[akiselev]

It's more subtle than than "no side effects". Take Python prior to version 3, for example, which made possible the most egregious violation of referential transparency I've ever seen: `True, False = False, True`

Python code (pre-v3) that branches cannot be referentially transparent by definition because runtime context (the state of True/False bindings) is a hidden input in every boolean expression. You could have millions of lines of side effect free code and it will break completely if that one statement is run before the rest of the code.

Programmers depend on the referential transparency of keywords like "true", "false", "for", etc whether they're writing pure functional code or imperative spaghetti messes.