cs2370 Notes: 18 Scopes and Debuggers

First, let’s try to install the Mu editor.

What’s Mu?

An alternative to IDLE
Not installed by default with Python
Comes with a bunch of packages
The debugger does more of what I want today.

How do names work in Python? #

# global variable
color = "green"


def add1(xx):
    # xx is a parameter
    # yy is a local variable
    # parameters are just local variables that are created as
    # part of the function call process
    yy = xx + 1
    return yy
    
print(add1(5))

Globals are available in functions:

nn = 7

def add_nn(xx):
    return xx + nn
  
print(add_nn(3))

# >>> nn = 8
# >>> add_nn(3)

Assignment creates new local by default:

nn = 0

def set_nn_to_5():
    # global nn
    nn = 5
    print("new nn =", nn)

There are no block scopes:

def foo():
    if True:    # if False:
        x = 2
    
    print(x)

foo()

There are nested functions:

def nested_add1(xx):
    def add1():
        return xx + 1
    return add1()

Now let’s figure this example out:

def make_counter():
    count = 0
    
    def counter():
        nonlocal count
        count += 1
        return count

    return counter

aa = make_counter()
print(aa())
bb = make_counter()
print(aa())
print(bb())

So there are four scopes:

local
nonlocal
global
builtin - stuff like “print” that’s availble everywhere

In python there is only one kind of name. So all of:

variables containing normal data
functions
modules
classes (we’ll talk more about those later)

all share the same names

Functions to debug:

items = [[0, 1, 2, 3], 4, [5, 6, [7, 8]], 9]

def sum_nested(xs):
    sum = 0
    
    if type(xs) is list:
        for xx in xs:
            sum_nested(xs)
    else:
        return xs