Different hash result in different versions

[MrTinkerman]

I'm working on code that calculates checksums for dictionaries. Since dicts are unordered I'm calculating the sum of hashes for the items (key-value pairs) in the dict as follows:

msg = {'a':10, 'b':20, 'c':30}
checksum = sum(hash(item) for item in msg.items())

#>>> 3023635889

This seemed to work fine until I started working on ESPnow between two boards, checksum errors...
Then I noticed the two boards have different Micropython versions.

# MicroPython v1.23.0 on 2024-06-02; Generic ESP32S3 module with ESP32S3


msg = {'a':10, 'b':20, 'c':30}
print(sum(hash(item) for item in msg.items()))

#>>> 3023635889

for item in msg.items():
    print(item, hash(item))
    
#>>> ('b', 20) 1007878631
#>>> ('c', 30) 1007878640
#>>> ('a', 10) 1007878618

# MicroPython v1.24.1 on 2024-11-29; Generic ESP32S3 module with ESP32S3


msg = {'a':10, 'b':20, 'c':30}
print(sum(hash(item) for item in msg.items()))

#>>> 3024170645

for item in msg.items():
    print(item, hash(item))
    
#>>> ('b', 20) 1008056883
#>>> ('c', 30) 1008056892
#>>> ('a', 10) 1008056870

I haven't flashed the boards with the same version yet, I guess that should resolve my issue.
But I'm curious about why this happens or if there's something else I'm missing.

Thanks.

EDIT:

I just flashed both boards to the same version and this version also produces different results from the other versions.
But hey, now both boards produce the same checksum.

But I'm still curious about why this happens.

# MicroPython v1.25.0 on 2025-04-15; Generic ESP32S3 module with ESP32S3


msg = {'a':10, 'b':20, 'c':30}
print(sum(hash(item) for item in msg.items()))

#>>> 3024176813

for item in msg.items():
    print(item, hash(item))
    
#>>> ('b', 20) 1008058939
#>>> ('c', 30) 1008058948
#>>> ('a', 10) 1008058926

[davefes]

Not sure if relevant, but ESP32 changed from Ordered dict to dict .... after v1.20 I think

[MrTinkerman]

Ok, so you mean the version 1.20 and below used ordered dicts?
If so I'd have to downgrade. But calculating the checksum like this works just fine if the versions match.

[davefes]

I think so, but I am no expert.

[bixb922]

In Python, hash() even varies each time you run Python. To have a stable hash, there is SHA256 in hashlib.

OrderedDict is available in the collections module.

Both modules are available in the standard ESP32 MicroPython images.

[peterhinch]

In Python, hash() even varies each time you run Python.

Interesting - so it does!

[adminpete@meerkat]: ~
$ upython 
MicroPython v1.25.0-dirty on 2025-04-16; linux [GCC 11.4.0] version
Use Ctrl-D to exit, Ctrl-E for paste mode
>>> 
paste mode; Ctrl-C to cancel, Ctrl-D to finish
=== msg = {'a':10, 'b':20, 'c':30}
=== print(sum(hash(item) for item in msg.items()))
=== 
284402678051021
>>> 
[adminpete@meerkat]: ~
$ upython 
MicroPython v1.25.0-dirty on 2025-04-16; linux [GCC 11.4.0] version
Use Ctrl-D to exit, Ctrl-E for paste mode
>>> 
paste mode; Ctrl-C to cancel, Ctrl-D to finish
=== msg = {'a':10, 'b':20, 'c':30}
=== print(sum(hash(item) for item in msg.items()))
=== 
296598340698317
>>> 

It's also very different on a 64-bit platform...

[MrTinkerman]

In Python, hash() even varies each time you run Python. To have a stable hash, there is SHA256 in hashlib.
...
Thanks.

But so far

sum(hash(item) for item in msg.items())

calculated identical checksum on two seperate boards.

I did switch to using hashlib/SHA256 though, just to be sure