Using context managers

Writing Functions in Python

Shayne Miel

Software Architect @ Duo Security

What is a context manager?

A context manager:

Sets up a context
Runs your code
Removes the context

A catered party

empty room

A catered party

room catered

A catered party

room party

A catered party

room catered

A catered party

empty room

Catered party as context

Context managers:

Set up a context
Run your code
Remove the context

Caterers:

Set up the tables with food and drink
Let you and your friends have a party
Cleaned up and removed the tables

A real-world example

with open('my_file.txt') as my_file:
  text = my_file.read()
  length = len(text)

print('The file is {} characters long'.format(length))

open() does three things:

Sets up a context by opening a file
Lets you run any code you want on that file
Removes the context by closing the file

Using a context manager

with

Using a context manager

with <context-manager>()

Using a context manager

with <context-manager>(<args>)

Using a context manager

with <context-manager>(<args>):

Using a context manager

with <context-manager>(<args>):
  # Run your code here
  # This code is running "inside the context"

Using a context manager

with <context-manager>(<args>):
  # Run your code here
  # This code is running "inside the context"

# This code runs after the context is removed

Using a context manager

with <context-manager>(<args>) as <variable-name>:
  # Run your code here
  # This code is running "inside the context"

# This code runs after the context is removed

with open('my_file.txt') as my_file:
  text = my_file.read()
  length = len(text)

print('The file is {} characters long'.format(length))

Let's practice!

Writing Functions in Python