Find First Non-Repeating Character from a Stream in Python

In this article, we will find the first non-repeating character from a stream of character. Let's say the following is our input ?

Thisisit

The following should be our output displaying first non-repeating character ?

H

Find the first non-repeating character from a stream of characters using while loop

We will find the first non-repeating character, by comparing each character with the other using a loop ?

Example

# String
myStr = "thisisit"

# Looping
while myStr != "":
	slen0 = len(myStr)
	ch = myStr[0]
	myStr = myStr.replace(ch, "")
	slen1 = len(myStr)
	if slen1 == slen0-1:
		print ("First non-repeating character = ",ch)
		break;
	else:
		print ("No Unique Character Found!")

Output

No Unique Character Found!
First non-repeating character =  h

Find the first non-repeating character from a stream of characters using a function

We can also create a custom function and pass the string to it for finding the first non-repeating character ?

Example

# Custom function
def RepeatingFunc(myStr):
	char_order = []
	counts = {}

	for c in myStr:
		if c in counts:
			counts[c] += 1
		else:
			counts[c] = 1
			char_order.append(c)
	for c in char_order:
		if counts[c] == 1:
			return c
	return None

print("First Non-Repeating Character = ",RepeatingFunc('thisisit'))

Output

First Non-Repeating Character =  h

Find the first non-repeating character from a stream of characters using Counter()

The Counter can also be used from the Collections module to find the first non-repeating character. This module implements specialized container datatypes providing alternatives to Python's general purpose built-in containers, dict, list, set, and tuple ?

Example

from collections import Counter

def repeatFunc(myStr):

	freq = Counter(myStr)

	# Traverse the string
	for i in myStr:
	    if(freq[i] == 1):
		    print(i)
		    break

# Driver code
myStr = "thisisit"

repeatFunc(myStr)

Output

h