Python functions arguments with examples

In Part 1 of the Python functions article, I gave you an introduction to Python functions. In this article, we will take a look at Python functions with arguments. Arguments allow passing some data to a function so that the function then operates on the data.

Python functions arguments are mainly of 4 types: positional, default, keyword, and arbitrary. Let us now take a look at each type of argument

Positional Arguments

Positional arguments are arguments whose values are passed in the same order in which they are specified in the function definition.

Consider the following code:

def showMarks(name,marks):    print("Hello", name,"you have scored",marks,"marks!")

This code specifies a showMarks function. It accepts arguments name and marks and simply prints a message with these values.

You can now invoke this function as follows:

showMarks("Jane",97)

This assigns the value “Jane” to the first argument that is name and the value 97 to the second argument that is marks. So, this code produces the following output:

Hello Jane you have scored 97 marks!

Keyword Arguments

Keyword arguments are those in which a keyword corresponding to the parameter name is specified in the method call.  So, in the example above, you can invoke the showMarks function as follows:

showMarks(marks=97,name="Jane")

This code specifies the name of the method parameter (marks) along with the value 97 to assign to marks. Similarly, it also specifies the name keyword with the value “Jane”. As is obvious, when you use keyword parameters, the order does not matter, so you can specify the parameters in any order.

Default

Default arguments refer to default values given to an argument. When a default value is given to an argument, you need not specify an explicit value in the method call.

We can re-write the showMarks function as follows:

def showMarks(name,marks=100):    print("Hello", name,"you have scored",marks,"marks!")

In this case, the marks argument is given a default value of 100.  So, when you invoke showMarks, there is no need to specify a value for marks. So, you can invoke it as follows:

showMarks(name="Jane")

Since this code does not pass any value for marks, the default value is used. so, this code produces the following output:

Hello Jane you have scored 100 marks!

You can also specify an explicit value for a default argument as follows:

showMarks(name="Jane", marks=97)

This code specifies the value 97 corresponding to the marks parameter. So, this code produces the following output:

Hello Jane you have scored 97 marks!

In addition, even when you use default arguments, you need not specify argument keywords in the method call, you can still pass in arguments by position as follows:

showMarks("Jane")

This assigns the value “Jane” to the first argument that is name. Since only one argument is specified, the default value for marks is used. So, this code produces the following output:

Hello Jane you have scored 100 marks!

Finally, you can also use a positional argument to override a default argument value as follows:

showMarks("Jane",97)

This assigns the value “Jane” to the first argument that is name and the value 97 to the second argument that is marks. So, this code produces the following output:

Hello Jane you have scored 97 marks!

Arbitrary

Python allows specifying a variable number of arguments to a method. These are known as arbitrary arguments. Arbitrary argument can be positional or keyword based.

Arbitrary Positional Arguments

Arbitrary positional arguments are specified with an asterisk symbol (*) in the method definition. In the method call, values are specified based on position.

We can re-write the showMarks function as follows:

def showMarks(name,*marks):    print("Hello", name,"you have scored",marks,"marks!")

This code designates marks as an arbitrary positional argument.  Thus, you can now invoke showMarks with any number of values corresponding to marks as follows:

showMarks("Jane",97,78)

This code produces the following output:

Hello Jane you have scored (97, 78) marks!

You can also invoke showMarks as follows:

showMarks("Jane",97,78,89,90)

This code produces the following output:

Hello Jane you have scored (97, 78, 89, 90) marks!

Arbitrary Keyword Arguments

Arbitrary keyword arguments are specified with a double asterisk symbol (**) in the method definition. In the method call, you need to specify a keyword corresponding to each arbitrary parameter value.

We can re-write the showMarks function as follows:

def showMarks(name,**marks):    print("Hello", name,"you have scored",marks,"marks!")

This code designates marks as an arbitrary keyword argument.  Thus, you can now invoke showMarks with any number of key-values corresponding to marks as follows:

showMarks(name="Jane",English=97,Maths=89)

This code specifies a different keyword ( the name of the subject) corresponding to each marks value. So, it specifies English with the value 97 and Maths with the value 89. Similarly, it also specifies the name keyword with the value “Jane”. Like ordinary keyword parameters, the order does not matter, so you can specify the parameters in any order.

This code produces the following output:

Hello Jane you have scored {'english': 97, 'maths': 89} marks!

Further Learning

The Python Masterclass
Everything you need to know about Python
Python for beginners
Python for finance

Conclusion

So just to summarize, Python supports 4 different type of arguments. These are positional (values are passed by position), keyword-based (keyword corresponding to each parameter name is specified), default (in which a default value is given to each argument) and arbitrary (in which a variable number of values can be passed to an argument).

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