join with outer join support

join.py

def join(t,col,rt,rcol=None,outer=False):
    if not rcol:
        rcol = col
    for entry in t:
        matches = [d for d in rt if d[rcol] == entry[col]]
        for match in matches:
            yield entry,match
        if len(matches) == 0 and outer:
            yield entry,None