https://cv-tricks.com/how-to/developer-guide-to-key-differences-between-python-2-and-3/

• • Print Statement
  • input() function (returns a string in 3.x; under 2.x use raw_input instead)
  • Unicode Literals
  • Exceptions
  • Rounding
  • List comprehension
  • Generators
  • string.replace is not available anymore
  • reload() should be replaced with import importlib; importlib.reload()
  • As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered but insertion ordered.

https://medium.com/@meghamohan/mutable-and-immutable-side-of-python-c2145cf72747

Everything in Python is an object.
Since everything in Python is an Object, every variable holds an object instance. When an object is initiated, it is assigned a unique object id. Its type is defined at runtime and once set can never change, however its state can be changed if it is mutable.

Simply put, a mutable object can be changed after it is created, and an immutable object can’t.

Mutable objects:
list, dict, set, byte array

Immutable objects:
int, float, complex, string, tuple, frozen set [note: immutable version of set], bytes