Is there a better way to do this?

# src is a dictionary, each key's value is its relative probability as an arbitrary numeric value
items = []
weights = []
s = 0.0
for k, v in src.items():
    items.append(k)
    weights.append(v)
    s += v
weights = map(lambda x: x/s, weights)
numpy.random.choice(items, p=weights)