Scope

When we create variables in any programming language, they are normally the concatenation of the variable and its namespace. We say that a variable has scope.

Run the following code with a nested function.

What results do you get and why?

my_string = "global"

def my_function():
    my_string = "enclosing"
    def nested_function():
        my_string = "local"
        print(my_string)
    nested_function()
    return my_string

# Print the variable my_string
print(my_string)
# Print the output of the function, my_function
print(my_function())

Python has a hierarchy with which it looks for variables as LEGB.

1. Local names assigned in a function and not declared as global

2. Enclosing function locals, names in an enclosing function where we next functions

3. Global names assigned at the top level of a Python module, or declared as global

4. Built in names in Python, do not override these!

Using the global keyword, I can change the global variable name from within a function.

my_string = "global"

def my_function():
    global my_string
    print(f"At the moment, my_string is: {my_string}")
    my_string = "mangled!"

my_function()
print(f"Now the global value of my_string is: {my_string}")

Avoid using the global keyword unless you have a very specific reason to. Its much less confusing to change a module level variable using the return value of a function.

Exercise 1

Briefly explain and comment this code.

What values in the final statement will result in the function returning True?

Why?

def divisible(numerator: int, denominator: int)->bool:
    return numerator % denominator == 0

print(divisible(30,4))

Exercise 2

Briefly explain and comment this code.

Why do you get the value None?

What values in the final statement will result in the function returning True?

Why?

Can you modify this function to return False instead of None if the value is not found?

def find_num(number_list: list, number: int)->bool:
    for iterate_number in number_list:
        if iterate_number == number:
            return True
        else:
            pass

result = find_num([1,2,3,4,5,6,7,8], 9)
print(result)

Exercise 3

Write a function to search for an even number in a list of numbers.

Return True if you find an even number.

Return False if you do not.

Write a lambda function to calculate the volume of a cylinder.