Python: In loop variable used within a statement not updated

Question

I am trying to write a piece of code that takes a string as input and replaces * for a range of numbers, sort of like:

I am * years old

0-10

I am 0 years old

I am 1 years old

...

This is an attempt to make my life easier on R while I also learn some Python. Here is my code:

yourtext = input(" ")
number = input(" ")
number = int(number)

while number > 0:
    i = str(number)
    print(i)
    yourtext = yourtext.replace("*", i)
    print(yourtext)
    print(number)
    number = number - 1

And right now, this returns:

*
5 (my inputs)

5
5
5
4
5
4
3
5
3
2
5
2
1
5
1

So it seems like the i inside the replace function is fixed at its value on the first iteration of the loop. Why is this and how can I change it? Thanks a lot for your help.

Can you make sure your indents are placed correctly for each line? Python is indent sensitive — Capn Jack
– Capn Jack, Commented Oct 9, 2018 at 21:30

Håken Lid · Accepted Answer · 2018-10-09 21:33:46Z

1

After you replace * with a number, the next iterations of the loop will do nothing. There are no more * in yourtext.

yourtext = yourtext.replace("*", i)

answered Oct 9, 2018 at 21:33

Håken Lid

23.2k10 gold badges58 silver badges73 bronze badges

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

Comments

C.Nivs · Accepted Answer · 2018-10-09 21:37:17Z

0

I'd ditch the while loop in favor of for, since you could get caught in an infinite loop that way. Also, for will take a range of values so you don't have to manually increment your value:

yourtext = input("What would you like? ")
number = int(input("What is the number? ")

if '*' not in yourtext:
    raise ValueError("could not find wildcard")

for i in range(number):
    print(yourtext.replace("*", i)

answered Oct 9, 2018 at 21:37

C.Nivs

13.2k3 gold badges21 silver badges48 bronze badges

Comments

skelley · Accepted Answer · 2018-10-09 21:40:33Z

You're really close! Your only problem here is that the line:

yourtext = yourtext.replace("*", i)

is updating the yourtext variable. So after your first iteration through the loop, you've changed the "*" in yourtext to be the number. So instead of yourtext being the string "I am * years old" (in your original example) it gets changed to "I am 5 years old". Then, when you go through the loop again, there is no "*" to replace (because the string "I am 5 years old" has no *), so the text stays as "I am 5 years old" instead of changing to "I am 4 years old".

You can fix that by making a new temporary variable instead, for example replacing the problem line with:

updated_text = yourtext.replace("*", i)

SkylerF · Accepted Answer · 2018-10-09 21:40:46Z

0

Not sure what the purpose of yourtext is, but after you replace the "*" the first time, yourtext will not update since it doesn't contain a * anymore. For example, if you input "test" instead of *, yourtext will never update because there is no * in the first place

4
test
4
3
test
3
2
test
2
1
test
1

answered Oct 9, 2018 at 21:40

SkylerF

607 bronze badges

Comments

vash_the_stampede · Accepted Answer · 2018-10-09 21:58:57Z

0

You could do this in a loop with string.replace()

s = 'I am * years old'
number = 10

for i in range(number +1):
    print('{}'.format(s.replace('*', str(i))))

I am 0 years old
I am 1 years old
I am 2 years old
I am 3 years old
I am 4 years old
I am 5 years old
I am 6 years old
I am 7 years old
I am 8 years old
I am 9 years old
I am 10 years old

answered Oct 9, 2018 at 21:58

vash_the_stampede

4,5861 gold badge11 silver badges20 bronze badges

Collectives™ on Stack Overflow

Python: In loop variable used within a statement not updated

5 Answers 5

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related