Associativity of “in” in Python?

Question

I\'m making a Python parser, and this is really confusing me:

>>>  1 in  []  in \'a\'
False

>>> (1 in  []) in \'a\'
TypeError: \'in &         


        

Answer 1

From the documentation:

Comparisons can be chained arbitrarily, e.g., x < y <= z is equivalent to x < y and y <= z, except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false).

What this means is, that there no associativity in x in y in z!

The following are equivalent:

1 in  []  in 'a'
# <=>
middle = []
#            False          not evaluated
result = (1 in middle) and (middle in 'a')


(1 in  []) in 'a'
# <=>
lhs = (1 in []) # False
result = lhs in 'a' # False in 'a' - TypeError


1 in  ([] in 'a')
# <=>
rhs = ([] in 'a') # TypeError
result = 1 in rhs