Best practices for writing functions - Confused with output


Can you please help with the second output? Since we are passing the default argument as var=, why it is taking var=[1] in the second print statement?

Here you are using a mutable object list as default parameter so it will keep same scope for multiple function call also.

You can read more detail in doc here

Default parameter values are evaluated from left to right when the function definition is executed. This means that the expression is evaluated once, when the function is defined, and that the same “pre-computed” value is used for each call. This is especially important to understand when a default parameter is a mutable object, such as a list or a dictionary: if the function modifies the object (e.g. by appending an item to a list), the default value is in effect modified. This is generally not what was intended. A way around this is to use None as the default, and explicitly test for it in the body of the function, e.g.:

def whats_on_the_telly(penguin=None):
    if penguin is None:
        penguin = []
    penguin.append("property of the zoo")
    return penguin
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