Python Custom Functions

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Index

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Mutable data types as default parameter

It’s highly suggested to not use mutable objects as default functions parameters, in fact they are prone to hard to identify errors

def add_to(num, target=[]):
	target.append(num)
	return target
 
add_to(1) # expected_Output: [1] # real_Output: [1]
add_to(2) # expected_Output: [2] # real_Output: [1,2]
add_to(3) # expected_Output: [3] # real_Output: [1,2,3]
 

How resolve this problem:

def add_to(num, target=None):
	if target is None:
		target = []
	
	target.append(num)
	return target
 
add_to(1) # expected_Output: [1] # real_Output: [1]
add_to(2) # expected_Output: [2] # real_Output: [2]
add_to(3) # expected_Output: [3] # real_Output: [3]

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