Electrical resistors (3.5 points)

A company that makes electrical resistors uses codes to represent its products. These product codes include letters, digits and the following four special characters: '-', '_', '*' and '/'.

The head of the production department wants to know how many occurrences are in a product code following this pattern: a special character followed by a digit. For example in the product code '22-6489/4_97*ABC' there are three of such occurrences:'-6', '/4' and '_9'.

Write function resistor() that takes a product code (str) and returns the number of described occurrences (int) that contains.

Save this function in file resistor.py.

Examples:

>>> resistor('22-6489/4_97*ABC')
3
>>> resistor('21-AS*DF/3')
1
>>> resistor('21-AS*DF/X')
0

Note

More tests are provided in file test-resistor.txt.