Gooey GUIs ,tkinter ,Label Tricks, Let's Talk About Text Baby,It All Adds Up,Packing

 Gooey GUIs

DISCLAIMER: As the title states, this can get gooey. TKinter totally sucks - if you'd rather move on to something more fun, click "mark lesson as complete" and move on to Day 70 to get back to the good stuff.

It's time to bring our programs into the early 90s as we learn how to create a Graphical User Interface (GUI) with a Python library called tkinter.

 
tkinter

tkinter is one of the more popular Python GUI libraries.

👉 When you start a tkinter project, you get some boilerplate, or starter code. 

import tkinter as tk

window = tk.Tk()

window.title("Hello World") # Sets the name of the window in the border

window.geometry("300x300") # Sets the size of the window in pixels

hello = tk.Label(text = "Hello World") # Creates a text box

hello.pack() # 'pack' places the element on the screen

button = tk.Button(text = "Click me!") # Creates a button

button.pack()

tk.mainloop() 

This code will produce a window that looks like this:

Play around with the size of the window to see the effect of changing the dimensions.

Label Tricks

👉 We can also use variables to pass strings into labels like this:

label = "Hey there world"

hello = tk.Label(text = label) 

👉 Now I'm going to use a subroutine that changes the text in the label when I click the button.

window = tk.Tk()

window.title("Hello World") 

window.geometry("300x300") 

label = "Hey there world"

def updateLabel():

  label = "Bye world!"

  hello["text"] = label 

  # Subroutine that updates the text in the label.

hello = tk.Label(text = label) 

hello.pack() 

button = tk.Button(text = "Click me!", command = updateLabel) # Calls the updateLabel subroutine when the button is clicked

button.pack()

tk.mainloop() 

👉 Let's try the same trick, only this time the label contains a number which increments with every button click. For this I need to use a global label variable

.

window = tk.Tk()

window.title("Hello World") 

window.geometry("300x300") 

label = 0 # Sets the starting label value to 0

def updateLabel():

  global label # Uses the values in the label variable

  label += 1 # Adds one to the value in the label

  hello["text"] = label 

  

hello = tk.Label(text = label) 

hello.pack() 

button = tk.Button(text = "Click me!", command = updateLabel) # Calls the updateLabel subroutine when the button is clicked

button.pack()

tk.mainloop() 

Adding Text

Let's Talk About Text Baby

We can add text boxes to our windows using the entirely obvious text command.

👉 Here's the code you need in isolation: 

text = tk.Text(window ,height=1, width = 50)

# Three arguments, name of the window to place the text box in, height & width.

text.pack 

👉 And here it is in context. 

window = tk.Tk()

window.title("Hello World") 

window.geometry("300x300") 

label = 0

def updateLabel():

  global label

  label += 1 

  hello["text"] = label 

  

hello = tk.Label(text = label) 

hello.pack() 

button = tk.Button(text = "Click me!", command = updateLabel) 

button.pack()

text = tk.Text(window ,height=1, width = 50)

text.pack

tk.mainloop()

This gives us a window with a text box like this:

It All Adds Up

Let's make our program add the number in the text box to the number in the label when the button is pressed.

👉 To do this, we need to change the updateLabel subroutine. Here's the code in isolation:

def updateLabel():
  global label
  number = text.get("1.0","end") # Gets the number from the text box (starting at the first position and going to the end.) and stores in the number variable
  number = int(number) #Casts to an integer. I've done this on a separate line to prevent the line above getting too complex, but you can combine the two.
  label += number # Adds the number from the text box to the one in the label.
  hello["text"] = label 
Placing Items
Our window does look a bit odd, doesn't it? Why have the button above the text box?

👉 We can simply change the order by defining the text box before the button in

 the code: window = tk.Tk()
window.title("Hello World") 
window.geometry("300x300") 
label = 0
 def updateLabel(): 
  global label
  number = text.get("1.0","end") 
  number = int(number) 
  label += number
  hello["text"] = label 
  
hello = tk.Label(text = label) 
hello.pack() 
text = tk.Text(window ,height=1, width = 50)
text.pack
button = tk.Button(text = "Click me!", command = updateLabel) 
button.pack()
tk.mainloop() 

Packing

We can add arguments to pack() to control the position of items in the window. Again, I'm just showing the relevant lines of code in these examples.

👉 Let's move the button to the bottom of the window.
button.pack(side=tk.BOTTOM)

👉 And the text box to the top to the left of the window.

text.pack(side=tk.LEFT)
You can also use TOP, RIGHT, CENTER to control location.
Unpacking
If we had several buttons, the default would be to put them one on top of another.
button = tk.Button(text = "Click me!",
command = updateLabel) 
button.pack()
button = tk.Button(text = "Another Button", command = updateLabel) 
button.pack()
button = tk.Button(text = "Last one", command = updateLabel) 
button.pack()

We can arrange them into a nicer grid layout, but to do this we have to completely remove pack and break the entire window into a grid.

👉 We then use row and column numbers (zero indexed remember) to place our elements. I've put the label in row 0, text box in row 1 and buttons in row 2.

window = tk.Tk()
window.title("Hello World") 
window.geometry("300x300") 
label = 0
def updateLabel():
  global label
  number = text.get("1.0","end") 
  number = int(number) 
  label += number
  hello["text"] = label 
  
hello = tk.Label(text = label).grid(row=0, column=1)
text = tk.Text(window ,height=1, width = 50).grid(row=1, column=1)
button = tk.Button(text = "Click me!", command = updateLabel).grid(row=2, column=0)
button = tk.Button(text = "Another Button", command = updateLabel).grid(row=2, column=1)
button = tk.Button(text = "Last one", command = updateLabel).grid(row=2, column=2)
tk.mainloop()