How come a variable in a function is able to reference from outside it's scope?-CodePudding

In this case, the "all_lines" variable is initalised in the context manager, and it is accessible from the function "part_1".

total = 0
with open("advent_input.txt", "r") as txt:
    all_lines = []
    context_total = 0
    for line in txt:
        all_lines.append((line.rstrip().split(" ")))


def part_1():
    # total = 0
    for line in all_lines:
        if line[0] == "A":
            if line[1] == "Y":
                total  = 8
            elif line[1] == "X":
                context_total  = 4

However, "context_total", which is also initalised in the context manager, does not work in the function "part_1". And "total" from the global scope does not work either. How come "all_lines" works?

CodePudding user response：

Python does not have general block scope, so anything assigned within the with will be accessible outside of the block.

context_total is different though since you're reassigning it within the function. If you assign within a function, the variable will be treated as a local unless you use global to specify otherwise. That's problematic here though since = necessarily must refer to an existing variable (or else what are you adding to?), but there is no local variable with that name.

Add global context_total to use it within the function, or pass it in as an argument if you don't need the reassigned value externally.

CodePudding user response：

It works because inside the function, the all_lines variable is referenced but not assigned. The other two variables are assigned.

If a variable is assigned inside a function, then that variable is treated as local throughout the function, even if there is a global variable of the same name.