Why doesn't calling a Python string method do anything unless you assign its output?
Solution 1:
This is because strings are immutable in Python.
Which means that X.replace("hello","goodbye")
returns a copy of X
with replacements made. Because of that you need replace this line:
X.replace("hello", "goodbye")
with this line:
X = X.replace("hello", "goodbye")
More broadly, this is true for all Python string methods that change a string's content "in-place", e.g. replace
,strip
,translate
,lower
/upper
,join
,...
You must assign their output to something if you want to use it and not throw it away, e.g.
X = X.strip(' \t')
X2 = X.translate(...)
Y = X.lower()
Z = X.upper()
A = X.join(':')
B = X.capitalize()
C = X.casefold()
and so on.
Solution 2:
All string functions as lower
, upper
, strip
are returning a string without modifying the original. If you try to modify a string, as you might think well it is an iterable
, it will fail.
x = 'hello'
x[0] = 'i' #'str' object does not support item assignment
There is a good reading about the importance of strings being immutable: Why are Python strings immutable? Best practices for using them