Python `return`, `return None`, and No `return`: What are the Key Differences?

Return, Return None, and No Return in Python: What's the Difference?

Consider the following functions:

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

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

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

While they may appear to all return None, there are subtle differences in their behavior.

Behavior Differences

When these functions are executed:

• my_func1(): Prints "Hello World" and explicitly returns None.
• my_func2(): Prints "Hello World" and implicitly returns None (the default behavior of functions).
• my_func3(): Prints "Hello World" and returns nothing (not even None).

Usage Considerations

Return None

• Use for functions that are intended to return a value, even if it's None.
• The returned value can be used or ignored later in the code.
• Avoid returning None if there are no alternative return values.

Return

• Use to explicitly exit a function, similar to break statements in loops.
• The return value is irrelevant and should not be used.
• Useful when you only want to exit the function without returning a specific value.

No Return

• Use for functions that do not need to return any value or simply indicate successful execution.
• Like return, the returned value is not meant to be used or captured.
• Similar to void functions in other languages like C and Java.

Examples

Getting a Mother's Name (Return None):

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

Finding a Prisoner with a Knife (Return):

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 other prisoners.
    raise_alert()

Setting a Mother's Name (No Return):

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

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