Skip to ContentGo to accessibility pageKeyboard shortcuts menu
OpenStax Logo

Highlights from this chapter include:

  • Functions are named blocks of code that perform tasks when called and make programs more organized and optimized.
  • Control flow is the sequence of program execution. Control flow moves between calling code and function code when a function is called.
  • Variable scope refers to where a variable can be accessed. Global variables can be accessed anywhere in a program. Local variables are limited in scope, such as to a function.
  • Parameters are function inputs defined with the function. Arguments are values passed to the function as input by the calling code. Parameters are assigned with the arguments' values.
  • Function calls can use positional arguments to map values to parameters in order.
  • Function calls can use keyword arguments to map values using parameter names in any order.
  • Functions can define default parameter values to allow for optional arguments in function calls.
  • Python uses a pass-by-object-reference system to assign parameters with the object values referenced by the arguments.
  • Functions can use return statements to return values back to the calling code.

At this point, you should be able to write functions that have any number of parameters and return a value, and programs that call functions using keyword arguments and optional arguments.

Construct Description
Function definition
def function_name():
  # Function body
def function_name(parameter_1):
  # Function body
def function_name(parameter_1):
  # Function body
Return statement
def function_name():
  # Function body
  return result # Returns the value of result to the caller
Variables (scope)
def function_name(parameter_1):
  # Function body
  local_var = parameter_1 * 5
  return local_var

global_var = function_name(arg_1)
Keyword arguments
def function_name(parameter_1, parameter_2):
  # Function body
function_name(parameter_2 = 5, parameter_1 = 2)
Default parameter value
def function_name(parameter_1 = 100):
  # Function body
Table 6.2 Chapter 6 reference.

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Attribution information
  • If you are redistributing all or part of this book in a print format, then you must include on every physical page the following attribution:
    Access for free at
  • If you are redistributing all or part of this book in a digital format, then you must include on every digital page view the following attribution:
    Access for free at
Citation information

© Mar 15, 2024 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.

This book utilizes the OpenStax Python Code Runner. The code runner is developed by Wiley and is All Rights Reserved.