Python Functions: Return None, Return, or No Return Statement—Which Should You Use?

Python Functions: Delving into Return Statements

Many Python programmers face the dilemma of choosing between using return None, return, or no return statement at all when writing functions. This article explores the subtle differences among these approaches and provides guidance on when each is appropriate.

The Function Trio:

Consider the following three functions:

def my_func1():
  print("Hello World")
  return None

def my_func2():
  print("Hello World")
  return

def my_func3():
  print("Hello World")

At first glance, all three functions appear to return None. However, upon closer examination, there are nuanced differences in their behavior.

Using return None:

This explicitly indicates that the function is designed to return a value, in this case None. This value can be subsequently utilized elsewhere in the code. return None is typically employed when there is a specific return value that the function is intended to provide.

For instance, the following function returns a person's mother if they are human, and None otherwise:

def get_mother(person):
    if is_human(person):
        return person.mother
    else:
        return None

Using return:

This functions similarly to break statements in loops. It primarily serves to terminate the function execution, with the return value being inconsequential. While not frequently needed, return can be useful in specific scenarios.

Consider this example, where we search for a prisoner with a knife among a group of prisoners:

def find_prisoner_with_knife(prisoners):
    for prisoner in prisoners:
        if "knife" in prisoner.items:
            prisoner.move_to_inquisition()
            return  # No need to check the remaining prisoners or raise an alert
    raise_alert()

Note that the function's return value should not be assigned to a variable, as it is not intended for further use.

Using No return Statement:

This approach also returns None, but it implies that the function has successfully finished without any specific return value. It essentially fulfills the same role as return in void functions in languages like C or Java.

def set_mother(person, mother):
    if is_human(person):
        person.mother = mother

Conclusion:

While all three methods ultimately return None, they serve distinct purposes. return None is employed when a specific return value needs to be conveyed. return is used to explicitly terminate function execution, and using no return statement indicates a successfully completed function without a specified return value.

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