Page 227 - Computer Science Class 11 Without Functions
P. 227
9.8 Infinite Loop
A while loop becomes an infinite loop if the test condition never yields False. For example,
01 while True:
02 s = 1
03 print(s)
In the above code snippet, the test expression always yields True. But you may ask, why would anybody write a code
like the one above. Of course, no one would, except by an error. Next, consider the following code snippet. The code
aims to find the sum of positive numbers entered by a user. The control leaves the loop as soon as it encounters zero
or a negative number, and the sum of the positive numbers is printed.
01 sumNums = 0
02 num = int(input('enter a number: '))
03 while num>0:
04 sumNums = sumNums + num
05 num = int(input('enter a number: '))
06 print('Sum of all numbers: ', sumNums)
In the above code, we are required to include the code to input a number twice, whereas it is indeed part of the loop.
So, the following code that sets the Boolean expression in the while loop as True would be better:
01 sumNums = 0
02 while True:
03 num = int(input('enter a number: '))
04 if num>0:
05 sumNums = sumNums + num
06 else:
07 break
08 print('Sum of all numbers: ', sumNums)
9.9 pass Statement
A pass statement is ignored by the Python interpreter. It has the following simple syntax:
pass
It is often used as a stub when we want to leave some functionality to be defined in the future. For example, pass
statement can be used when no action is required on some conditions. For example,
01 for letter in 'world':
02 if letter == 'l':
03 pass
04 else:
05 print(letter, end='')
Sample Output:
word
It is important to remember that only the pass statement is ignored, other statements if any in the block are not
ignored. For example,
01 for letter in 'world':
02 if letter == 'l':
03 pass
04 print(letter, end ='')
05 else:
06 print(letter, end='')
Sample Output:
world
Looping in Python 225

