This document contains summaries of two lectures on updating variables and iteration in Python programming. Lecture 17 discusses reassignment of variables to new values and updating variable values based on their previous values. Lecture 18 introduces for and while loops for automating repetitive tasks, the break keyword to terminate loops, and calculating square roots through iterative approximation. The document provides examples of reassigning variable values, updating variables, using for and while loops, and computing square roots with the iterative formula.

1. Python Programming
Unit – III (Part I)
(Lecture 17)
Updating variables
& Iteration

2. Python Programming
Unit – III (Part I)
(Lecture 17)
Updating variables & Iteration
Reassignment Updating variables

3. Updating variables & Iteration
Lecture 17
Lecture 18
Reassignment
Updating variables Break
Square roots
for & while statement

4. Lecture 17
Reassignment
Updating variables
Updating variables

5. • More than one assignment
to the same variable.
• A new assignment makes
an existing variable refer to
a new value (and stop
referring to the old value)
Reassignment
a = 5
Print (a) is 5
a = 6
Print (a) is 6

6. Lecture 17
Reassignment
Updating variables
Updating variables

7. Updating variables
• The new value of the
variable depends on
the old.
x = x + 1
• Get the current value
of x, add one, and then
update x with the new
value.
• Before you can update a
variable, you have to
initialize it, usually with
a simple assignment:
x = 5
x = x+1

8. Lecture 17
Reassignment
Updating variables
Updating variables

9. Python Programming
Unit – III (Part I)
(Lecture 18)
Updating variables
& Iteration

10. for & while statement
Python Programming
Unit – III (Part I)
(Lecture 18)
Updating variables & Iteration
Break Square roots

11. Lecture 17
Lecture 18
Reassignment
Updating variables Break
Square roots
for & while statement
Updating variables & Iteration

12. Iteration
Lecture 18
Break
Square roots
for & while statement

13. for & while statement
• Computers are often
used to automate
repetitive tasks.
• Repeating identical or
similar tasks without
making errors
• Two main loop
statements are
available.
for
while

14. Iteration
Lecture 18
Break
Square roots
for & while statement

15. Break
• The break is a keyword in
python which is used to
terminate the loop.
• It breaks the inner loop first
and then proceeds to outer
loops.
while True:
line = input('Enter line to print: ')
if line == 'Exit':
break
print (line)

16. Iteration
Lecture 18
Break
Square roots
for & while statement

17. Square roots
• Suppose that you want to know
the square root of a.
• Take x initially, compute a better
estimate with the following
formula:

18. Square roots

19. Square roots

20. Iteration
Lecture 18
Break
Square roots
for & while statement