Extend vs += Behaviour

Question

Help me understand the problem I am failing to identify in the following code.

def extend_a_list(list_var):
    return list_var.extend([6, 2])

def plus_equals_list(list_var):
    list_var += [6]
    return list_var

list_var = [1, 2, 3]
print "Extending"
print extend_a_list(list_var)

list_var = [1, 2, 3]
print "Plus Equals"
print plus_equals_list(list_var)


>>> Extending
>>> None
>>> Plus Equals
>>> [1, 2, 3, 6]

Extend is giving None. Why is that?

https://docs.python.org/2/library/stdtypes.html#mutable-sequence-types - `extend()` does not return anything. — Brian Cain, Mar 25 '15 at 14:58

Mathias711 · Accepted Answer · 2015-03-25T15:08:56.633

5

Extend returns nothing, it modifies the inputted list:

a = [1,2,3]
# a = [1,2,3]
b = a.extend([4])
# a = [1,2,3,4]
# b = None

edited Mar 25 '15 at 15:08

answered Mar 25 '15 at 14:57

Mathias711

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Extend vs += Behaviour

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