replace() 中的变量重用

Question

I have a simple replace() using a dict. This code is fully functional, but as soon as I change to a new variable name for the cleaned string, it stops working (step 2). My question is why I cannot create a new string (s2) in the second step?

words = {
    "badword": "niceword",
    "worseword": "nicerword"
    }
#step1
sentence = input(">")
for key, value in words.items():
    sentence = sentence.replace(key, value)
print(sentence)
#step2
sentence2 = input("s2>")
for key, value in words.items():
    s2 = sentence2.replace(key, value) #here
print(s2)

Answer 1

To keep the original string as well you'll have to copy the string before doing replacements, and then do the replacements on the copy.

s2 = sentence2 = input("s2>")

for key, value in words.items():
    s2 = s2.replace(key, value) #here

print(sentence2, s2)

Otherwise you're overwriting s2 in each iteration, using the unaltered sentence2 as your source - in effect only having the last iteration of the loop matter (which replaces worseword with nicerword .

With your original code each step of the loop looks like this, with "badword worseword" as input:

s2 = "badword worseword".replace('badword', 'niceword')

# s2 is now niceword worseword
# but since you're still using sentence2, which is "badword worseword", the second
# iteration will still use the original string and not the changed one:
s2 = "badword worseword".replace('worseword', 'niceword')

.. and now s2 is badword niceword - since you're not using s2 but sentence2 as the string you're replacing content in in your loop.

Answer 2

There is a problem with your logic.

You are doing it in two different ways

sentence = input(">")
for key, value in words.items():
    sentence = sentence.replace(key, value)

You replace something in sentence for each item in your dict

As in this block you are doing it the wrong way

sentence2 = input("s2>")
for key, value in words.items():
    s2 = sentence2.replace(key, value) #here
print(s2)

sentence2 is not the string that will be modified, you just save in s2 the result of sentence2.replace() So you overwrite s2 each time with the original inputstring.