input: Write a Python function to determine the count of alphabetic characters and digits in a given string.  
  assert dig_let("python")==(6,0)  
  assert dig_let("program")==(7,0)  
  assert dig_let("python3.0")==(6,2)
output: def dig_let(s):
      letters = sum(c.isalpha() for c in s)
      digits = sum(c.isdigit() for c in s)
      return letters, digits