Two words are anagrams if you can make one from the other by rearranging its letters. For example, ‘listen’ and ‘silent’ use exactly the same letters, so they are anagrams. In this lesson you will write a Python program to check an anagram in three ways: by sorting, with Counter, and with a manual count. You will also handle capital letters and spaces.

Run the code in our online Python compiler. The compiler does not take keyboard input, so the examples use fixed values.

 

The logic

Two strings are anagrams when they contain the same letters the same number of times. There are two simple ways to check:

  1. Sort the letters of both strings. If the sorted results are equal, the strings are anagrams.
  2. Count how often each letter appears in both strings. If the counts match, they are anagrams.

 

Method 1: sort and compare

def is_anagram(a, b):
    return sorted(a.lower()) == sorted(b.lower())

print(is_anagram('listen', 'silent'))
print(is_anagram('hello', 'world'))
print(is_anagram('Dormitory', 'Dirty room'))

Output:

True
False
False

sorted() turns a string into a sorted list of its letters:

print(sorted('listen'))
print(''.join(sorted('silent')))
['e', 'i', 'l', 'n', 's', 't']
eilnst

Both ‘listen’ and ‘silent’ give the same list of letters, so they are anagrams.

The lower() call makes the check case-insensitive. Without it, ‘Listen’ and ‘Silent’ would not match, because capital letters sort before small letters:

print(sorted('Listen') == sorted('Silent'))
False

Anagrams with spaces and punctuation

The third example above printed False, but ‘Dormitory’ and ‘Dirty room’ are a famous anagram pair. The space in ‘Dirty room’ is counted as a character. Keep only letters and digits with isalnum():

def is_anagram(a, b):
    clean = lambda s: sorted(ch.lower() for ch in s if ch.isalnum())
    return clean(a) == clean(b)

print(is_anagram('Dormitory', 'Dirty room'))
print(is_anagram('Astronomer', 'Moon starer'))
print(is_anagram('abc', 'abd'))

Output:

True
True
False

Method 2: using Counter

The Counter class from the collections module counts how many times each item appears. Two strings are anagrams if their counts are equal.

from collections import Counter

print(Counter('listen') == Counter('silent'))
print(Counter('aab') == Counter('abb'))

Output:

True
False

This method is faster than sorting for long strings, because it does not need to sort.

 

Method 3: count the letters yourself

This version uses a dictionary, and shows what Counter does inside.

def is_anagram(a, b):
    if len(a) != len(b):
        return False

    counts = {}
    for ch in a:
        counts[ch] = counts.get(ch, 0) + 1

    for ch in b:
        if counts.get(ch, 0) == 0:
            return False
        counts[ch] -= 1

    return True

print(is_anagram('listen', 'silent'))
print(is_anagram('aab', 'abb'))
print(is_anagram('abc', 'abcd'))

Output:

True
False
False

The program counts each letter of the first word, then subtracts one for each letter of the second word. If a letter is missing or used up, the words are not anagrams. If the lengths are different, it returns False straight away.

 

Which method should you use?

Method

Code length

Best for

sorted()

Shortest

Exams, and most programs

Counter

Short

Long strings, and when you also need the counts

Manual dictionary

Longest

Understanding the idea

 

Take the words from the user (on your computer)

a = input('Enter the first word: ')
b = input('Enter the second word: ')

if is_anagram(a, b):
    print('Anagrams')
else:
    print('Not anagrams')

Our online compiler does not support input() yet, so use fixed values there.

 

Common mistakes

  • Forgetting lower(). ‘Listen’ and ‘silent’ do not match when the case is different.
  • Counting spaces and punctuation. Use isalnum() for sentences.
  • Comparing only the lengths, or only the sets of letters. set(‘aab’) and set(‘abb’) are equal, but the words are not anagrams.
  • Using sort() on a string. Strings have no sort() method. Use sorted().

 

Practice questions

  1. Check whether ‘Triangle’ and ‘Integral’ are anagrams.
  2. Group the words [‘listen’, ‘silent’, ‘enlist’, ‘google’, ‘gogole’] into anagram groups.
  3. Check whether a word is an anagram of its reverse.
  4. Count how many pairs of words in a list are anagrams.

 

FAQs

What is an anagram?

An anagram is a word or phrase made by rearranging the letters of another word or phrase, using every letter exactly once.

Are ‘listen’ and ‘silent’ anagrams?

Yes. Both use the letters e, i, l, n, s and t once each.

Is a word an anagram of itself?

By the usual definition, yes. The program above returns True for it, unless you add a rule to exclude identical words.

How do I check anagrams without sorting?

Use Counter or the dictionary method. Both count the letters instead of sorting them.

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