Is there a way to use "static" variables in a function to return values later on?

I have the following input:

[['0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0'],
['0', '0', '10', '10', '0', '0', '10', '10', '0', '0', '0', '10', '10', '10', '10', '10', '0', '0', '0'],
['0', '0', '10', '10', '0', '0', '10', '10', '0', '0', '0', '0', '0', '0', '0', '10', '10', '0', '0'],
['0', '0', '10', '10', '0', '0', '10', '10', '0', '0', '0', '0', '0', '0', '0', '10', '10', '0', '0'],
['0', '0', '10', '10', '10', '10', '10', '10', '0', '0', '0', '0', '10', '10', '10', '10', '0', '0', '0'],
['0', '0', '0', '10', '10', '10', '10', '10', '0', '0', '0', '10', '10', '0', '0', '0', '0', '0', '0'],
['0', '0', '0', '0', '0', '0', '10', '10', '0', '0', '0', '10', '10', '0', '0', '0', '0', '0', '0'],
['0', '0', '0', '0', '0', '0', '10', '10', '0', '0', '0', '10', '10', '10', '10', '10', '10', '0', '0'],
['0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0'],
['0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0']]

For the following function:

def assign_points(lists):
"""
Assigns points from a list of lists to Vec4 objects.
...
"""
z_max = float('-inf')
z_min = float('inf')
points = []
for y, l in enumerate(lists):
for x, point in enumerate(l):
try:
z, color = parse_point(point)
if color is None:
color = no_color(z)
points.append(Vec4(x, y, z, 0, color))
# Update z_max and z_min if necessary
if z > z_max:
z_max = z
if z < z_min:
z_min = z
except MyWarning as e:
exit(f"Error on line {str(y)}, item {str(x)}: {e}")
return points, z_max, z_min

However

My problem is that:

1. I feel assign_points is too bloated and does/returns too much.
2. the input lists can get quite big and I think looping trough them more than once is wasteful
3. I'm not sure global vars is best practice

I thought about doing a function that stored the values and (depending on a flag as argument) returned the maximum values once called outside assign_points. But I'm pretty sure python doesn't have static vars (right?)

How would you go about this problem? Should I leave it as is or make global vars or do a 3rd option?

As suggested in the comments, defining your own class would allow you to instantiate and manipulate objects to your liking.

Since there seem to be three relevant values (points, z_max and z_min) you could let your class inherit from namedtuple. assign_points can then be created as a method of your class:

from collections import namedtuple

class Vec4Obj(namedtuple('Vec4Obj', ['points', 'z_max', 'z_min'])):
    def __new__(cls):
        return super().__new__(cls, [], float('-inf'), float('inf'))

    def assign_points(self, lists: list):
        for y, l in enumerate(lists):
            for x, point in enumerate(l):
                try:
                    z, color = parse_point(point)
                    if color is None:
                        color = no_color(z)
                    self.points.append(Vec4(x, y, z, 0, color))
                    
                    # Update z_max and z_min if necessary
                    if z > self.z_max:
                        self.z_max = z
                    if z < self.z_min:
                        self.z_min = z

                except Warning as e:
                    exit(f"Error on line {str(y)}, item {str(x)}: {e}")

You can define other methods. For instance one that would take only one list and a y value to avoid looping over all lists, hence adding fewer points at once.

Using your class would look like:

my_obj = Vec4Obj() # instantiate with value Vec4Obj(points=[], z_max=-inf, z_min=inf)

my_obj.assign_points(lists) # add points to my_obj.points and set my_obj.z_min and my_obj.z_max