Just found some unintuitive behavior while competing in Google CodeJam.
input: pow(10, 20) in [pow(10, 20) * 1.0]
output: True
(ok...)
input: pow(10, 30) in [pow(10, 30) * 1.0]
output: False
(???????????)
(so uh, this behavior is dependent on the size of the number?!)
(is this because big Python integers are represented differently behind the scenes?)
input: True == True
output: False
(ok, all is normal)
input: pow(10, 20) in [pow(10, 20) * 1.0] == pow(10, 20) in [pow(10, 20) * 1.0]
output: False
(more ?????)
input: pow(10, 20) in [pow(10, 20) * 1.0] and pow(10, 20) in [pow(10, 20) * 1.0]
output: True
(and I'm totally lost)
That's because of floating point, and also because of the way python handles the result of exponentiation when integers are involved:
>>> type(pow(10,30))
<class 'int'>
the pow operator kept the result as integer.
Now if you multiply by 1.0 you force it to change representation to float, and then, with a 30 exponent, the precision isn't enough to compare to the same value as integer.
Unrelated but to fully answer your question, the strange behaviour with == is not related: it's a problem of operator chaining. Using a set of parentheses doesn't hurt and fixes your issue:
>>> pow(10, 20) in [pow(10, 20) * 1.0] == pow(10, 20) in [pow(10, 20) * 1.0]
False
>>> (pow(10, 20) in [pow(10, 20) * 1.0]) == (pow(10, 20) in [pow(10, 20) * 1.0])
True
>>>