Line comprehension is not functioning correctly in python

Question

I want to know why the code listed below is not functioning correctly.It should print 'Hi' but it is not printing it.Please look into this matter.Thanks in advance.

a=['{','}']
a=[(s.replace('{','H'),s.replace('}','i'))for s in a]
print(a)

You are replacing each element of the list with a tuple, not just updating an element — pink spikyhairman, May 03 '20 at 16:07
The code works correctly. If your real question is how to replace items in a list, that was already covered before multiple times, e.g. here: [finding and replacing elements in a list](https://stackoverflow.com/q/2582138/7851470). — Georgy, May 03 '20 at 16:42

score 3 · Answer 1 · answered May 03 '20 at 16:06

3

Use the following:

a=['{','}']
a=[(s.replace('{','H').replace('}','i'))for s in a]
print(a)

Output:

['H', 'i']

answered May 03 '20 at 16:06

Code Pope

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score 0 · Accepted Answer · answered May 03 '20 at 16:13

0

It is working properly. On the first element of the list, it encounters '{' which is computed to 'H' by s.replace('{','H') although '{' remains the same by applying s.replace('}','i') because the closing bracket ('}') is not encountered. Therefore, the result is ('H','{').

The same logic on the second element of the list.

answered May 03 '20 at 16:13

nprime496

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So why the '{' is printed.Using replace should not let it print – Ra143 May 03 '20 at 16:18
if the string to be replaced is not found, the initial string is returned. – nprime496 May 03 '20 at 16:22

score 0 · Answer 3 · answered May 03 '20 at 16:17

0

You are doing two operations, comma-separated in brackets, which produces two values, called a tuple (one result for each replace operation). Here's how to do what you want:

[s.replace('}','i').replace('{','H') for s in a]

answered May 03 '20 at 16:17

pink spikyhairman

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Bhargava V · Answer 4 · 2020-05-03T17:28:50.843

There are couple of things to being with. 1. You are trying to return a tuple and not a string, so 'Hi' is not possible. You would get '[('H', '{'), ('}', 'i')]'. 2. For string try below code. You should try replace on the list that is already replaced and then extract string out of it.

a=['{','}'] a=[s.replace('{', "H") for s in a] a=[s.replace('}',"i") for s in a] print("".join(a))

below is the single line code with same result.

a=['{','}'] print("".join([s.replace('{', "H").replace("}", "i") for s in a]))

Line comprehension is not functioning correctly in python

4 Answers4