Juxtaposition is not multiplication in this context - you can't write (2 3), for example, it has to be (2 * 3).

Furthermore, Python already uses * for strings to indicate repetition: ("foo" * 2 == "foofoo").

String concatenation really just needs its own separate operator. & is an obvious candidate, if only it wasn't so commonly appropriated for bitwise AND - which is a very poor use of a single-char operator as it's not something that you need often, especially in a language like Python.

On the other hand, D uses binary ~ for concatenation. That has a neat mnemonic: it's a "rope" that "ties strings together".