Difference between revisions of "Python-3.4.3/C3/Loops/English"

Objectives

• for loop
• while loop
• break, continue and pass statements in the loops

System Specifications

• Ubuntu Linux 16.04 operating system
• Python 3.4.3 and
• IPython 5.1.0

Pre-requisite

• use conditional statements

If not, see the relevant Python tutorials on this website.

while loop

Syntax:

while <condition>:

#True block statements

#update condition variable

#statements after while loop

The while loop is used to execute a set of statements as long as a condition is true.

When the condition becomes false, program control passes to the line immediately after the loop.

The code inside the while loop should be indented four spaces to the right.

Open the terminal.

Press Enter

From here onwards, remember to press the Enter key after typing every command on the terminal.

i = 1

while i<10:

print (i*i)

i += 2

Type,

i is equal to 1

while i less than 10 colon

print inside brackets i asterisk i

i plus equal to 2

Highlight

print (i*i)

i += 2

If it is True, it executes the block of code within the loop.

Then press the Enter key twice to get the output.

<<PAUSE>>

for n in range(1, 10, 2):

print (n*n)

Highlight for

Highlight range

Type,

for n in range inside brackets 1, 10, 2 colon

print inside brackets n asterisk n

As we know, the for loop iterates over a list or any other sequential data type.

So, we use the range function to get a list of odd numbers below 10 and iterate over it.

Then we print the square of n.

Highlight both the outputs

We can see that we got the same output as before.

Note that now the lines of code are less.

Try this exercise and then resume the video.

while i<10:

print (i*i)

i += 2

Enter twice

Highlight the output

while i less than 10 colon

print inside brackets i asterisk i

i plus equal to 2

Press the Enter key twice.

We got the required output.

Try this exercise and then resume the video.

Assignment 2

print (n*n)

Enter twice

Highlight the output

for n in range inside brackets 2, 10, 2 colon

print inside brackets n asterisk n

Press Enter twice.

We got the required output.

<<PAUSE>>

for n in range(2, 10, 2):

pass

Highlight pass

Enter twice

Now type this code to understand the pass statement.

As we already know, pass is just a placeholder.

It is used for the sake of completion of blocks, that do not have any code within them.

Nothing gets printed when we execute this code.

Press Enter twice.

As we expected nothing gets printed.

for letter in 'python':

if letter == 'h':

break

print ('Current Letter :', letter)

Highlight break

Enter twice

break is used to break the innermost loop.

Type the code as shown.

Here, it will iterate each letter in the word python.

And it breaks the loop when h is the iteration value.

Press Enter twice to see the output.

if n % 3 == 0:

continue

print (n*n)

Press Enter twice

Out

Type the code as shown.

The continue statement rejects all the remaining statements in the current iteration of the loop.

And it moves the control back to the top of the loop.

It will print the squares of all the odd numbers below 10 which are not multiples of 3.

Press Enter twice.

We got the required output.

Summary

Let us summarise.

In this tutorial, we have learnt to,

• Iterate over a sequence using for and while loops
• Break out of loops using break statement
• Skip iterations using continue statement
• Use the pass statement in a loop

Evaluation

1. Given range(1,4), write a code to print only the number 1.
2. Which statement do you use to skip iterations?

Solution of self assessment questions

1. We can use the break statement in the for loop as shown here

1. In order to skip iterations, we can use the continue statement.

Acknowledgment

For more details, visit this website.