Incomplete contract in HumanEval #160 (do_algebra)

[mrigankpawagi]

We need to check for possible ZeroDivisionErrors. Maybe something like the following will be okay.

...
try:
    return eval(exp)
except ZeroDivisionError:
    assert False, "invalid inputs" # $_CONTRACT_$

Alternatively,

assert not any([operand[i-1] == 0 and operator[i] == "//" for i in range(1, len(operand))]), "invalid inputs" # $_CONTRACT_$

may also work.