[Python] Custom type object tests as member of sequence but not of dictionary

As per the official Python docs for in operator:

For container types such as list, tuple, set, frozenset, dict, or collections.deque, the expression x in y is equivalent to any(x is e or x == e for e in y).
​

However this does not seem to be true. Please see the following code:

class Val:
def __init__(self, val):
self.val = val
def __eq__(self, other):
return self.val == other.val
__hash__ = object.__hash__

one = Val(1) ; two = Val(2) ; three = Val(3)

valSeq = [one, two, three]

print("Val(2) in valSeq:\n ", Val(2) in valSeq)


This prints:

Val(2) in valSeq:
True


as expected, but the same does not work when I use Val as a key in a dictionary:

valMap = {one: "ekam", two: "dve", three: "trini"}

print("valMap[Val(2)]:")
try:
print(valMap[Val(2)])
except KeyError:
print(" KeyError")

print()

print("Val(2) in valMap:\n ", Val(2) in valMap)


This outputs:

valMap[Val(2)]:
KeyError

Val(2) in valMap:
False


To investigate why this happens, I try testing what the documentation says:

def inTest(obj, seq):
return any(obj is test or obj == test for test in seq)
print("inTest(Val(2), valMap):\n ", inTest(Val(2), valMap))


which gives:

inTest(Val(2), valMap):
True


and sure enough, the equality test of Val(2) is satisfied as expected:

def inTestStr(obj, seq):
for test in seq:
print(obj is test, obj == test)
print("inTestStr(Val(2), valMap):")
inTestStr(Val(2), valMap)


which gives:

inTestStr(Val(2), valMap):
False False
False True
False False


What is wrong and why doesn't in operator work as expected?

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