splits = re.split(r'(\d.*)', op)

This regular expression will split the string "op" into a list of substrings at every occurrence of a digit followed by any characters. The parentheses around "\d.*" create a capturing group that includes the digit and any characters that follow it. The "r" before the string indicates that it is a raw string, which means that backslashes are treated as literal characters rather than escape characters.

For example, if "op" was the string "1+2*3-4/5", the resulting "splits" list would be:
["", "1", "+2", "*", "3", "-4", "/", "5", ""]

Note that the empty strings at the beginning and end of the list are a result of the splitting occurring at the start and end of the string.