function_parameters.md

Function parameters

There are four types of function parameters in Python:

• obligatory parameters
• optional parameters
• list parameters (*args)
• keyword parameters (**kwargs)

The following example uses all four of them:

:::python
def example(obligatory, optional=77, *args, **kwargs):
    print("obligatory: ", obligatory)
    print("optional  : ", optional)
    print("args      : ", args)
    print("kwargs    : ", kwargs)


example(True, 99, 77, 55, a=33, b=11)

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Mutable and immutable parameters

Depending on their data type, some function parameters are mutable, others are not:

• lists, dictionaries and sets are mutable
• integers, floats, strings and tuples are immutable

Here is a small illustration:

:::python
def change(var1, var2):
    """Change two values."""
    var1 += [7]
    var2 += 7
    
    
data = [3,4,5]
number = 6

change(data, number)

print("The list now contains", data)
print("The number is now", number)