refactor __eq__ and __hash__ methods

[CunliangGeng]

Follow the guide to refactor __hash__ and __eq__ methods in all relevant classes.

https://docs.python.org/3.10/glossary.html

hashable:
An object is hashable

• if it has a hash value which never changes during its lifetime (it needs a hash() method),
• and can be compared to other objects (it needs an eq() method).
  Hashable objects which compare equal must have the same hash value.

Hashability makes an object usable as a dictionary key and a set member, because these data structures use the hash value internally.

Most of Python’s immutable built-in objects are hashable; mutable containers (such as lists or dictionaries) are not; immutable containers (such as tuples and frozensets) are only hashable if their elements are hashable. Objects which are instances of user-defined classes are hashable by default. They all compare unequal (except with themselves), and their hash value is derived from their id().