Why adding to specific index to a list result adding to all the indexes

Question

https://code.sololearn.com/clhei9EJ2qQL/?ref=app

Answer 1

I forget what it is called but there's something within python that remembers the *3 at the creation of your matrix. It applies that multiplication to all subsequent instructions.

Answer 2

@Grahambo would you give me any link that explains it

Answer 3

https://docs.python.org/2/library/stdtypes.html#sequence-types-str-unicode-list-tuple-bytearray-buffer-xrange