Removing duplicates in Python

Question

My program so far

def RemoveDuplicates(text):
 result=[]
 used=set()
 for char in text:
 if char not in used:
 used.add(char)
 result.append(char)
 return ''.join(result)
text=input('Enter some text: ')
print(join(result))

I'm a beginner to Python so this is a quite difficult task for me. I know this doesn't add up, but where have I made the mistake?

• Moishe Lettvin: It doesn't look like you're ever calling RemoveDuplicates in your sample code.
• Oleh Prypin: Well, Python doesn't have any magic. You can't write random stuff and hope it will work.

Answer 1

You've never actually called your RemoveDuplicates() function.

Replace:

text=input('Enter some text: ')
print(join(result))

with:

print(RemoveDuplicates(input("Enter some text:" )))

• Oleh Prypin: @user1248367: It could be written even in one line, but with worse performance. The function seems good.
• kindall: Oh there are plenty of ways to write that shorter -- in one or two lines, in fact. But it's homework and what you have works, so I'd turn it in. :-)

Answer 2

In addition to the other answers: if you're using Python 2, you need to use raw_input instead of input.

Answer 3

A few things here:

1. You defined the function RemoveDuplicates, but never actually call it.

2. You use a set(), but then check for duplicates manually. A set, by definition, will get rid of duplicates automatically.

3. You haven't told us what you are actually trying to accomplish. Do that, then we can help you more.

• jdi: Although since he is trying to remove duplicate characters from a string, a set() would not maintain sort order
• user1248367: Sorry. I want the program to ask the user to enter some text. The output should be the text with duplicates removed. Text entered: "Stackoverflow", Output: Stackoverflw
• kindall: I'm pretty sure the set is being used manually because it's necessary to retain the order of the original text.
• Marius: I think the if char not in used: test is still redundant, which is the point @jwd was tring to make.
• jwd: @Marius: Well, the test isn't needed in order to do used.add(char), but it is still needed for the result.append(char). I was misunderstanding at first.

Answer 4

Your function looks okay to me, although I'm no expert. I think the problem lies in the fact that you're not actually calling it anywhere. Try calling it like this: print(RemoveDuplicates(text)).

Answer 5

One small problem is that you forgot to call your function! Additionally, if you're using Python 2.x the user input needs to be collected using raw_input.

Two small fixes and your code works fine:

def RemoveDuplicates(text):
 result=[]
 used=set()
 for char in text:
 if char not in used:
 used.add(char)
 result.append(char)
 return ''.join(result)
text = raw_input('Enter some text: ')
print(RemoveDuplicates(text))

• Casey Kuball: raw_input is python 2. It was renamed to input for python 3.x.