removing "y" immediately before or after any vowel in a string in python

Question

I want to remove vowels in a string, for simplicity I have only included small letters in below code

for x in "aeiou":
  st = st.replace(i,"")
  return st

this is working fine, however i am wondering how to approach the scenario where I want to also remove y in a string including vowels if it has any vowel to the left or right e.g after running the function on "may" it should return "m", similarly "mystery" to "mystry".

Answer 1

This is probably a homework assignment, but really the simplest (although not necessarily the fastest one) would be using regex:

import re
p = re.compile(r'(?i)y?[aeiou]y?')

p.sub('', 'may')
# 'm'

p.sub('', 'mystery')
# 'mystry'

---

Using pure python, you can listify your string, iterate over each character, remove characters accordingly (yes, you have done this, so you will need to modify your existing code using if statements to account for the case of "y"), and rejoin back. Here's an example.

def remove_vowels_with_y(string):
    # Cache vowel set for better lookup performance.
    v = set('aeiouAEIOU')
    # Listify your string. This is because strings are immutable.
    chars = list(string) + [''] # Sentinel character.
    # Initialization.
    filtered = []
    prev_is_vowel = False
    for i, c in enumerate(chars[:-1]): 
        # Add elements to `filtered` if conditions are met.
        if not (c in v or (c in 'yY' and (prev_is_vowel or chars[i+1] in v))):
            filtered.append(c)
        prev_is_vowel = c in v

    # Join filtered list and return result.    
    return ''.join(filtered)

remove_vowels_with_y('may')
# 'm'

remove_vowels_with_y('mystery')
# 'mystry'