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Functions with Default Arguments

Functions with Default Arguments

Functions can be specified with default arguments. If values for these arguments are not supplied when the function is called, the default values are used. The general format to define a function with default arguments is below:

def function_name(argument1=default_value, argument2=default_value):
    return output

An example a function with default arguments might be a function that calculates the distance an object falls based on time. The general formula for fall distance d based on fall time t can be modeled as:

d = \frac{1}{2}gt^2

Where g is the acceleration due to gravity. On earth the value of g = 9.81 m/s^2. But on the moon, g = 1.625 m/s^2. Our falldist() function will include the default value for earth's gravity and give programmers the option of specifying a different value for g if they choose.

In [1]:
def falldist(t, g=9.81):
    d = 0.5  g  t**2
    return d

On earth, the distance a ball that falls for three seconds is calculated by falldist(3). In the function call falldist(3), no value is specified for g, so the default value 9.81 is used.
In [2]:


On earth, the ball falls 44.145 meters in 3 seconds.

However, on the moon gravity is much weaker than on earth. The acceleration of falling objects on the moon is g = 1.625 m/s^2. To calculate how far a ball falls on the moon in three seconds, two arguments need to be supplied to the falldist() function: 3 and 1.625. If a second argument is provided to the falldist() function, in this case 1.625, it overrides the default value assigned in the first line of the function.

In [3]:
falldist(3, 1.625)


On the moon, the ball falls 7.3125 meters in 3 seconds.