There's basically no performance difference between using a raw not (calling __bool__()) and is not (calling id(a) != id(b)). I only dropped the is because forcing the condition to check the boolean in this case simplifies the condition from a readability standpoint. We know that Null/None and '' both evaluate to False when __bool__() is called.
I wouldn't recommend this pattern when dealing with arbitrary objects (as the __bool__ method can be overwritten), but since we know the type signature of the input value is Optional(str), we can just use the raw `not`.
You could change the condition to be val is None or val == '', but why add a second condition when one will suffice? Since the condition will likely be short circuited anyways, we could write it in a way that reflects that and combines the checks into a single statement.
Testing:
from random import choice
opts = ["Something", "", None]
def raw_not():
val = choice(opts)
return not val
def is_not():
val = choice(opts)
return val is not None or val != ''
Disassembled:
raw_not
5 0 RESUME 0
6 2 LOAD_GLOBAL 1 (NULL + choice)
12 LOAD_GLOBAL 2 (opts)
22 CALL 1
30 STORE_FAST 0 (val)
7 32 LOAD_FAST 0 (val)
34 UNARY_NOT
36 RETURN_VALUE
-----------------------------------------------------------
is_not
9 0 RESUME 0
10 2 LOAD_GLOBAL 1 (NULL + choice)
12 LOAD_GLOBAL 2 (opts)
22 CALL 1
30 STORE_FAST 0 (val)
11 32 LOAD_FAST 0 (val)
34 LOAD_CONST 0 (None)
36 IS_OP 1
38 COPY 1
40 POP_JUMP_IF_TRUE 5 (to 52)
42 POP_TOP
44 LOAD_FAST 0 (val)
46 LOAD_CONST 1 ('')
48 COMPARE_OP 55 (!=)
>> 52 RETURN_VALUE
Performance:
%timeit raw_not()
298 ns ± 0.81 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops each)
%timeit is_not()
303 ns ± 5.04 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops each)
You can see that the python bytecode for the raw_not function is a lot simpler and only calls the UNARY_NOT function without adding any branching. Performance wise, it's a wash, but since there's branching in the short circuited version, the state of the data can effect the performance (checking for is None when most records are empty string will add an extra step for each record).
This is all beyond the scope for this question though lol, Everyone should definitely read PEP008, and do their best to abide by it, but I don't think that it should necessarily be used as gospel in all cases. Use your best judgement and if you feel that breaking PEP008 is valid in a certain case, make a note of it and be ready to justify it!
