Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #197793

Python __hash__ return value - what use is it?

Show all headers | View raw

1. So I am returning 1 for every instance of MyClass and then inserting 
the instances into a set. However when I print the set I see individual 
instances though I want the instances to be the treated the same .ie there 
should be just one instance in the set because the return value from 
__hash__ is always 1.

In the dictionary when I print it I see the instances as individual keys 
though I want to see a single key - what gives?? Why is the return value 
of __hash__ being ignored?? (I can see it's being called)

2. When is __eq__ used? If I have two instances and want to make them 
equal - what's the use case?

#!/usr/bin/python

class MyClass:
    def __bool__(self):
        print('in __bool__')
        return True

    def __hash__(self):
        # hash value is not a key
        print('in __hash__')
        return 1

    def __eq__(self, val):
        print('in __eq__', val)
        return True

c = MyClass()
d = MyClass()

if c:
    print("true")

print('-----')
s = set()
s.add(c)
s.add(d)
print(s)

print('-----')
d = { c : "10", d : "20"  }
print(d)

Back to comp.lang.python | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

Python __hash__ return value - what use is it? Veek M <veekjunk@foobar.com> - 2026-05-31 08:28 +0000
  Re: Python __hash__ return value - what use is it? Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-05-31 09:25 +0000
    Re: Python __hash__ return value - what use is it? Veek M <veekjunk@foobar.com> - 2026-05-31 10:13 +0000
  Re: Python __hash__ return value - what use is it? ram@zedat.fu-berlin.de (Stefan Ram) - 2026-05-31 09:40 +0000
  Re: Python __hash__ return value - what use is it? Jon Ribbens <jon+usenet@unequivocal.eu> - 2026-05-31 13:06 +0000

csiph-web