Sympy
SymPy is a Python library for symbolic mathematics. It aims to become a full-featured computer algebra system (CAS) while keeping the code as simple as possible in order to be comprehensible and easily extensible. SymPy is written entirely in Python.
Packages that use SymPy
Official documents
SymPy Tutorial
Tutorials
Tips
SymPy simplify does not attempt factoring - Stack Overflow
Simplify sympy.KroneckerDelta - Stack Overflow