Control
Structure in Python
Looping
/ Iterative Statements in Python
What is Loop?
In any programming language loop is a statement used
to execute a certain block of code repeatedly until certain condition met. A statement or group of statements are
executed repeatedly until condition satisfy. Once condition becomes false loop
iteration will stop.
In Python there are two types of loops
1.
for
Loop:
Normally for loop is used to iterate the elements in the
sequence in Python.
Syntax,
for
variable in sequence:
statement to be executed repeatedly
for keyword is used to write the for loop. Variable is
the name of variable used for loop iteration. In keyword is used to check each
element from given sequence i.e. in list, in tuple, in set, in dictionary. Sequence
is the name of sequence.
For example,
my_list=["book1","book2","book3",1,2,3]
for element in my_list:
print(element)
Output:
book1
book2
book3
1
2
3
In above program list is created with some random
elements. For Loop is applied ove the list my_list. Element is loop variable to
iterate loop until condition satisfy.
For Loop with range Method:
For loop is used with range method to give particular
range to loop variable.
Syntax:
for variable in range(start,stop,step):
statement
to execute
Here for keyword is used to write for loop in keyword
is used to give the range for the iteration. In range() function three
parameters are passed start to start your loop from a particular value, end is
nothing but to terminate the loop and step is nothing but after each iteration
loop will be incremented or decremented by which value is given. This is
followed by the colon. After colon the body of the loop has to followed by indentation.
By default, 4 spaces are given before starting the loop statement.
For example,
sum=0
for
i in range(1,11,1):
sum=sum+i
print("The
sum of first 20 natural numbers is:",sum)
Output:
The
sum of first 20 natural numbers is: 55
Above program is written to perform sum of first 10
numbers. By using range function three parameters are passed i.e. loop will
start from 1 it is start value. Loop will end on 11. So total 1 to 10 numbers
will be taken for sum. Third value is again 1 i.e. step value. After each iteration
loop variable, I will be incremented by 1. In this way we can use for loop to
perform sum of natural numbers using range function
2. The
while Loop:
The while loop is used to execute statement or group of statements repeatedly
but you don’t know initially how many iterations will be there. In advance if
you don’t know how many iterations are there.
General syntax:
while variable testcondition:
statement
to execute
while keyword is used to write while loop. Variable is name of loop
variable to iterate. Test condition is written to iterate the loop up to that
number. Colon is part of syntax and then the while loop statement is written
after following indentation. The loop
statement is executed repeatedly until test condition is true. Once condition
becomes false loop iteration will stop.
For example,
i=1
while i<=10:
print(i)
i+=1
Output:
1
2
3
4
5
6
7
8
9
10
In above program the while loop is written to print first 10 natural numbers. The I variable is initialized with 1. In while loop test
condition is written i<=10 means loop the statement written in while loop
print(i) will be executed repeatedly until condition satisfy. Once compiler
will get 11 loop iteration will stop. After each iteration loop will be
incremented by 1.
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