Looping Statements are used to execute the set of statements
repeatedly. Python supports 2 types of looping statements –
1. for loop – for loop executes the set of
statements or blocks with respect to every element of the string/collection
objects. Syntax –
for variablename in string/collection variable :
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range() – range generates
the group of values based on the given range and gives it as a list.
Example –
print range(10) print range(1,11) print range(0,30,5) print range(0,10,3) print range(0,-10,-1) print range(0) print range(1,0)
Output –
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
[0, 5, 10, 15, 20, 25]
[0, 3, 6, 9]
[0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
[]
[]
In python for loop every time condition is not verified so performance will be
faster.
Example 1 –
for x in range(10): print x for y in range(0,10,2): print y for z in range(10): if z%2==0: print z
Output –
0
1
2
3
4
5
6
7
8
9
0
2
4
6
8
0
2
4
6
8
Example 2 –
x='rakesh' print x for p in x: print p,
Output –
rakesh
r a k e s h
2. while loop – while loop executes the set of statements or block repeatedly
until condition will become false. Syntax
while condition :
statement1
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Example 1 –
sum=0 spam=1 while spam<11: sum=sum+spam spam=spam+1 print sum
Output –
55
Example 2 –
name=' ' while name!='rakesh': name=raw_input('Enter name : ') print 'Thank you'
Output –
Enter name : barsha
Enter name : anjan
Enter name : bikash
Enter name : rakesh
Thank you
Example for infinite loop –
while True: name=raw_input('Enter name : ') print 'Thank you'
Output –
Enter name : barsha
Enter name : bikash
Enter name : anjan
Enter name : runjun
Enter name : rakesh
Enter name : apurba
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Break – break statements is used to exit from the loops. Generally, we use the
break statement in infinite loops.
Example –
while True: name=raw_input('Enter name : ') if name=='rakesh': break print 'Thank you'
Output –
Enter name : apurba
Enter name : barsha
Enter name : anjan
Enter name : bikash'
Enter name : rakesh
Thank you
Continue – continue statement can be used in the loops. Whenever we use
continue statement without executing the remaining part of the loop control
will goes to starting of the loop and continues the next iteration.
Example –
while True: name=raw_input('Enter name : ') if name!='rakesh': continue print 'hello rakesh, enter password' password=raw_input('Enter Password : ') if password=='hacker': break print 'Access granted'
Output –
Enter name : apurba
Enter name : rakesh
hello rakesh, enter password
Enter Password : hacker
Access granted
Example –
count=1 while True: if count==5: count=count+1 continue print 'hi ',count count = count+1 if count==10: break
Output –
hi 1
hi 2
hi 3
hi 4
hi 6
hi 7
hi 8
hi 9
Pass – Syntactically block is required but we don’t want to perform any action
logically then we can replace the block with ‘pass’. pass is a keyword it does
nothing.
Example –
i=100 while i<=100: pass if i<200: pass for i in range(10): pass
Del – del is a keyword, which is used to remove the variables or elements from
the memory location. After using the variables, then it is recommended to
remove those variables from the memory location by using ‘del’ keyword.
If you don’t remove the variables, after usage is over then those variables
available in the memory location until execution of the program is over, so that
performance of the application will be degraded. In garbage collector, it removes
spaces after entire program is completed but del is deleted within the program.
Example –
i=1000 j=2000 k=i+j print k del k x=i-j print x del x print k print x
Output –
3000
Traceback (most recent call last):
-1000
File "C:/Users/om/PycharmProjects/Pythonn/if3.py", line 9, in <module>
print k
NameError: name 'k' is not defined
Note – we can’t remove the elements of the immutable objects by using del
keyword but we can remove the immutable objects by using del keyword.
Example –
i='rakesh' del i x='apurba' del x[2]
Output –
Traceback (most recent call last):
File "C:/Users/om/PycharmProjects/Pythonn/if3.py", line 4, in <module>
del x[2]
TypeError: 'str' object doesn't support item deletion
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