a questions about thread-safety of boolean variables

[Charlie Dickens]

Hi,if I have a class A that contains a boolean variable named x, is it safe
to read and change it from different threads without using locks?
Is it guaranteed that A.x will be always True or False, and not any other
weird value that that causes it to be inconsistent (assuming I only set it
to True or False) ?

I have a = A()
first thread does:
if a.x is True :
    pass

2nd thread does:
a.x = False

is it safe?

and what if x was a dict ? especially if the only values that are set in the
dictionary are simple: booleans, integers, floats, strings
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