Learn to Program 22
In this part of the Learn to Program series we make a working calculator from start to finish in one video. We create a Use Case Description to figure out exactly what must occur in the program step-by-step. We then create a calculator object, convert the use case into code, create the GUI interface using TkInter and end with homework you should solve to improve your programming abilities. Calculator PDF is Here.
All of the code, the use case and a cheat sheet for the video can be found after the video below. You should refer to it through out this video to help you learn the topics covered.
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Code & Cheat Sheet
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Use Case Description Describes Everything the App Does Step-By-Step I. User clicks a number button N3. With each number button press add the new value to the end of the first and update entry II. User clicks a math button N1. Make sure entry has a value N2. Switch boolean values representing math buttons to false on entry N2. Have Button pass in the math function pressed N4. Store the entry value on entry to this function (Class Field) N4. Clear the entry field? III. User clicks another number button IV. User clicks equal button and the result shows N1. Make sure a math function was clicked N2. Check which math function was clicked and provide the correct solution Note 1 : Since every button requires the previous button to have been clicked make sure the click occurred Note 2 : Make a way to track which math button was clicked last Note 3 : Think about a way to handle the user entering both single numbers and multiple numbers Note 4 : Track the first number in the entry box after a math button is clicked Note 5 : What about division problems caused by an integer division? a. Convert to float each time we retrieve, or store values in the entry from tkinter import * from tkinter import ttk class Calculator: # Stores the current value to display in the entry calc_value = 0.0 # Will define if this was the last math button clicked div_trigger = False mult_trigger = False add_trigger = False sub_trigger = False # Called anytime a number button is pressed def button_press(self, value): # Get the current value in the entry entry_val = self.number_entry.get() # Put the new value to the right of it # If it was 1 and 2 is pressed it is now 12 # Otherwise the new number goes on the left entry_val += value # Clear the entry box self.number_entry.delete(0, "end") # Insert the new value going from left to right self.number_entry.insert(0, entry_val) # Returns True or False if the string is a float def isfloat(self, str_val): try: # If the string isn't a float float() will throw a # ValueError float(str_val) # If there is a value you want to return use return return True except ValueError: return False # Handles logic when math buttons are pressed def math_button_press(self, value): # Only do anything if entry currently contains a number if self.isfloat(str(self.number_entry.get())): # make false to cancel out previous math button click self.add_trigger = False self.sub_trigger = False self.mult_trigger = False self.div_trigger = False # Get the value out of the entry box for the calculation self.calc_value = float(self.entry_value.get()) # Set the math button click so when equals is clicked # that function knows what calculation to use if value == "/": print("/ Pressed") self.div_trigger = True elif value == "*": print("* Pressed") self.mult_trigger = True elif value == "+": print("+ Pressed") self.add_trigger = True else: print("- Pressed") self.sub_trigger = True # Clear the entry box self.number_entry.delete(0, "end") # Performs a mathematical operation by taking the value before # the math button is clicked and the current value. Then perform # the right calculation by checking what math button was clicked # last def equal_button_press(self): # Make sure a math button was clicked if self.add_trigger or self.sub_trigger or self.mult_trigger or self.div_trigger: if self.add_trigger: solution = self.calc_value + float(self.entry_value.get()) elif self.sub_trigger: solution = self.calc_value - float(self.entry_value.get()) elif self.mult_trigger: solution = self.calc_value * float(self.entry_value.get()) else: solution = self.calc_value / float(self.entry_value.get()) print(self.calc_value, " ", float(self.entry_value.get()), " ", solution) # Clear the entry box self.number_entry.delete(0, "end") self.number_entry.insert(0, solution) def __init__(self, root): # Will hold the changing value stored in the entry self.entry_value = StringVar(root, value="") # Define title for the app root.title("Calculator") # Defines the width and height of the window root.geometry("430x220") # Block resizing of Window root.resizable(width=False, height=False) # Customize the styling for the buttons and entry style = ttk.Style() style.configure("TButton", font="Serif 15", padding=10) style.configure("TEntry", font="Serif 18", padding=10) # Create the text entry box self.number_entry = ttk.Entry(root, textvariable=self.entry_value, width=50) self.number_entry.grid(row=0, columnspan=4) # ----- 1st Row ----- self.button7 = ttk.Button(root, text="7", command=lambda: self.button_press('7')).grid(row=1, column=0) self.button8 = ttk.Button(root, text="8", command=lambda: self.button_press('8')).grid(row=1, column=1) self.button9 = ttk.Button(root, text="9", command=lambda: self.button_press('9')).grid(row=1, column=2) self.button_div = ttk.Button(root, text="/", command=lambda: self.math_button_press('/')).grid(row=1, column=3) # ----- 2nd Row ----- self.button4 = ttk.Button(root, text="4", command=lambda: self.button_press('4')).grid(row=2, column=0) self.button5 = ttk.Button(root, text="5", command=lambda: self.button_press('5')).grid(row=2, column=1) self.button6 = ttk.Button(root, text="6", command=lambda: self.button_press('6')).grid(row=2, column=2) self.button_mult = ttk.Button(root, text="*", command=lambda: self.math_button_press('*')).grid(row=2, column=3) # ----- 3rd Row ----- self.button1 = ttk.Button(root, text="1", command=lambda: self.button_press('1')).grid(row=3, column=0) self.button2 = ttk.Button(root, text="2", command=lambda: self.button_press('2')).grid(row=3, column=1) self.button3 = ttk.Button(root, text="3", command=lambda: self.button_press('3')).grid(row=3, column=2) self.button_add = ttk.Button(root, text="+", command=lambda: self.math_button_press('+')).grid(row=3, column=3) # ----- 4th Row ----- self.button_clear = ttk.Button(root, text="AC", command=lambda: self.button_press('AC')).grid(row=4, column=0) self.button0 = ttk.Button(root, text="0", command=lambda: self.button_press('0')).grid(row=4, column=1) self.button_equal = ttk.Button(root, text="=", command=lambda: self.equal_button_press()).grid(row=4, column=2) self.button_sub = ttk.Button(root, text="-", command=lambda: self.math_button_press('-')).grid(row=4, column=3) # Get the root window object root = Tk() # Create the calculator calc = Calculator(root) # Run the app until exited root.mainloop() |
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