Count the number of Unique Characters in a String in Python

We are given a string, and our task is to find the number of unique characters in it. For example, if the string is "hello world", the unique characters are {h, e, l, o, w, r, d}, so the output should be 8.

Using set

Set in Python is an unordered collection of unique elements automatically removing duplicates when created from a string. The number of unique characters in string can be determined by finding length of set using len().

a = "hello world"

# Convert the string to a set
u_ch = set(a)

# Count the number of unique characters
u_c = len(u_ch)

print(f"Number of unique characters: {u_c}")

Number of unique characters: 8

Explanation:

• Code converts the string "hello world" to a set (set(a)) to extract unique characters as sets automatically remove duplicates.
• It calculates number of unique characters using len(u_ch) and displays count using a formatted string.

Using collections.Counter

collections.Counter counts character frequencies in a string and stores them as key-value pairs. The number of unique characters is length of Counter object representing distinct keys.

from collections import Counter

a = "hello world"
ch = Counter(a)
u_c = len(ch)

print(f"Number of unique characters: {u_c}")

Number of unique characters: 8

Explanation:

• Counter(a) counts the frequency of each character in string "hello world" and stores counts in a dictionary-like structure.
• Number of unique characters is determined using len(ch) which gives total number of distinct keys (characters) in Counter.

Using a manual loop

A manual loop iterates through each character in string and adds it to a list or set if it is not already present ensuring only unique characters are tracked. The number of unique characters is then determined by counting the length of resulting collection.

s = "hello world"
u_ch = []
for char in s:
    # If the character is not already in the list, add it
    if char not in u_ch:
        u_ch.append(char)

# Calculate the number of unique characters 
u_c = len(u_ch)
print(f"Number of unique characters: {u_c}")

Number of unique characters: 8

Explanation:

• Loop iterates through each character in the string and appends it to the u_ch list only if it hasn't been added before ensuring all characters are unique.
• Length of u_ch list is calculated using len() representing number of unique characters in string.