Python For Loop how to use Examples

Python, python-loops

in this post, we are going to understand Python For Loop how to use Examples that include how to use for loop to iterate over a List, a tuple, a dictionary and for loop range(), for loop with else, for loop with continue statement.

What is the need of loops?

  • Loops in any programming language are used to execute the same set of statements n numbers of times.
  • Suppose we have to print the names of 100 employees instead of writing 100 print statements. We can run a loop that executes the same code statement 100 times.

How to use Python for loop

For Loop in Python is used to iterate over a sequence ( list, string, tuple), iterables(set, dictionary), numeric range sequence, and run some blocks of code till the size of the sequence, numeric range sequence, or iterable meets the condition set for this loop.

iteration: The action of looping over the sequence or iterable is known as iteration

Syntax of for loop in python

for variable in sequence
   ...code statement_1
    ...code statement_2
    ...code statement_N
  • Variable: In this syntax, the variable represents each element of sequence or iterable, the value of variable changes on each iteration it takes values of the next item.
  • Sequence :This represent sequence (list,string,tuple) or iterable(dictionary,set)

Note: In python, We separate the code body of the loop by using indention.

1. Python for loop a tuple

In this code, the item is a variable and num_tuple is a sequence, and print(item) is the code block of for loop that is repeating each element of tuple till the last element of the tuple.

num_tuple = ('A','BC','CD','EF')

print('iterate over each element of a tuple:')

for item in num_tuple:  
  print(item)

Output

iterate over each element of a tuple:
A
BC
CD
EF

2. Python for loop a Dictionary

Here, We are iterating over iterable num_dict dictionary’s key-values pairs using for loop.

num_dict = {'A':65,'BC':67,'CD':68,'EF':69}

print('iterate over each key-value pair of a dictionary:')

for item in num_dict.items() :  

  print(item[0] ,':',item[1])

Output

iterate over each element of a dictionary:
A : 65
BC : 67
CD : 68
EF : 69

3. Python for loop a list or array

Here we are looping the sequence (my_list) using for loop.

my_list= ['A','EF',69]

print('using for loop iterating over each item of a list:')

for item in my_list :  

  print(item)

Output

using for loop iterating over each items of a list:
A
EF
69

4. Python for loop Range()

Unlike other programming languages, Python does not have an in-built numeric loop. So this can be achieved by using Python’s built-in range() function.

Numeric for Loop in C#,Java,C++ 

for(int i=0;i<5;i++)

The range() function comes in handy, whenever we have to run a for loop for numeric sequence. It can create a sequence of numbers, For example, pass 5 as an argument to range(5), it generates numbers from 0 to 4.

Syntax

range(start,stop,step)
  • Start: start index of number sequence, by default it is 0.
  • End: End index of a numeric sequence, default is the end of the sequence.
  • Step: It represents how many numbers to skip on each iteration by default is 1, it raises ValueError if it is 0.

Example: For loop with range() function

It is a simple example of loop iteration over the sequence 0 to 4.

print('iterate over a sequence of number:')

for item in range(5):  
  print(item)

Output

iterate over a sequence of number:
0
1
2
3
4

Example:For Loop range(start,stop,end)

Here, we have to specify the start, end, step parameter values of range() function, we want to start from index 2 and end on index 10, the number of sequences we are skipping is 2 on each item iteration. It is kind of a step size of 2.

print('iterate sequnce of number with start,stop,end parameter:')

for item in range(2,10,2):  
  print(item)

Output

iterate sequence of number with start, stop, end parameter:
2
4
6
8

5. Python For loop else block

The use of optional else-block with for loop adds more advantage to the python for -loop as compared to other languages. If we need to execute some code after the for-loop terminated then we can use else block with Python for the loop.

For loop with else block

num_list = [2,1,13]

mutiply = 1;
for item in num_list :
        if item != 0:
         mutiply = mutiply * item
        print('mutiplication  :',mutiply)
else:       
        print('loop terminated')

Output

mutiplication  : 2
mutiplication  : 2
mutiplication  : 26
loop terminated

The for…..else block can also be used with a break statement. In this case, if the break terminates the loop, then else block will not execute.

def finditem(num_list):

 item ='A'
 for item in num_list :
        if item  == 'A':         
          print('Item found:',item)
          break
 else:       
        print('no item found:')

#used finditem function
finditem( num_list = ['B','C','A'])

Output

Item found: A

6. Python For loop continue statement

Python also supports continue statements with for loop like other programming languages. If you want to continue the loop, even the condition is true.

num_list = [0,12,0,6,0,3]
mutiply = 1;
 
for item in num_list :
        if item ==0:
          continue  
        mutiply = mutiply*item       
          
   
print('multiplication of non-zero items : ',mutiply)

Output

multiplication of non-zero items :  216

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