append() and extend() in Python

Append: Adds its argument as a single element to the end of a list. The length of the list increases by one.

syntax: 
# Adds an object (a number, a string or a 
# another list) at the end of my_list
my_list.append(object)
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my_list = ['geeks', 'for']
my_list.append('geeks')
print my_list

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Output:

['geeks', 'for', 'geeks']

NOTE: A list is an object. If you append another list onto a list, the parameter list will be a single object at the end of the list.

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my_list = ['geeks', 'for', 'geeks']
another_list = [6, 0, 4, 1]
my_list.append(another_list)
print my_list

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Output:

['geeks', 'for', 'geeks', [6, 0, 4, 1]]

 



extend(): Iterates over its argument and adding each element to the list and extending the list. The length of the list increases by number of elements in it’s argument.

syntax: 
# Each element of an iterable gets appended 
# to my_list
my_list.extend(iterable) 
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my_list = ['geeks', 'for']
another_list = [6, 0, 4, 1]
my_list.extend(another_list)
print my_list

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Output:

['geeks', 'for', 6, 0, 4, 1]

NOTE: A string is an iterable, so if you extend a list with a string, you’ll append each character as you iterate over the string.

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my_list = ['geeks', 'for', 6, 0, 4, 1]
my_list.extend('geeks')
print my_list

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Output:

['geeks', 'for', 6, 0, 4, 1, 'g', 'e', 'e', 'k', 's']

Time Complexity:
Append has constant time complexity i.e.,O(1).
Extend has time complexity of O(k). Where k is the length of list which need to be added.




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