Replacing part of a string using a For loop

Question

I need to get a user to enter a sentence for an assignment. Using a for loop, I then need to replace all spaces with %20 in order to prep the string to be used as a URL. I cannot for the life of me figure it out.

sentence = str(input("Please enter sentence:"))
space = (" ")

for space in sentence:
    space.replace(sentence, space, "%20", 500)
print(sentence)

This is what I have entered so far but it is completely wrong.

You did it the "right" way. This is not a very good use case for for loops. — Mad Physicist, Nov 13 '18 at 22:29
Strings are immutable, `replace` returns a new string, it doesn't modify the string in place. — Barmar, Nov 13 '18 at 22:30
@Barmar. While I mostly agree with closing this question, I don't think that you have chosen a valid duplicate. OP is asking about replacing characters using loops. URLs are totally incidental here. — Mad Physicist, Nov 13 '18 at 22:33
@roganjosh. Odd, as I'm on mobile. I swear that usually doesn't happen :) — Mad Physicist, Nov 13 '18 at 22:34
@MadPhysicist The only reason he's trying to replace characters is because he wants to do url-encoding. — Barmar, Nov 13 '18 at 22:34
@Barmar. The only reason he's trying to replace characters is because his teacher told him to, and his teacher is focusing of for loops right now. — Mad Physicist, Nov 13 '18 at 22:35

score 2 · Answer 1 · answered Nov 13 '18 at 22:41

2

String in Python can't be modified. The replace() function returns a new string with all the replacements done. You need to assign this result somewhere. So you can do:

sentence = sentence.replace(" ", "%20")

If you want to do it with a loop, you need to build the result in another variable.

new_sentence = ""
for char in sentence:
    if char == " ":
        new_sentence += "%20"
    else:
        new_sentence += char

There's no point in using replace() in the loop.

answered Nov 13 '18 at 22:41

Barmar

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I swear I didn't copy your answer. – mRotten Nov 13 '18 at 22:47
Good job renaming the variables when you did it. :) – Barmar Nov 13 '18 at 22:48
Ha! Yeah, I had to, otherwise it would have been obvious. – mRotten Nov 13 '18 at 22:50
Thanks guys appreciate your help. – k.dochertyy Nov 14 '18 at 09:33

score 1 · Answer 2 · answered Nov 13 '18 at 22:44

1

Replace everything after the first line with print(sentence.replace(" ","%20"))

or, if you really must use a loop:

s = ''
for x in sentence:
    if x == ' ':
        s += "%20"
    else:
        s += x
print(s)

answered Nov 13 '18 at 22:44

mRotten

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score 0 · Answer 3 · answered Nov 13 '18 at 23:20

you've got a few problems here:

the variable space that you define before the loop is equal to " " but then you're using the same name for the for loop variable, which is going to iterate through the string the sentence string, in the loop, it's going to use the value defined by the loop.
You're giving the replace method too many arguments, it's a method of the string object so you don't need to pass it the large string to operate on Replace Method
You're using the replace method on the space string and not on the sentence string

Good way to do it in real life:

old = ' '  
new = '%20'

sentence = str(input("Please enter sentence:"))
print(sentence.replace(old,new))

The way your teacher is probably after:

sentence = str(input("Please enter sentence:"))
old = ' '  
new = '%20'
newSentence = ''

for letter in sentence:
    if letter == ' ':
        newSentence += new
    else:
        newSentence += letter


print(newSentence)

Hi Kieran, Thanks for your help. Not only does the code work and it is 100% in line with what my lecturer is looking for. it all makes a lot of sense and has really cleared up the problem in my head. thanks :D — k.dochertyy, Nov 14 '18 at 09:32

Replacing part of a string using a For loop

3 Answers3