check if bytes is all nulls

[MRAB]

On 2018-04-01 18:55, Arkadiusz Bulski wrote:
> What would be the most performance efficient way of checking if a bytes is
> all zeros? Currently its `key == b'\x00' * len(key)` however, because its
> Python 2/3 compatible:
> 
> sum(key) == 0 is invalid
> key == bytes(len(key)) is invalid
> 
> I already considered precomputing the rhs value.
> Length of key is unknown, could be few bytes, could be megabytes.
> 
Have you tried:

not key.lstrip(b'\x00')

? (Although the result of the lstrip could be as long as the original.)

Or:

set(key) == set(b'\x00')

? (The set will never have more than 256 members.)