The problem for Python with type checking is that the language has essentially no compile-time constructs at all, just a bunch of assignment operators with diff

The problem for Python with type checking is that the language has essentially no compile-time constructs at all, just a bunch of assignment operators with different syntax: `def` assigns a function object to a variable when it's executed, `import` assigns a module, `class` assigns a class object. This means that everything involving names in Python is just a variable lookup (incidentally, this is why a function call must follow the declaration in Python: the variable is unbound if you haven't executed the function definition yet). The reason `Sequence` fails in the example in the article is simply that the code is trying to read an unassigned variable, no different from writing `vairable` instead of `variable` in your code.