List¶
In Python, extend() and append() are methods used to add elements to a list, but they work in different ways. Here's a detailed comparison:
METHODS¶
append() Method¶
- Functionality: Adds a single element (object) to the end of the list.
- Effect: Treats the argument as a single item and appends it directly.
Example¶
# Using append
my_list = [1, 2, 3]
my_list.append(4)
print(my_list) # Output: [1, 2, 3, 4]
# Appending a list (nested list)
my_list.append([5, 6])
print(my_list) # Output: [1, 2, 3, 4, [5, 6]]
Note: If you append another list, it gets added as a single element, resulting in a nested list.
extend() Method¶
- Functionality: Adds all the elements of an iterable (e.g., list, tuple, string) to the end of the list.
- Effect: Iterates over the argument and appends each element to the list individually.
Example¶
# Using extend
my_list = [1, 2, 3]
my_list.extend([4, 5])
print(my_list) # Output: [1, 2, 3, 4, 5]
# Extending with a string (iterable)
my_list.extend("67")
print(my_list) # Output: [1, 2, 3, 4, 5, '6', '7']
Note: If you pass a list to
extend, its elements are added individually, not as a nested list.
Key Differences¶
| Aspect | append() |
extend() |
|---|---|---|
| Type of argument | Any object (single element) | Iterable (list, tuple, string, etc.) |
| Behavior | Adds the argument as a single item. | Adds each element of the argument. |
| Nested lists | Creates a nested list when a list is appended. | Merges elements into the original list. |
| Use case | Add one item or object to the list. | Add multiple elements from an iterable. |
When to Use Which¶
- Use
append()when you want to add a single element (e.g., an integer, string, or even a list as a nested list). - Use
extend()when you want to combine another iterable's elements into your list.
Comparison Example¶
# Append vs Extend
list1 = [1, 2, 3]
list1.append([4, 5]) # Adds as a single element (nested list)
print(list1) # Output: [1, 2, 3, [4, 5]]
list2 = [1, 2, 3]
list2.extend([4, 5]) # Adds elements individually
print(list2) # Output: [1, 2, 3, 4, 5]
Summary¶
- Use
append()for adding a single object. - Use
extend()for adding multiple elements.
36. Python Program to Add Two Matrices¶
# Program to add two matrices using nested loop
X = [[12,7,3],
[4 ,5,6],
[7 ,8,9]]
Y = [[5,8,1],
[6,7,3],
[4,5,9]]
result = [[0,0,0],
[0,0,0],
[0,0,0]]
# iterate through rows
for i in range(len(X)):
# iterate through columns
for j in range(len(X[0])):
result[i][j] = X[i][j] + Y[i][j]
for r in result:
print(r)
# Program to add two matrices using list comprehension
X = [[12,7,3],
[4 ,5,6],
[7 ,8,9]]
Y = [[5,8,1],
[6,7,3],
[4,5,9]]
result = [[X[i][j] + Y[i][j] for j in range(len(X[0]))] for i in range(len(X))]
for r in result:
print(r)
37. Python Program to Transpose a Matrix¶
# Program to transpose a matrix using a nested loop
X = [[12,7],
[4 ,5],
[3 ,8]]
result = [[0,0,0],
[0,0,0]]
# iterate through rows
for i in range(len(X)):
# iterate through columns
for j in range(len(X[0])):
result[j][i] = X[i][j]
for r in result:
print(r)
''' Program to transpose a matrix using list comprehension'''
X = [[12,7],
[4 ,5],
[3 ,8]]
result = [[X[j][i] for j in range(len(X))] for i in range(len(X[0]))]
for r in result:
print(r)
38. Python Program to Multiply Two Matrices¶
Matrix Multiplication using Nested Loop
Program to multiply two matrices using nested loops
# 3x3 matrix
X = [[12,7,3],
[4 ,5,6],
[7 ,8,9]]
# 3x4 matrix
Y = [[5,8,1,2],
[6,7,3,0],
[4,5,9,1]]
# result is 3x4
result = [[0,0,0,0],
[0,0,0,0],
[0,0,0,0]]
# iterate through rows of X
for i in range(len(X)):
# iterate through columns of Y
for j in range(len(Y[0])):
# iterate through rows of Y
for k in range(len(Y)):
result[i][j] += X[i][k] * Y[k][j]
for r in result:
print(r)
Matrix Multiplication Using Nested List Comprehension
# Program to multiply two matrices using list comprehension
# 3x3 matrix
X = [[12,7,3],
[4 ,5,6],
[7 ,8,9]]
# 3x4 matrix
Y = [[5,8,1,2],
[6,7,3,0],
[4,5,9,1]]
# result is 3x4
result = [[sum(a*b for a,b in zip(X_row,Y_col)) for Y_col in zip(*Y)] for X_row in X]
for r in result:
print(r)
50. Python Program to Access Index of a List Using for Loop¶
51. Python Program to Flatten a Nested List¶
my_list = [[1], [2, 3], [4, 5, 6, 7]]
flat_list = [num for sublist in my_list for num in sublist]
print(flat_list)
# Example 2: Using Nested for Loops (non pythonic way)
my_list = [[1], [2, 3], [4, 5, 6, 7]]
flat_list = []
for sublist in my_list:
for num in sublist:
flat_list.append(num)
print(flat_list)
# Example 3: Using itertools package
import itertools
my_list = [[1], [2, 3], [4, 5, 6, 7]]
flat_list = list(itertools.chain(*my_list))
print(flat_list)
# Example 4: Using sum()
my_list = [[1], [2, 3], [4, 5, 6, 7]]
flat_list = sum(my_list, [])
print(flat_list)
52. Python Program to Slice Lists¶
The format for list slicing is [start:stop:step].
55. Python Program to Check If a List is Empty¶
58. Python Program to Concatenate Two Lists¶
# Example 1: Using + operator
list_1 = [1, 'a']
list_2 = [3, 4, 5]
list_joined = list_1 + list_2
print(list_joined)
# Example 2: Using iterable unpacking operator *
list_1 = [1, 'a']
list_2 = range(2, 4)
list_joined = [*list_1, *list_2]
print(list_joined)
# Example 3: With unique values
list_1 = [1, 'a']
list_2 = [1, 2, 3]
list_joined = list(set(list_1 + list_2))
print(list_joined)
# Example 4: Using extend()
list_1 = [1, 'a']
list_2 = [1, 2, 3]
list_2.extend(list_1)
print(list_2)
60. Python Program to Split a List Into Evenly Sized Chunks¶
# Example 1: Using yield
def split(list_a, chunk_size):
for i in range(0, len(list_a), chunk_size):
yield list_a[i:i + chunk_size]
chunk_size = 2
my_list = [1,2,3,4,5,6,7,8,9]
print(list(split(my_list, chunk_size)))
[[1, 2], [3, 4], [5, 6], [7, 8], [9]]
chunk_size = 2
list_chunked = [my_list[i:i + chunk_size] for i in range(0, len(my_list), chunk_size)]
print(list_chunked)
# Example 2: Using numpy
import numpy as np
my_list = [1,2,3,4,5,6,7,8,9]
print(np.array_split(my_list, 5))
64. Python Program to Get the Last Element of the List¶
85. Python Program to Iterate Through Two Lists in Parallel¶
# Example 1: Using zip
list_1 = [1, 2, 3, 4]
list_2 = ['a', 'b', 'c']
for i, j in zip(list_1, list_2):
print(i, j)
95. Python Program to Remove Duplicate Element From a List¶
{1, 2, 12, 21, 34}
# Example 2: Remove the items that are duplicated in two lists
list_1 = [1, 2, 1, 4, 6]
list_2 = [7, 8, 2, 1]
print(list(set(list_1) ^ set(list_2)))
[4, 6, 7, 8]
[1, 21, 2, 12, 34]
l=[1,21,2,1,2,21,12,34]
l1= []
l1 = []
l3 = [l1.append(x) if x not in l1 else x for x in l]
print(l1)
l3
[1, 21, 2, 12, 34] [None, None, None, 1, 2, 21, None, None]