Python Functions
- 5.1 Function Definitions
- 5.2 Default Arguments
- 5.3 Variadic Arguments
- 5.4 Keyword Arguments
- 5.5 Variadic Keyword Arguments
- 5.6 Functions Accepting All Inputs
- 5.7 Positional-Only Arguments
- 5.8 Names, Documentation Strings, and Type Hints
- 5.9 Function Application and Parameter Passing
- 5.10 Return Values
- 5.11 Error Handling
- 5.12 Scoping Rules
- 5.13 Recursion
- 5.14 The lambda Expression
- 5.15 Higher-Order Functions
- 5.16 Argument Passing in Callback Functions
- 5.17 Returning Results from Callbacks
- 5.18 Decorators
- 5.19 Map, Filter, and Reduce
- 5.20 Function Introspection, Attributes, and Signatures
- 5.21 Environment Inspection
- 5.22 Dynamic Code Execution and Creation
- 5.23 Asynchronous Functions and await
- 5.24 Final Words: Thoughts on Functions and Composition
This chapter is from the book
This chapter is from the book
This chapter is from the book
Functions are a fundamental building block of most Python programs. This chapter describes function definitions, function application, scoping rules, closures, decorators, and other functional programming features. Particular attention is given to different programming idioms, evaluation models, and patterns associated with functions.
5.1 Function Definitions
Functions are defined with the def statement:
def add(x, y):
return x + y
The first part of a function definition specifies the function name and parameter names that represent input values. The body of a function is a sequence of statements that execute when the function is called or applied. You apply a function to arguments by writing the function name followed by the arguments enclosed in parentheses: a = add(3, 4). Arguments are fully evaluated left-to-right before executing the function body. For example, add(1+1, 2+2) is first reduced to add(2, 4) before calling the function. This is known as applicative evaluation order. The order and number of arguments must match the parameters given in the function definition. If a mismatch exists, a TypeError exception is raised. The structure of calling a function (such as the number of required arguments) is known as the function’s call signature.