Dark magic

A 1-post collection

Block scoping in Python

Python uses function-level scoping, for most cases:

def f():
	x = 6
    if x > 0:
    	y = 5
    print(y)  # This works, even though `y` was declared inside the `if`

A variable declared anywhere outside a function is in the (module's) global scope, and a variable declared inside a function is in that function's scope except exceptions in except blocks since it would create GC cycles and comprehension expressions because those behave like functions ; blocks like conditionals and loops don't have their own scope like in C-family languages such as C, C++, Java, etc.

JavaScript, famously, also historically used function scoping, with var, though block scoping has been introduced in ES6 with the keywords let and const. Python doesn't have declarations though, so there's no real way to properly retrofit that onto the language, so we're still stuck with function scoping. Whether it's a good feature or not is outside the scope (got it?) of this blogpost.

Python's scoping is quite coherent with the absence of declarations, how would you do something like this:

if cond:
	x = 5
	x = 6

If variables had to be declared, you'd have to resort to tricks like writing x = None beforehand, but this messes