How does defining a function nested in another work? - python-3.x

Question

In the Python implementation of the Xiaolin Wu's line algorithm, a function is defined while being nested in another function. Part of the code:
def draw_line(img, p1, p2, color):
"""Draws an anti-aliased line in img from p1 to p2 with the given color."""
x1, y1 = p1
x2, y2 = p2
dx, dy = x2-x1, y2-y1
steep = abs(dx) < abs(dy)
p = lambda px, py: ((px,py), (py,px))[steep]
if steep:
x1, y1, x2, y2, dx, dy = y1, x1, y2, x2, dy, dx
if x2 < x1:
x1, x2, y1, y2 = x2, x1, y2, y1
grad = dy/dx
intery = y1 + _rfpart(x1) * grad
def draw_endpoint(pt):
x, y = pt
xend = round(x)
yend = y + grad * (xend - x)
xgap = _rfpart(x + 0.5)
px, py = int(xend), int(yend)
putpixel(img, p(px, py), color, _rfpart(yend) * xgap)
putpixel(img, p(px, py+1), color, _fpart(yend) * xgap)
return px
How does this work? Why didn't the programmer just define the code somewhere else and then call it in this function? If this function where to be called in a loop to draw multiple lines, wouldn't it be more efficient to just, as I said, define the nested function somewhere else?

Answer 1

try this:
class Humans():
def health(self, weight, height, age):
self.weight = weight
self.height = height
self.age = age
def health_health(self):
print(f'''This human is {self.age} years old; weighs {self.weight},
and has a height of {self.height}''')
Harar = Humans()
Harar.health(1,2,3)
Harar.health_health()

Answer 2

The reason why is because you are calling the function from the class definition, as opposed to the initialized object. You can do two things to fix this:
Call the function from the object that has been initialized:
class Foo:
def bar(x):
print(x)
a = Foo()
a.bar(10)
Or, define the function as a staticmethod:
class Foo:
#staticmethod
def bar(x):
print(x)
Foo.bar(10)
Both will output:
10