Describe the differences between deep copy and shallow copy when writing code in Python.

"Shallow copy is a technique used to create new instance types while maintaining the original ones. It copies both the reference pointers and the values of the original. Deep copy is used to store values that have already been copied. It does not copy the reference pointers. The key difference between these is that changes made with shallow copy will update all the instances, while those made with deep copy will not be affected if changes are made in the original copy. When executing a program, shallow copy was faster than deep copy."