CODEWITHSUNDEEP
pythonoperatorspython-3.7
talsegal
talsegal

Reputation: 543

python None and equals evaluation

If I run the following Python 3.7 code

a=None
b=None
a==b
>> True
b is not None
>> False
True is not None
>> True
a==b is not None
>> False

since a==b is True, this makes me understand this code evaluates as A==B where A=a and B=b is not None

However, if I run the following code

a = datetime(2020,1,1)
b = datetime(2020,1,1)
a==True
>> False
b is not None
>> True
a==b is not None
>> True

it contradicts the above. So I'm puzzled a bit with how all this is evaluated.

Thanks for your help!

Upvotes: 0

Views: 72

Answers (1)

ra1n
ra1n

Reputation: 71

you are seeing operator chaining in your example,

a==b is not None

is equivalent to:

a==b and b is not None

Thus the result.

If you want to compare a==b, use an atomic expression:

(a==b) is not None

See 6.10. Comparisons for details. In short, a op1 b op2 c ... y opN z is equivalent to a op1 b and b op2 c and ... y opN z, except that each expression is evaluated at most once.

Upvotes: 1

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