import re


def findSubstring(a_string, substring):
    """assumes a_string is a string
    assumes substring is a string
    return a list of 2-tuples of ints, representing the span(s) where the substring is
    found, if it is found. Else returns an empty list"""
    pattern = substring
    results = re.finditer(pattern, a_string)
    spans = []
    for item in results:
        spans.append(item.span())
    return spans