- 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
5.6 Functions Accepting All Inputs
By using both * and **, you can write a function that accepts any combination of arguments. The positional arguments are passed as a tuple and the keyword arguments are passed as a dictionary. For example:
# Accept variable number of positional or keyword arguments
def func(*args, **kwargs):
# args is a tuple of positional args
# kwargs is dictionary of keyword args
...
This combined use of *args and **kwargs is commonly used to write wrappers, decorators, proxies, and similar functions. For example, suppose you have a function to parse lines of text taken from an iterable:
def parse_lines(lines, separator=',', types=(), debug=False):
for line in lines:
...
statements
...
Now, suppose you want to make a special-case function that parses data from a file specified by filename instead. To do that, you could write:
def parse_file(filename, *args, **kwargs):
with open(filename, 'rt') as file:
return parse_lines(file, *args, **kwargs)
The benefit of this approach is that the parse_file() function doesn’t need to know anything about the arguments of parse_lines(). It accepts any extra arguments the caller provides and passes them along. This also simplifies the maintenance of the parse_file() function. For example, if new arguments are added to parse_lines(), those arguments will magically work with the parse_file() function too.