from string import ascii_lowercase
''.join(c for c in 'my new absolutely c00l string' if c not in set(list(ascii_lowercase)) - set(list('aeiou')))

  
>>> s = 'abc 123 def 456 ghi'
>>> 
>>> pred = lambda i: i not in set('bcdfghjklmnpqrstvwxz')
>>> out = ''.join(filter(pred, s))
>>> out
'a 123 e 456 i'
>>>

 from random import randint
from string import ascii_lowercase
   
FULL_CONSONANTS = set(list(ascii_lowercase)) - set(list('aeiou'))
SEMIVOWELS = set(list('yw'))
   
def remove_consonants(string):
    '''The most perfect consonants removal ever'''
       
    return ''.join(c for c in string if c not in FULL_CONSONANTS or c in SEMIVOWELS and randint(0, 1))
   
>>> remove_consonants('my new absolutely c00l string')
' e aouey 00 i'
>>> remove_consonants('abc 123 def 456 ghi')
'a 123 e 456 i'