Scoping Functions

Announcements

• Project Wordle is due today at 10 pm.
• Grading for PS3 will be returned this week! Apologies for the delay
• We are in Ch6 of the text this week, which is interactive graphics
• Remember the 1st midterm exam is this Friday Feb 23 in this hall
  • I will provide more information about the exam right this morning
  • Those with accommodations with Testing Center should contact them to make arrangement NOW! and cc me in the email
• Polling continues https://www.polleverywhere.com/agbofred203

Mystery word

• Let us walk through this program and unravel what will be printed when the program complete execution.

def mystery (x):
    def enigma (s, t):
        t -= 2
        return s [::6] + s[t]
    y = len(x)
    z = x[1 - y]
    z += enigma (x, y)
    z += enigma (x, y - 2)
    return z

if __name__ == '__main__':
    print(mystery ("abcdefgh"))

Graphic function with default color

• You can return any type of variable from a function, including GObject graphical objects
• Can be useful to write simple functions that bundle together common tasks
  • For instance, to create a filled circle centered at some location:

def make_filled_circ(x_cent, y_cent, radius, color='black'):
    circle = GOval(x_cent-radius, y_cent-radius, 2*radius, 2*radius)
    circle.set_color(color)
    circle.set_filled(True)
    return circle

Summary of a Function Call

Name Resolution and Scope

• When Python encounters a variable name in a program, it looks for where the variable was defined in an expanding search:
  1. Local - The local context is all the variables defined within the current function. This includes variables appearing as a parameter!
  2. Enclosing - The enclosing context consists of the names defined in a function enclosing the current one.
  3. Global - The global context consists of names defined outside of any function or imported into the current module.
  4. Built-in - The last place Python looks is in the names of any built-in functions, like abs, str, print, etc.
• The part of a program in which a name is defined in called its scope

Scoping Example

def func1(x,y):
    return z + func2(x,y)
 
def func2(x,y):
    def func3(x):
        return (y + x) ** 2
 
    z = x - func3(y)
    return z - y
 
z = 1
print(func1(2,z))

Local Variables

• In Python, assigning any value to a variable means that the variable is assumed to be local

  • This generally makes sense, as you would not want more specific functions overriding variables in other areas

• Can lead to issues though:

  def increment():
    x = x + 1
  
  x = 0
  increment()

• The variable x in the fuction is local within that scope, and another global x with value 0 can cause issues

Review Question!

def f(x,y=0):
    z = (x + 3) ** 2
    return y + z

x = 1
z = x + f(y=x,x=2)
print(z)

The Python Event Model

• Graphical applications usually make it possible for the user to control the action of a program by using an input device such a mouse.
  • Programs supporting this type of control are called interactive programs.
• User actions such as clicking the mouse are called events.
• Programs that respond to events are said to be event driven.
• User input does not generally occur at predictable times. As the events are not controlled by the program, they are said to be asynchronous.
• In Python, you write a function that acts as a listener for a particular event type. When the event happens, the listener is called.

First Class Functions

• Functions in Python are treated as data values just like anything else!
  • We will need to take advantage of this to write listener functions.
• You can assign a function to a variable, pass it as a parameter, return it as a result, etc
• Functions treated like any other data value are called first-class functions
• To work with a function itself, you leave off the (). Including the parentheses is how you call the function!

A First Class Example

import math

def evaluate_numbers(func):
    print(func)
    print(func(0))
    print(func(2))
    print(func(10))

A = evaluate_numbers

A(math.sqrt)
A(math.exp)

Closures

b = 1
def f1(a):
    print(a)
    print(b)
 
    def f2():
        c = a + b
        return c * 3
    return f2 
 
f2 = f1(10) 
c = f2()

Mid-term test

• Test will take place during the class time 0n Friday.
• Those with accommodations should already contact the testing center and cc me.
• Practice questions are posted on this week’s module
• Basic things to keep in mind:
  • The test contain detailed information to guide on what to expect. Read it carefully
  • The exam is partially open, and thus you are free to utilize:
    • The text
    • Your notes
    • Class slides
    • Any past work you have done as part of sections, problem sets, or projects, provided it has been uploaded, and you access it through GitHub.

Mid-term test

• You are allowed to use a computer for ease of typing and accessing the above resources,
• You are prohibited from accessing and using any editor or terminal to run your code.
  • Visual Studio Code or any similar editor should never be open on your computer during this exam.
• Additionally, you are prohibited from accessing outside internet resources beyond the webpages described above.
• practice questions (2 at least) will be posted today and Wednesday
  • first practice questions would be sent in PDF
  • second practice questions would be on canvas