Editor

Python Program to Remove Duplicate Characters from a String

Beginner · Strings

This program removes repeated characters from a string and keeps only the first time each one appears, so "programming" becomes "progamin". The characters that remain stay in their original order.

Program

remove_duplicate_characters.py
text = "programming" # or: text = input("Enter a string: ")
result = ""
for ch in text:
if ch not in result: # keep only the first copy of each character
result += ch
print("Original: ", text)
print("Without duplicates:", result)
Output
Original:           programming
Without duplicates: progamin

How it works

  1. result starts empty and collects the characters to keep.
  2. if ch not in result checks whether the character has been kept already, so only new characters are added.
  3. Because the loop reads the string from left to right, the first copy of each character survives and later copies are dropped.
  4. The check is case-sensitive, so "P" and "p" count as different characters.

Other ways to write it

Using dict.fromkeys()

Using dict.fromkeys()
text = "programming"
result = "".join(dict.fromkeys(text))
print(text, "->", result)
Output
programming -> progamin

dict.fromkeys(text) makes a dictionary with each character as a key. Keys cannot repeat and keep the order they were added in, so joining them gives the answer in one line.

Using a set (the order is lost)

Using a set (the order is lost)
text = "programming"
unique = set(text)
print("Unique characters, sorted:", "".join(sorted(unique)))
print("Number of different characters:", len(unique))
Output
Unique characters, sorted: agimnopr
Number of different characters: 8

A set keeps one copy of each character but has no order, and the order of a set of strings can even change from one run to the next, so the result is sorted before printing.

Try it yourself

Change the check to ignore case, so that "Mississippi River" keeps only one i, one s and one r.

Edit the program above and press Run, or open it in the full editor to save it and share it. To watch it run line by line, open it in the visualizer.

Related programs

All Python programs · CBSE class 12 practical file · Python exercises