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Arbitrary Arguments

Updated Oct 29, 2019 ·

Overview​

Functions in Python need specific arguments, but we can make them more flexible. The following are different ways to handle function arguments.

Fixed Arguments​

A function expects a set number of arguments. If we pass the wrong type or too many, it will cause an error.

  • A function designed for a list or set won't work with a dictionary.
  • Passing multiple separate values instead of a single list causes an error.

Example:

def average(values):
    return sum(values) / len(values)

print(average(10, 20, 30))  # Error: Too many arguments

Arbitrary Positional Arguments (*args)​

We can allow any number of arguments by using an asterisk (*).

  • The function collects all arguments into a tuple.
  • We can pass one, five, or even a thousand values.
  • The standard name is *args, but any name works.

Example:

def average(*args):
    return sum(args) / len(args)

print(average(10, 20, 30))  # Output: 20.0

Passing Multiple Lists​

Python treats *args as a single tuple. If we pass multiple lists, they can be merged automatically.

Example:

def combine(*args):
    return args  # Returns a tuple of inputs

print(combine([1, 2], [3, 4]))  # Output: ([1, 2], [3, 4])

Arbitrary Keyword Arguments (**kwargs)​

If we want to pass named arguments, we use **.

  • The function collects arguments into a dictionary.
  • The standard name is **kwargs, but any name works.
  • We can access values using .values().

Example:

def average(**kwargs):
    return sum(kwargs.values()) / len(kwargs)

print(average(a=10, b=20, c=30))  # Output: 20.0

Passing a Dictionary​

Instead of passing key-value pairs manually, we can use ** before a dictionary.

Example:

def average(**kwargs):
    return sum(kwargs.values()) / len(kwargs)

data = {'a': 10, 'b': 20, 'c': 30}
print(average(**data))  # Output: 20.0

Combining Multiple **kwargs​

We can pass multiple keyword argument dictionaries using **.

Example:

def average(**kwargs):
    return sum(kwargs.values()) / len(kwargs)
    
data1 = {'a': 10, 'b': 20}
data2 = {'c': 30, 'd': 40}

print(average(**data1, **data2))  # Output: 25.0