Adding Characters to an Empty String in Python

Question

I am attempting to have my program iterate over a user-inputted string and print it again, with a "u" in place of every uppercase letter, an "l" in place of every lowercase letter, and a "-" in place of any other character. This is what I have written:

txt = input()
modified_txt = ""

for char in txt:
    if char.isupper():
        modified_txt + "u"
    elif char.islower():
        modified_txt + "l"
    else:
        modified_txt + "-"

print(modified_txt)

For some reason, my output is a blank line, as though the variable "modified_txt" was never affected by the for loop. I'm sure there's a straightforward reason why this is the case but I'm at a loss.

strings are immutable, meaning you can't modify them like this, you can tho use += to reassign and add a character, so modified_txt += "u" and so on (it's equivalent to modified_txt = modified_txt + "u") — Matiiss
– Matiiss, Commented Jul 20, 2022 at 7:17
Strings in python are unmutable, besides, need to reassign the variable — Dani Mesejo
– Dani Mesejo, Commented Jul 20, 2022 at 7:17

echo encrypt · Accepted Answer · 2022-07-20 07:19:23Z

2

maybe you need add + characters before =

txt = input()
modified_txt = ""

for char in txt:
    if char.isupper():
        modified_txt += "u"
    elif char.islower():
        modified_txt += "l"
    else:
        modified_txt += "-"

print(modified_txt)

answered Jul 20, 2022 at 7:19

echo encrypt

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1 Comment

matszwecja Over a year ago

Didn't you mean " = characters after +"?

niaei · Accepted Answer · 2022-07-20 07:21:50Z

2

A string is an immutable data type. So + is not an inplace operation for a string.

You need to reassign your variable with the new values. So change the lines:

modified_txt + SOMETHING

to

modified_txt = modified_txt + SOMETHING

or as Matiiss suggested to:

modified_txt += SOMETHING

edited Jul 20, 2022 at 7:21

answered Jul 20, 2022 at 7:19

niaei

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3 Comments

Matiiss Over a year ago

I didn't exactly suggest it... it's just something that one should really use instead of that extended thing (which can be used to explain what += does but not really used because, well, there's a shorter option that everyone uses)

niaei Over a year ago

@Matiiss I know people (such as myself) who prefer the first method. Because I think the first method is more readable. But you're absolutely right. One should know.

matszwecja Over a year ago

+ shouldn't be in-place operation even for mutable types. That's what += is for. a + b on its own in a line of code pretty much never makes sense.

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