Using a nested for loop in python to print a rectangle

Question

I saw my same question asked but I want to know why what I'm trying isn't working. This is from a Zybook challenge question.

Here is the exercise:

Write nested loops to print a rectangle. Sample output for given program:

* * *  
* * *

This is the code I built:

num_rows = 2
num_cols = 3

for num_rows in range(0,num_rows):
    for num_cols in range(0,num_cols):
        print('*', end=' ')
    print('')

The output is:

* * *
* *

Question: Why doesn't the nested for loop print statement iterate for the third time? When I set the nested loop to:

for num_cols in range(0,3):

I receive my desired output of the 3x2 asterisk rectangle. If the num_cols variable is declared as 3, shouldn't the output statement equal my desired output?

Because you are using the same identifier num_rows and num_cols for the previously befined variables and the ones used in the for loop. Rename the latest ones to something like row and col instead of num_rows and num_cols. — dabadaba
– dabadaba, Commented Oct 21, 2017 at 14:51
That's it, thank you. I was scouring my books and I didn't realize that was the error I was making. — David Scott II
– David Scott II, Commented Oct 21, 2017 at 14:56
Basically you were overwriting the original num_rows and num_cols in the loop. — dabadaba
– dabadaba, Commented Oct 21, 2017 at 15:00

Karthik · Accepted Answer · 2017-10-21 16:46:56Z

1

You are overwriting the num_cols variable by using it as the looping variable as well as the number of columns value. It gets set to 2 during the end of the first iteration of the outer loop. You can replace it with num_col. Same applies for num_rows as well

answered Oct 21, 2017 at 16:46

Karthik

364 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

BoltzmannBrain · Accepted Answer · 2017-10-21 16:58:26Z

0

Following up @Karthik's reasoning of why your code is incorrect, here's a solution with misc. improvements:

num_rows = 2
num_cols = 3

for _ in xrange(num_rows):       # xrange for efficient iteration
    for _ in xrange(num_cols):   # no need to unpack iteration variable
        print '*',               # for Python 2, but use the function syntax for 3+
    print ''

answered Oct 21, 2017 at 16:58

BoltzmannBrain

5,49213 gold badges55 silver badges83 bronze badges

Collectives™ on Stack Overflow

Using a nested for loop in python to print a rectangle

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related