Python For Loop Statement

Python Loops

A loop statement allows us to execute a statement or group of statements multiple times.

Python has two primitive loop commands:

  • while loops
  • for loops

  • For Loop

  • The for loop in Python is used to iterate over a sequence (list, tuple, string) or other iterable objects.
  • Iterating over a sequence is called traversal.


  • Syntax:

    for iterating_var in sequence:
        statements(s)
    
  • The first item in the sequence is assigned to the iterating variable iterating_var.
  • Next, the statements block is executed.
  • Each item in the list is assigned to iterating_var, and the statement(s) block is executed until the entire sequence is exhausted.
  • # Program to print the fruits available inside the list
    fruits = ["Apple", "Banana", "Cherry","Mango","Pineapple","Jackfruit"]
    
    for x in fruits:
        print(x)
        
    Output:
    Apple
    Banana
    Cherry
    Mango
    Pineapple
    Jackfruit
    
    # Program to print the numbers available inside the list
    numbers = [0, 1, 5, 10, 15, 45, 50]
    
    for i in numbers:
        print(i)
        
    Output:
    0
    1
    5
    10
    15
    45
    50
    

    Using else Statement with Loops

    If the else statement is used with a for loop, the else statement is executed when the loop has exhausted iterating the list.

    # Program to print the numbers available inside the list using else statement
    numbers = [0, 1, 5, 10, 15, 45, 50]
    
    for i in numbers:
        print(i)
    else:
        print("No items left")
        
    Output:
    0
    1
    5
    10
    15
    45
    50
    No items left
    
    # Program to find the sum of all numbers stored in a list
    
    # List of numbers
    numbers = [0, 1, 5, 10, 15, 45, 50]
    
    # variable to store the sum
    sum = 0
    
    # iterate over the list
    for val in numbers:
        sum = sum + val
    
    print("The sum of numbers in the list is", sum)
    
    Output: 
    The sum of numbers in the list is 126
    

    Looping Through a String

    # Program to print each character of a string
    for x in "banana":
        print(x)
        
    Output:
    b
    a
    n
    a
    n
    a
    

    The range() function

  • We can generate a sequence of numbers using range() function.
  • We can also define the start, stop and step size as range(start,stop,step size). step size defaults to 1 if not provided.
  • This function does not store all the values in memory, it would be inefficient. So it remembers the start, stop, step size and generates the next number on the go.
  • # Program to generate 10 numbers starting from 0 to 9 using Range Function
    print(range(10))
    
    Output:
    range(0, 10)
    
    # Program to display the numbers using Range Function
    for x in range(10):
        print(x)
    
    Output:
    0
    1
    2
    3
    4
    5
    6
    7
    8
    9
    
    # Program to display the numbers between 2 values using Range Function 
    for x in range(2,6):
        print(x)
    
    Output:
    2
    3
    4
    5
    
    # Program to display the numbers between 2 values using step size
    for x in range(1, 30, 2):
        print(x)
    
    Output:
    1
    3
    5
    7
    9
    11
    13
    15
    17
    19
    21
    23
    25
    27
    29
    

    Iterating by Sequence Index

    An alternative way of iterating through each item is by index offset into the sequence itself.

    # Program to iterate through a list using indexing
    fruits = ["Apple", "Banana", "Cherry","Mango","Pineapple","Jackfruit"]
    
    for index in range(len(fruits)):
        print ('Fruit name is :', fruits[index])
    
    Output:
    Fruit name is : Apple
    Fruit name is : Banana
    Fruit name is : Cherry
    Fruit name is : Mango
    Fruit name is : Pineapple
    Fruit name is : Jackfruit
    
    # A list of fruits
    fruits = ["Apple", "Banana", "Cherry","Mango","Pineapple","Jackfruit"]
    
    ## Read fruits list and enumerate into index and value
    # Enumerate() method adds a counter to an iterable and 
    
    returns it in a form of enumerate object. for index,value in enumerate(fruits): print(index,value) # print ('Fruit Index is',index,'and Fruit name is :',value) Output: 0 Apple 1 Banana 2 Cherry 3 Mango 4 Pineapple 5 Jackfruit

    Nested For Loop

    Python programming language allows to use one for loop inside another for loop.

    # Nested for loop example 
    for x in range(1,4):  # 1 ,2, 3
        ### Inner for loop	 ###
        for y in range(1,4):
            print(x,y)
    
    Output:
    1 1
    1 2
    1 3
    2 1
    2 2
    2 3
    3 1
    3 2
    3 3
    
    # Nested for loop example
    adj = ["red", "big", "tasty"]
    fruits = ["apple", "mango", "banana"]
    
    for x in adj:
        for y in fruits:
            print(x, y) 
    
    Output:
    red apple
    red mango
    red banana
    big apple
    big mango
    big banana
    tasty apple
    tasty mango
    tasty banana
    
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