Loops and Conditions

‘while’ loop

Let us demonstrate the ‘while’ loop by writing the multiplication table for 9 in both PERL and Python.

The PERL code -

$i=1;
while($i<=10)
{
       print 9*$i, “\n”;
       $i++;
}
 

Python code -

i=1
while(i<=10):
       print 9*i
       i=i+1

Apart from the differences mentioned in chapter 2, two codes are identical.

‘if-else’

PERL code -

$i=15;
if($i>10) {
       print “$i greater than 10\n”;
}
else {
       print “$i less than 10\n”;
}

Python code -

i=15
if(i>10):
       print “$i greater than 10\n”;
else:
       print “$i less than 10\n”;

‘for’ Loops

PERL code -

for($i=1; $i<11; $i++)
{
    print “5 times”, $i, “is”, 5*$i, “\n”;

}
print “completed for loop”

Python code -

for i in range(1,11):
      print “5 times”, i, “is”, 5*i

print “completed for loop”

Using ‘for’ over a Dictionary

age={}
age['john']=12
age['paul']=77

for key in age:
        print key
        print age[key]+7

When ‘for’ is written on a dictionary, the loop variable takes the values of
the keys of the dictionary.

Keywords ‘break’ and ‘continue’

‘While’ loops become even more powerful, when they are customized using an
internal condition (‘if’). The keywords ‘break’ and ‘continue’ come handy in that situation.

i=0
while True:
    i=i+1
    if i==4:
        break
    print “5 times”, i, “is”, 5*i

In the above code, the condition for ‘while’ is always True. Therefore, it is expected to run infinite times. That does not happen, because the loop is terminated using ‘break’, when i reaches 4.

i=0
while i<10:
    i=i+1
    if i==4:
        continue
    print “5 times”, i, “is”, 5*i

The keyword ‘continue’ skips over the remaining lines of the ‘while’ block and starts the following run of the ‘while’ loop.