The code for dict_equal() in Objects/dictobject.c currently loops over the key/value pairs in self and uses PyDict_GetItem() to check for the corresponding key/value pair in the other dictionary. This causes an unnecessary call to PyObject_Hash(). Instead, the code should loop over the key/value/hash triplets in self and do a direct lookup in the other dictionary with " ep = (otherdict->ma_lookup)(otherdict, key, hash)". The reuses the known hash value for the key; thereby avoiding the potentially slow call to PyObject_Hash(). See _PyDict_Contains() for an example of how to do a lookup when the hash value is already known. Note, the optimized path should be used only when PyDict_CheckExact() is true.
Here is a simple patch. > Note, the optimized path should be used only when PyDict_CheckExact() is true. Actually this is not needed. dict_equal() uses the same code for dict subclasses.
And here is a synthetic microbenchmark: $ ./python -m timeit -s "n=10**3; k=2; a={(i,)*k:i for i in range(n)}; b={(i,)*k:i for i in range(n)}" "a == b" Vanilla: 251 usec per loop Patched: 195 usec per loop $ ./python -m timeit -s "n=10**3; k=2; a={(i,)*k:i for i in range(n)}; b=dict(a)" "a == b" Vanilla: 116 usec per loop Patched: 58.6 usec per loop The use of tuple keys is quite common.
