6.6 Keyword arguments

Learning objectives

By the end of this section you should be able to

• Describe the difference between positional and keyword arguments.
• Create functions that use positional and keyword arguments and default parameter values.

Keyword arguments

So far, functions have been called using positional arguments, which are arguments that are assigned to parameters in order. Python also allows keyword arguments, which are arguments that use parameter names to assign values rather than order. When mixing positional and keyword arguments, positional arguments must come first in the correct order, before any keyword arguments.

    def greeting(msg, name, count):
      i = 0
      for i in range(0, count):
        print(msg, name)
    

Default parameter values

Functions can define default parameter values to use if a positional or keyword argument is not provided for the parameter. Ex: def season(m, d, hemi="N"): defines a default value of "N" for the hemi parameter. Note: Default parameter values are only defined once to be used by the function, so mutable objects (such as lists) should not be used as default values.

The physics example below calculates weight as a force in newtons given mass in kilograms and acceleration in $\frac{m}{s^2}$. Gravity on Earth is 9.8 $\frac{m}{s^2}$, and gravity on Mars is 3.7 $\frac{m}{s^2}$.

    def greeting(msg, name="Friend", count=1):
      i = 0
      for i in range(0, count):
        print(msg, name)