Singleton-comparison suggestion by pylint

Question

For the given code

def greater(n):
    if n > 3:
        res = True
    else:
        res = False

    return res

a = greater(5)
print(hex(id(a)))
print(hex(id(True)))

b = True
print(hex(id(b)))

if  a == True:
    print('yes')
else:
    print('no')

pylint suggests pylint_example.py:16:4: C0121: Comparison 'a == True' should be 'a is True' if checking for the singleton value True, or 'a' if testing for truthiness (singleton-comparison)

a is True will check both address and value
and I cannot assume immutable variables will have the same address

Thus, changing a == True to a is True may lead to incorrect results (a and True may have different addresses in memory). Why does pylint suggest that?

Though

print(hex(id(a)))
print(hex(id(True)))

b = True
print(hex(id(b)))

part gives consistent results. I am not sure if that would work in general.

Asked By: Chungji

||

Source

Answer 1

PEP 8 claims that correct way is to use if variable giving following example

if greeting:

and claims that

if greeting == True:

is wrong and

if greeting is True:

is worse.

Answered By: Daweo

Answer 2

True and False are unique singletons, not immutable. If a has the value True, then a and True do have the same memory address.

Source: PEP-0285 and In Python are the built in constants True and False unique?

Answered By: Dash

Singleton-comparison suggestion by pylint

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