To manage looping requirements,
the Python programming language supports the following types of loops. The
loops can be executed in three different ways in Python. While all of the
methods provide comparable fundamental functionality, they differ in syntax and
the time it takes to check for conditions.
While
Loop:
While loops are used in Python
to run a block of statements repeatedly until a condition is met. When the
condition in the programme turns false, the line immediately following the loop
is performed.
Syntax
|
while expression: statement(s) |
After a programming construct,
any statements indented by the same number of character spaces are regarded to
be part of a single block of code. Python's way of grouping statements is
indentation.
|
#Write a Program to illustrate while loop in Python count = 0 while (count < 3): count
= count + 1 print("www.a2pstudy.com") |
|
Output: |
While
Loop Using else Statement
As explained previously, the
while loop performs the block until a condition is met. The statement
immediately following the loop is performed when the condition turns false.
When your while condition is
false, the else clause is performed. It will not be run if you exit the loop or
if an exception is triggered.
Syntax
|
while condition: #
execute these statements else: #
execute these statements |
Example:
|
#Write a Program to illustrate combining else with while
in Python count = 0 while (count < 3): count
= count + 1 print("www.a2pstudy.com") else: print("Else
Block Executed") |
|
Output: Else Block Executed |
For
Loop in Python
For sequential traversal, loops
are utilized. For instance, traversing a list, string, or array There is no C
style for looping in Python, i.e. for (i=0; in; i++). There is a "for
in" loop, which is analogous to other languages' for each loop. Let's have
a look at how to utilise the for in loop to do sequential traversals.
Syntax
|
for var in sequence: statements(s) |
On each iteration, var is the
variable that takes the value of the item inside the sequence.
The loop will continue until
the last item in the sequence is reached. Indentation is used to separate the
body of the for loop from the remainder of the code.
|
# Program to find the sum of all numbers stored in a list # List of numbers numbers = [6, 5, 3, 8, 4, 2, 5, 4, 11] # variable to store the sum sum = 0 # iterate over the list for val in numbers: sum
= sum+val print("The sum is", sum) |
|
Output: The sum is 48 |
The
range() function
The range() method can be used
to create a numeric series. range(10) generates a range of values from 0 to 9.
(10 numbers).
Range(start,
stop, step size) may also be used to define the start, stop, and
step size. If step size is not specified, it defaults to 1.
|
# Write a Python Program to illustrate Iterating over range 0 to n-1 n = 4 for i in range(0, n): print(i) |
|
Output: 0 1 2 3 |
|
# Write a Python Program to illustrate Iterating over a list print("List Iteration") l = ["www.a2pstudy.com",
"for", "www.a2pstudy.com"] for i in l: print(i) # Iterating over a tuple (immutable) print("\nTuple Iteration") t = ("www.a2pstudy.com",
"for", "www.a2pstudy.com") for i in t: print(i) # Iterating over a String print("\nString Iteration") s = " a2pstudy" for i in s : print(i) # Iterating over dictionary print("\nDictionary Iteration") d = dict() d['xyz'] = 123 d['abc'] = 345 for i in d : print("%s
%d" %(i, d[i])) |
|
Output: List Iteration www.a2pstudy.com for www.a2pstudy.com Tuple Iteration www.a2pstudy.com for www.a2pstudy.com String Iteration a 2 p s t u d y Dictionary Iteration xyz 123 abc 345 |
Iterating
by index of sequences
It is also possible to iterate
using the sequence's index. The fundamental concept is to compute the list's
length first, then loop over the sequence within that range.
|
# Write a Python Program to illustrate Iterating by index list = ["Study", "with",
"a2pstudy"] for index in range(len(list)): print
list[index] |
|
Output: Study with a2pstudy |
For
loop with else Statement
Like with a while loop, we may
combine an else statement with a for loop. However, because there is no
condition in the for loop that will cause the execution to end, the otherwise
block will be run immediately after the for block.
|
# Write a Python Program to illustrate Iterating by index with else block list = ["Study", "with",
"a2pstudy"] for index in range(len(list)): print
list[index] else:
print(“This is else Block”) |
|
Output: Study with a2pstudy This is else Block |
Nested
Loop in Python
The Python programming language
allows you to nest loops inside loops. A few examples are provided in the next
section to demonstrate the idea.
Nested
for Loop
Syntax
|
for var in sequence: for var
in sequence: statements(s) statements(s) |
Nested
while Loop
The syntax for a nested while
loop statement in Python programming language is as follows:
Syntax
|
while expression: while
expression: statement(s) statement(s) |
Example:
|
# Write a Program to illustrate nested for loops in
Python for i in range(1, 5): for
j in range(j): print(i,
end=' ') print() |
|
Output: 1 1 2 1 2 3 1 2 3 4 |
At last, we can say that we can
use the loop inside a same or different type of loop. Like while inside for or
for inside while and vice-versa.
