Finishing the Firework Demo

Return of the Firework

from pgl import GWindow, GOval, GRect
import random

GW_WIDTH = 500
GW_HEIGHT = 500

def random_color():
    color = "#"
    for _ in range(6):
        color += random.choice("0123456789ABCDEF")
    return color

class Firework:
    """ Creates a new firework with initial flight and then 
    explosion. 
    """
    def __init__(self, size):
        self.obj = GOval(GW_WIDTH/2, GW_HEIGHT, size, size)
        self.obj.set_filled(True)
        self.obj.set_color("white")
        self.speed = 5
        self.heading = random.randint(60,120)
        self.fuse = random.randint(50,100)
        self.maxsize = random.randint(60,100)
        self.color = random_color()
        self.mode = 0

    def get_object(self):
        """ Returns the firework graphical object. """
        return self.obj

    def should_terminate(self):
        """ Checks if the firework should be removed. """
        return self.mode > 1

    def move(self):
        """ Moves the firework in its initial flight. """
        self.obj.move_polar(self.speed, self.heading)
        self.fuse -= 1
        if self.fuse < 0:
            self.mode += 1
            self.obj.set_color(self.color)

    def explode(self):
        """ Grows the firework explosion upon detonation. """
        R = 2
        x = self.obj.get_x()
        y = self.obj.get_y()
        S = self.obj.get_width()
        self.obj.set_bounds(x-R/2, y-R/2, S+R, S+R)
        if self.obj.get_width() >= self.maxsize:
            self.mode += 1

    def update(self):
        """ Controls what the firework should be doing during 
        each stage. 
        """
        if self.mode == 0:
            self.move()
        elif self.mode == 1:
            self.explode()
       

def fireworks_show():
    """ Makes a fireworks show! """
    def step():
        """ Calls up update method on all fireworks in the box 
        and removes if necessary.
        """
        for f in firework_box[:]:
            f.update()
            if f.should_terminate():
                gw.remove(f.get_object())
                firework_box.remove(f)


    def give_me_more_fireworks():
        """ Adds more fireworks to the box. """
        new = Firework(2)
        firework_box.append(new)
        gw.add(new.get_object())

    gw = GWindow(GW_WIDTH, GW_HEIGHT)
    sky = GRect(GW_WIDTH, GW_HEIGHT)
    sky.set_filled(True)
    gw.add(sky)
    firework_box = []

    gw.set_interval(step, 20)
    gw.set_interval(give_me_more_fireworks, 100)

if __name__ == '__main__':
    fireworks_show()

Maps and Dictionaries

• A common form of information associates pairs of data values
  • Commonly called a map in computer science
  • Python calls such a structure a dictionary
• A dictionary associates two different values:
  • A simple value called the key, which is often a string but doesn’t need to be
  • A larger and more complex object called the value
• This idea of associating pairs of values is exhibited all over in the real world
  • Actual dictionaries! The words are the keys, the definitions the values.
  • Web addresses! Keys are the urls, the values are the webpage contents.

Creating Dictionaries

• Python dictionaries use squiggly brackets or braces {} to enclose their contents

• Can create an empty dictionary by providing no key-value pairs:

  empty_dict = {}

• If creating a dictionary with key-value pairs

  • Keys are separated from values with a colon :
  • Pairs are separated by a comma ,

  generic_dict = {'Bob': 21, 0: False, 13: 'Thirteen'}

Keys and Values

• The value of a key-value pair can be any Python object, mutable or immutable
  • This include other dictionaries!
• The key is more restricted:
  • Must be immutable
    • So dictionaries or lists can not work as a key
    • Tuples can though!
  • Must be unique per dictionary

A = {True: 'Seth', False: 'Jesse'}
B = {'Jill': 13, 'Jack': 12}
C = {(1,2): {'x': 1}}

X = {{'x': 1, 'y': 2}: 'Shark'}
Y = {[1,3,5]: 'Odd'}
Z = {'A': 13, 'B': 24, 'A': 15}

Selection

• The fundamental operation on dictionaries is selection, which is still indicated with square brackets: []

• Dictionaries though are unordered, so it is not a numeric index that goes inside the [ ]

• You instead use the key directly to select corresponding values:

  >>> A = {'Jack': 12, 'Jill': 13}['Jack']
  >>> print(A)
  12
  >>> B = {True: 13, 0: 'Why?'}[0]
  >>> print(B)
  Why?

Losing your keys

• If you attempt to index out a key that doesn’t exist:

  A = {'Jack': 12, 'Jill': 13}
  print(A['Jil'])

  you will get an error!

• If in doubt, check for the presence of a key with the in operator:

  if 'Jil' in A:
      print(A['Jil'])

Rewriting the Dictionary

• Dictionaries are mutable!
  • We can add new key-value pairs
  • We can change the value of corresponding keys

  >>> d = {}
  >>> d['A'] = 10
  >>> d['B'] = 12
  >>> print(d)
  {'A':10, 'B':12}
  >>> d['A'] = d['B']
  >>> print(d)
  {'A':12, 'B':12}

Understanding Check

What is the printed value of the below code?

A = [
    {'name': 'Jill',  'weight':125, 'height':62},
    {'name': 'Sam',   'height':68},
    {'name': 'Bobby', 'height':72},
]
A.append({'weight':204, 'height':70, 'name':'Jim'})
B= A[1]
B['weight'] = 167
print([d['weight'] for d in A if 'weight' in d])

Iterating through a Dictionary

• Frequently we might want to iterate through a dictionary, checking either its values or its keys

• Python supports iteration with the for statement, which has the form of:

  for key in |||dictionary|||:
      value = |||dictionary|||[key]
      |||code to work with that key and value|||

• You can also use the .items method to grab both key and values together:

  • Returns a tuple with both the key and corresponding pair

  for key, value in |||dictionary|||.items():
      |||code to work with that key and value|||

Finding Students by grade

• Suppose we had a file of student ids and corresponding grades on a test

• We want a simple program where we can enter in a target grade and have it tell us all the students who received that grade

  def read_to_dict(filename):
      dictionary = {}
      with open(filename) as f:
        for line in f:
            ID, score = line.strip().split(',')
            dictionary[ID] = score
      return dictionary
  
  def get_students_with_score():
      scores = read_to_dict('SampleGrades.txt')
      done = False
      while not done:
          des_grade = input('Enter a letter grade: ')
          if des_grade == "":
              done = True
          else:
              for st_id, grade in scores.items():
                  if grade == des_grade.strip().upper():
                      print(f"{st_id} got a {grade}")

Common Dictionary Methods

Dictionary Records

• While most commonly used to indicate mappings, dictionaries have seen increased use of late as structures to store records

• Looks surprisingly close to our original template of:

  boss = {
      'name': 'Scrooge',
      'title': 'founder',
      'salary': 1000
      }

• Allows easy access of attributes without worrying about ordering

  print(boss['name'])

• It is still using a mutable data-type to represent something that should be immutable though

Mathematical Sets

• A set is an unordered collection of distinct values.
  • digits = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
  • evens = 0, 2, 4, 6, 8
  • odds = 1, 3, 5, 7, 9
  • primes = 2, 3, 5, 7
  • squares = 0, 1, 4, 9
  • primary = red, green, blue
  • \(\mathbf{R}\) = x where x is a real number
  • \(\mathbf{Z}\) = x where x is an integer
  • \(\mathbf{N}\) = x where x is an integer >=0
• The set with no elements is call the empty set (∅)

Pythonic Sets

• Enclosed within squiggly brackets
• No key-value pairs, just single values separated by commas

digits = { 0, 1, 2, 3, 4, 6, 7, 8, 9 }
squares = { 0, 1, 4, 9 }
primary = { "red", "green", "blue" }

• Set elements must be immutable
• Sets themselves are generally mutable
• Can not create an empty set just using { }!
  • Python assumes this to be an empty dictionary!
  • Must instead use set().

Set Operations

• The fundamental set operation is membership (∈)
  • 3 ∈ primes
  • 3 ∉ evens
  • red ∈ primary
  • -1 ∉ N
• The union of the sets \(A\) and \(B\) (\(A \cup B\)) consists of all elements in either \(A\) or \(B\) or both.
• The intersection of the sets \(A\) and \(B\) (\(A \cap B\)) consists of all elements in both \(A\) and \(B\).
• The set difference of \(A\) and \(B\) (\(A - B\)) consists of all elements in \(A\) but not in \(B\).
• The symmetric set difference of \(A\) and \(B\) (\(A\triangle B\)) consists of all elements in \(A\) or \(B\) but not in both.

Python Implementations

• Python’s built-in implementation of sets supports all these same operations
• Can either use appropriately named methods on sets or operators between sets
• Membership 3 in primes

Venn Diagrams

• A Venn Diagram is a graphical representation of a set which indicates common elements as overlapping areas
• The following Venn diagrams illustrate the effect of the 4 primary set operations