Chapter 5

Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

Chapter 5

Functions


Overview


Function Declaration


Parameters


Parameters


Positional Arguments


Keyword Arguments


Default Arguments


Return Values


Return Values If a return statement omits a return value, None is returned implicitly.

Likewise, if a function reaches the end of its evaluation without reaching a return statement, the function also returns None.


Docstrings


Docstrings


Docstring Conventions

• As a matter of consistency always use triple quotes for docstrings even if it is a one line string,

• The docstring summary should begin with an action verb (e.g., “Return this..”, “Do that..”)

• The docstring summary should end with a period. • For multi-line documentation, the docstring should

begin with a one line summary, then one blank line, and then the longer documentation.


ScopePython has three different kinds of scope:

1. the built-in scope, which is made up identifiers defined by Python, 2. the global scope, which is made up identifiers defined in a Python file but not

within a function, and 3. the function scope, which is made up identifiers (including parameters) defined in a

function.

Consider this simple example where these three different scopes are being used:


Scope

A visualization of the three principle scopes in Python - built-in identifiers form the outermost scope followed by global identifiers and function identifiers.


Scope


Scope

In this example the function scope has a variable x which shadows the global scope. The result is two different variables that happen to have the same name.


Scope


Code Repetition


Code Repetition


Code Repetition


Code Repetition


Top-Down Design


Top-Down Design


Top-Down Design


Top-Down Design


Top-Down Design

1. If we break the problem up into smaller parts, we clarify the tasks that need to be done to solve the problem.

2. Each smaller part is typically less complicated than the whole, making the problem more approachable.

3. Smaller parts may be reusable, reducing the implementation size.

4. Breaking the problem up also allows us to distribute the problem solving work, enabling team work.


Recursion


Recursion


Functions as Values


Functions as Values

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Chapter 5