I am trying to understand why the code behaves the way it does
class Baz():
def __init__(self,name):
self.name=name
k=[Baz(i) for i in range(4)]
print([hash(i) for i in k])
print([hash(Baz(i)) for i in range(4)])
This outputs
[8736683315973, -9223363300171459831, 8736683315982, -9223363300171459822]
[8736683315991, 8736683315991, 8736683315991, 8736683315991]
I'm wondering why in the second case I get all same hashcodes
If you don't define a __hash__ method in your class Python will use the memory address for the hashing.
In the second case Bash(i) isn't needed after the hash. Python throws it away and reuses the memory for the next Bash instance, so all subsequent calls get the same hash value.
class Baz():
def __init__(self,name):
self.name=name
print self
>>> k=[Baz(i) for i in range(4)]
print k
[<__main__.Baz instance at 0x7f5a010290e0>, <__main__.Baz instance at 0x7f5a01029908>, <__main__.Baz instance at 0x7f5a01028758>, <__main__.Baz instance at 0x7f5a0102e050>]`
k carry list of instances pass to class Baz with value 0, 1, 2, 3
here `self` have different object for `i` in `[hash(i) for i in k]`
if you then
print([hash(i) for i in k])
<__main__.Baz instance at 0x7f2ae9a13290>
<__main__.Baz instance at 0x7f2ae9a30908>
<__main__.Baz instance at 0x7f2ae9a300e0>
<__main__.Baz instance at 0x7f2ae9a35050>
[8738892813097, -9223363297961955184, 8738892820494, 8738892821765]
print([hash(Baz(i)) for i in range(4)])
see here, instance pass to class Baz is same. because hash uses same memory references and throws the previous memory reference for the instances.
<__main__.Baz instance at 0x7f2ae9a35290>
<__main__.Baz instance at 0x7f2ae9a35290>
<__main__.Baz instance at 0x7f2ae9a35290>
<__main__.Baz instance at 0x7f2ae9a35290>
[8738892821801, 8738892821801, 8738892821801, 8738892821801]
