  #
  # use the context
  #

#
# at the exit from the indented block, the context is automatically cleaned up
#

How it Works

When the interpreter encounters the with statement, it creates a new context.

The context an optionally return an object, which is accessible from the indented block that follows with.