Scrub with a regex

Isogram
Isogram in Python 
import re


def is_isogram(phrase):
    scrubbed = re.compile('[^a-zA-Z]').sub('', phrase).lower()
    return len(set(scrubbed)) == len(scrubbed)

For this approach, regular expression, also known as a regex, is used to scrub the input phrase string.

  • In the pattern of [^a-zA-Z] the brackets are used to define a character set that looks for characters which are not a through z and A through Z.
Note

If the first character of a character set is ^, all the characters that are not in the rest of the character set will be matched.

This essentially matches any characters which are not in the English alphabet. The pattern is passed to the compile() method to construct a regular expression object.

  • The sub() method is then called on the regex object. The sub() method replaces all non-alphabetic characters in the input phrase with an empty string.
  • The output of sub() is then chained as the input for lower(). All of the letters are lowercased so that letters of different cases will become the same letter for comparison purposes, since A and a are considered to be the same letter. When the replacing and lowercasing is done, the scrubbed variable will be a string having all alphabetic letters lowercased.
  • A set is constructed from the scrubbed string and its len is compared with the len of the the scrubbed string. Since a set holds only unique values, the phrase will be an isogram if its number of unique letters is the same as its total number of letters. The function returns whether the number of unique letters equals the total number of letters.
  • For Alpha it would return False, because a is considered to repeat A, so the number of unique letters in Alpha is 4, and the total number of letters in Alpha is 5.
  • For Bravo it would return True, since the number of unique letters in Bravo is 5, and the total number of letters in Bravo is 5.
4th Dec 2024 · Found it useful?

Other Approaches to Isogram in Python

Other ways our community solved this exercise
def is_isogram(phrase):
    scrubbed = [ltr.lower() for ltr in phrase if ltr.isalpha()]
    return len(set(scrubbed)) == len(scrubbed)
Scrub with a list comprehension

Use a list comprehension and set to return the answer. 

def is_isogram(phrase):
    scrubbed = phrase.replace('-', '').replace(' ', '').lower()
    return len(scrubbed) == len(set(scrubbed))
Scrub with a series of replace calls

Use a series of replace calls and set to return the answer. 

import re


def is_isogram(phrase):
    scrubbed = "".join(re.findall("[a-zA-Z]", phrase)).lower()
    return len(set(scrubbed)) == len(scrubbed)
Use re.findall to get valid letters

Use a re.findall and set to return the answer. 

for ltr in phrase:
    letter = ord(ltr)
    if letter >= A_LCASE and letter <= Z_LCASE:
        if letter_flags & (1 << (letter - A_LCASE)) != 0:
            return False
        else:
            letter_flags |= 1 << (letter - A_LCASE)
Bit field using a for loop

Use a bit field with a for loop to keep track of used letters.