Task:

Write a function that removes every lone 9 that is inbetween 7s.

Examples:

seven_ate9('79712312') => '7712312'
seven_ate9('79797') => '777'

Kata's link: SevenAte9

Best Practices

Py First:

def seven_ate9(str_):
   while str_.find('797') != -1:
       str_ = str_.replace('797','77')
   return str_

Py Second:

import re

def seven_ate9(str_):
    return re.sub(r'79(?=7)', r'7', str_)

Py Third:

seven_ate9 = lambda s:''.join(x for i, x in enumerate(s) if s[i-1:i+2] != "797")