Python: For Loop

Sourabh Somani
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Introduction

In this article we will discuss about Python's for loop . Same like while loop, for loop also control flow statement. In Python, for loop is used when we want to iterate over a sequence.

Syntax:

for IterationalVariable in sequence:
Body of The loop

In Python, for loop works like C# foreach loop.

For loop with list

The following example explains how can you iterate list using for loop.

Example:

list=['C','C++','Java','C#']
print("This is our list ",list)
i=1
for val in list:
print("List Item",i,"is",val)
i=i+1

Output:

For loop with tuple

The following example explains how can you iterate tuple using for loop.

Example:

tuple=('C','C++','Java','C#','Python')
print("This is our Tuple ",tuple)
i=1
for val in tuple:
print("Tuple Item",i,"is",val)
i=i+1

Output:

For loop with string

The following example explains how can you iterate string using for loop.

Example:

string="C-Sharp Corner"
for val in string:
print(val)

Output:

Range Function

Sometimes we need to iterate loop in given range and we cannot create sequence. For example, if you want to print a number from one to 1000, so will you create a sequence or list from 1 to 1000? Of-course you cannot go like this. So in Python we have a range function, in which we will decide range inside the function.

Syntax of range function:

range([start],end,[step])

In Python range function has 3 arguments In which two are optional, which are the following:

start: This is an optional argument. This argument decides from where you want to start your loop. If you do not provide this value then its value will be zero(0) by default.
end: This argument decide the end of the loop.
step: How much you want to increment after one iteration. This is also an optional argument. So if you do not give this argument then it will increment by 1 step.

Example 1:

for val in range(11):
print(val)

In the above example range contains only one parameter so that it will be the end parameter and start and step will be set with its default value, so start will be 0 and step will be 1 and the value of end is 11.

Output:

Example 2:

for val in range(1,11):
print(val)

In the above example range contains two parameters so that it will be the start and end parameter and step will be set with its default value. So in the above example: start=1,end=11 and step=1(default).

Output:

Example 3:

for val in range(1,11,2):
print(val)

In the above example start=1 end=11 and step=2.

Output:

For loop with else condition

Same like while loop you can also use for loop with else condition in python. For loop works same like normal for loop but whenever for loop condition will be false its else part will execute.

Note: else part will only execute when for loop condition will be false. If for loop will be terminated by break statement then for loop's else part never executes.

Example:

#program to check
#weather the given number is
#prime number or not
num = int(input("Enter a Number : "))
for i in range(2,num):
if(num%i==0):
print("%d is not a prime number..."%num)
break
else:
print("%d is a prime number..."%num)

Output:

Nested Loop

Nested loop means loop inside loop. In python you can create loop inside loop.

Example 1:

str="";
for Row in range(0,7):
for Col in range(0,7):
if (((Col == 1 or Col == 5) and Row != 0) or ((Row == 0 or Row == 3) and (Col > 1 and Col < 5))):
str=str+"*"
else:
str=str+" "
str=str+"\n"
print(str);

Output:

Example 2:

str="";
for Row in range(0,7):
for Col in range(0,7):
if (Col == 1 or ((Row == 0 or Row == 3 or Row == 6) and (Col < 5 and Col > 1)) or (Col == 5 and (Row != 0 and Row != 3 and Row != 6))) :
str=str+"*"
else:
str=str+" "
str=str+"\n"
print(str);