E.g. in Python:

def count_digit(number, digit, base=10, from_base=10):
  ...
  
count("133", "3")  # is the same as count("133", "3", 10, 10)

# so you don't need to convert the number
#                                vv
# and the digit 3 is 2 times in 133
# therefore the result is 2

Regards,

suic