Check if a string is Isogram or not in Python

An isogram is a string where each letter appears exactly once. In Python, we can check if a string is an isogram using various approaches like sets, lists, or built-in functions.

For example, "education" is an isogram because each letter (e, d, u, c, a, t, i, o, n) appears only once.

Method 1: Using a List to Track Characters

We can iterate through each character and maintain a list of seen characters ?

def check_isogram_with_list(word):
    char_list = []
    for char in word:
        if char.isalpha():
            if char.lower() in char_list:
                return False
            char_list.append(char.lower())
    return True

# Test the function
s = "education"
print(f"'{s}' is isogram:", check_isogram_with_list(s))

s = "hello"
print(f"'{s}' is isogram:", check_isogram_with_list(s))

'education' is isogram: True
'hello' is isogram: False

Method 2: Using a Set for Efficient Lookup

Sets provide O(1) lookup time, making this approach more efficient ?

def check_isogram_with_set(word):
    seen_chars = set()
    for char in word:
        if char.isalpha():
            char_lower = char.lower()
            if char_lower in seen_chars:
                return False
            seen_chars.add(char_lower)
    return True

# Test the function
test_words = ["education", "programming", "Python", "123abc"]

for word in test_words:
    result = check_isogram_with_set(word)
    print(f"'{word}' is isogram: {result}")

'education' is isogram: True
'programming' is isogram: False
'Python' is isogram: True
'123abc' is isogram: True

Method 3: Using Set Length Comparison

Compare the length of original alphabetic characters with unique characters ?

def check_isogram_set_length(word):
    # Extract only alphabetic characters and convert to lowercase
    alpha_chars = [char.lower() for char in word if char.isalpha()]
    # Compare length of list with set (unique characters)
    return len(alpha_chars) == len(set(alpha_chars))

# Test with various strings
test_cases = ["education", "Hello", "Programming", "abcdef", ""]

for test in test_cases:
    result = check_isogram_set_length(test)
    print(f"'{test}' is isogram: {result}")

'education' is isogram: True
'Hello' is isogram: False
'Programming' is isogram: False
'abcdef' is isogram: True
'' is isogram: True

Comparison

Key Points

• Use char.lower() to handle case-insensitive comparison
• Use char.isalpha() to ignore non-alphabetic characters
• Set-based approaches are more efficient for larger strings
• Empty strings are considered isograms by definition

Conclusion

Use the set length comparison method for the most concise and efficient solution. The set lookup method offers good performance with clear logic, while the list method is useful for understanding the concept step by step.