Part Three: Functions: Arguments, default parameters, docstrings

We can also use default parameter values in our user-defined functions. Looking at our last example, we could assign a default value for the parameter b, say b = 5. This value would be used unless an argument is provided to overwrite it when the function is called. Example

def addition(a, b = 5):
    return a + b

print(addition(2))

This would give 7.

 

def addition(a, b = 5):
    return a + b

print(addition(2, 8))

This would give 10.

 

 We could have as many parameters as required. However, the default parameters always come after the positional parameters have been specified so we do not get error messages when we run our code.

 

def addition(a, b, c = 3, d = 4):
    return a + b + c + d

print(addition(2, 8))

This would give 17.

 

If we do not know how many parameters and hence, how many arguments the function would take, we could use the (*args). For example

 

def addition(*num):

   for a in num:
        return sum(num)

print(addition(1, 2, 3, 4, 5, 6, 7, 8))

This would be 36.

 

Lastly, let us discuss what docstrings are in relation to functions. They are optional documentation a bit similar to comments but they provide documentation for what your user-defined function does so others can read up on it especially for complex programs. They are enclosed within triple quotation marks. Example

 

def addition(*num):

            '''This function performs addition of all the arguments provided to it'''

 

   for a in num:
        return sum(num)

print(addition(1, 2, 3, 4, 5, 6, 7, 8))

When we now run

            print(addition.__doc__)

The docstring we included would be printed.

 

We could try it for inbuilt functions like print and input too.

            print(print.__doc__)

            print(input.__doc__)

We can now update our calculator program.