Home » Python

Python Different ways to define and call user-defined functions

Last Updated : April 22, 2025

The following are the different ways to define and call a user-defined function:

1. Define first and then call
2. Calling before define
3. Function calling inside another function
4. Define main as starting point

1. Define first and then call

The standard way to define and call a function in Python is to first write the function definition and then use it wherever you want.

Example

In the below example, we are defining a function hi() that prints "Hi" and then calling the function to execute the print statement:

#Function Defination
def hi():
    print("Hi")

#Function Calling
hi()

Output

Hi

2. Calling before define – but it will not work

If you call a function before defining it will generate a NameError. This is of defining and calling a function is incorrect.

Example

In the below example, we are calling the function hi() before it is defined, which will result in an error, as functions must be defined before calling them in Python:

# Function Calling
hi()

# Function Definition
def hi():
    print("Hi")

Output

    hi()
NameError: name 'hi' is not defined	

3. Function calling inside another function

A function can also be called inside another function.

Example

In the below example, we are defining a function hi() that prints "Hi", and then calling it inside the main() function. The main() function is executed, which in turn calls hi(), and the output is "Hi":

def main():
    hi()

def hi():
    print("Hi")

main()

Output

Hi

4. Define main as starting point

You can also define a function as starting calling function in Python. This example shows how you can define a function as the starting point.

Example

In the below example, we are defining the main() function to call the hi() function, and then using the if __name__ == "__main__": construct to ensure that the main() function is only called when the script is executed directly:

def main():
    hi()

def hi():
    print("Hi")

if __name__=="__main__":
    main()

Output

Hi

Python Define and Call Function Exercise

Select the correct option to complete each statement about defining and calling functions in Python.

1. In Python, you define a function using the ___ keyword followed by the function name and parameters. --Select-- def function func
2. To call a function in Python, you use the function's ___ followed by parentheses. --Select-- name signature reference
3. When calling a function, if it has parameters, you must pass the ___ that match the order and type of the parameters. --Select-- arguments values names

Check Answers