How to replace multiple (non-unique) substrings in a string?

Question

I have this string -

test_str = 'hello_2Testsmthhello_1smthhello_1'

and I have a list of strings -

list1 = ['hello_1', 'hello_2']

Now I want to replace hello_1 and hello_2 with a period(.). This is what I've tried -

for i in list1:
    h = test_str.replace(str(i), ".")
#print (h)

This gives me the string - .Testsmthhello_1smthhello_1

However, the expected output is - .Testsmth.smth.

Can anyone help me here?

Where you have written h = test_str.replace(str(i), "."), do you expect this to change the value of test_str? Why or why not? If it doesn't change, then can you explain how you expect the loop to work? — Karl Knechtel
– Karl Knechtel, Commented Mar 22, 2021 at 5:37
In general, you should try to think about your code first, and step through the logic of it. Please read ericlippert.com/2014/03/05/how-to-debug-small-programs . — Karl Knechtel
– Karl Knechtel, Commented Mar 22, 2021 at 5:38
Okay, so the first time through the loop, you do h = test_str.replace(str(i), "."), so h ends up with the result of doing the first replacement, and test_str is the same as before. Right? So, what do you think will happen the second time through the loop, given that test_str didn't change? Again: try to think about your code first, and step through the logic of it. — Karl Knechtel
– Karl Knechtel, Commented Mar 22, 2021 at 5:43
@KarlKnechtel - Thanks for your advice.. I didn't think of it that way.. — NST
– NST, Commented Mar 22, 2021 at 5:46

Ash W · Accepted Answer · 2021-03-22 05:47:24Z

1

You can simply change the h in the loop to test_str :)

for i in list1:
    test_str = test_str.replace(str(i), ".")

In your original loop, you did successfully replace the substrings with . in test_str but you didn't save this change. test_str stayed the same and h got a brand new value in each loop. As you can see by printing the values during the loop.

for i in list1:
    print(i)
    h = test_str.replace(str(i), ".")
    print(h)
    print(test_str)

Hopefully I explained this clearly.

answered Mar 22, 2021 at 5:47

Ash W

305 bronze badges

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

Comments

Krishna Chaurasia · Accepted Answer · 2021-03-22 05:36:14Z

0

replace() returns a copy of the string with the replaced version so you need to assign it back to test_str:

test_str = 'hello_2Testsmthhello_1smthhello_1'
list1 = ['hello_1', 'hello_2']
for i in list1:
    test_str = test_str.replace(i, ".")
    
print(test_str) #.Testsmth.smth.

answered Mar 22, 2021 at 5:36

Krishna Chaurasia

9,6546 gold badges27 silver badges44 bronze badges

Comments

Gilseung Ahn · Accepted Answer · 2021-03-22 05:36:52Z

0

It is because test_str is replaced only once. Do not use h for your intent.

for i in list1:
    test_str = test_str.replace(str(i), ".")

If you do not want to change test_str, then make a copy as follows.

import copy
h = copy.copy(test_str)

for i in list1:
    h = h.replace(str(i), ".")

answered Mar 22, 2021 at 5:36

Gilseung Ahn

2,6421 gold badge6 silver badges14 bronze badges

Comments

Sociopath · Accepted Answer · 2021-03-22 05:39:44Z

0

You can use regex for it

import re

test_str = 'hello_2Testsmthhello_1smthhello_1'

pattern = r'hello_\d'

print(re.sub(pattern,'.', test_str))

answered Mar 22, 2021 at 5:39

Sociopath

13.4k22 gold badges53 silver badges82 bronze badges

Collectives™ on Stack Overflow

How to replace multiple (non-unique) substrings in a string?

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related