import re


def clump_fractions(s):
    """
    Replaces the whitespace between the integer and fractional part of a quantity
    with a dollar sign, so it's interpreted as a single token. The rest of the
    string is left alone.

        clump_fractions("aaa 1 2/3 bbb")
        # => "aaa 1$2/3 bbb"
    """
    return re.sub(r"(\d+)\s+(\d)/(\d)", r"\1$\2/\3", s)