In this chapter, we start creating amazing GUIs using Python 3.6 and above. We will cover the following topics:
- Creating our first Python GUI
- Preventing the GUI from being resized
- Adding a label to the GUI form
- Creating buttons and changing their text property
- Text box widgets
- Setting the focus to a widget and disabling widgets
- Combo box widgets
- Creating a check button with different initial states
- Using radio button widgets
- Using scrolled text widgets
- Adding several widgets in a loop
In this chapter, we will develop our first GUI in Python. We will start with the minimum code required to build a running GUI application. Each recipe then adds different widgets to the GUI form.
In the first two recipes, we will show the entire code, consisting of only a few lines of code. In the following recipes, we will only show the code to be added to the previous recipes.
By the end of this chapter, we will have created a working GUI application that consists of labels, buttons, text boxes, combo boxes, check buttons in various states, as well as radio buttons that change the background color of the GUI.
At the beginning of each chapter, I will show the Python modules that belong to each chapter. I will then reference the different modules that belong to the code shown, studied and run.
Here is the overview of Python modules (ending in a .py extension) for this chapter:
Python is a very powerful programming language. It ships with the built-in
tkinter module. In only a few lines of code (four, to be precise) we can build our first Python GUI.
To follow this recipe, a working Python development environment is a prerequisite. The IDLE GUI, whichÂ ships with Python, is enough to start. IDLE was built using tkinter!
- All the recipes in this book were developed using Python 3.6 on a Windows 10 64-bit OS. They have not been tested on any other configuration. As Python is a cross-platform language, the code from each recipe is expected to run everywhere.
- If you are using a Mac, it does come with built-in Python, yet it might be missing some modules such as tkinter, which we will use throughout this book.
- We are using Python 3.6, and the creator of Python intentionally chose not to make it backwards compatible with Python 2. If you are using a Mac or Python 2, you might have to install Python 3.6 from www.python.org in order to successfully run the recipes in this book.
- If you really wish to run the code in this book on Python 2.7, you will have to make some adjustments. For example, tkinter in Python 2.x has an uppercase T. The Python 2.7Â print statement is a function in Python 3.6 and requires parentheses.
- While the EOL (End Of Life) for the Python 2.x branch has been extended to the year 2020, I would strongly recommend that you start using Python 3.6 and above.
- Why hold on to the past, unless you really have to? Here is a link to the Python Enhancement Proposal (PEP) 373 that refers to the EOL of Python 2:Â https://www.python.org/dev/peps/pep-0373/
Here are the four lines of
First_GUI.py required to create the resulting GUI:
Execute this code and admire the result:
In line nine, we import the built-in
tkinter module and alias it as
tk to simplify our Python code. In line 12, we create an instance of the
Tk class by calling its constructor (the parentheses appended to
Tk turns the class into an instance). We are using the alias
tk, so we don't have to use the longer word
tkinter. We are assigning the class instance to a variable named
win (short for a window). As Python is a dynamically typed language, we did not have to declare this variable before assigning to it, and we did not have to give it a specific type. Python infers the type from the assignment of this statement. Python is a strongly typed language, so every variable always has a type. We just don't have to specify its type beforehand like in other languages. This makes Python a very powerful and productive language to program in.
A little note about classes and types:
- In Python, every variable always has a type. We cannot create a variable that does not haveÂ a type. Yet, in Python, we do not have to declare the type beforehand, as we have to do in the C programming language.
- Python is smart enough to infer the type. C#, at the time of writing this book, also has this capability. Using Python, we can create our own classes using the
classkeyword instead of the
- In order to assign the class to a variable, we first have to create an instance of our class. We create the instance and assign this instance to our variable, for example:
Â Â print('Hello from AClass')Â class_instance = AClass()Now, the variable,Â
class_instance, is of theÂ
AClassÂ type. If this sounds confusing, do not worry. We will cover OOP in the coming chapters.
In line 15, we use the instance variable (
win) of the classÂ to give our window a title via the
title property. In line 20, we start the window's event loop by calling the
mainloop method on the class instance,Â
win. Up to this point in our code, we created an instance and set one property,Â but the GUI will not be displayed until we start the main event loop.
- An event loop is a mechanism that makes our GUI work. We can think of it as an endless loop where our GUI is waiting for events to be sent to it. A button click creates an event within our GUI, or our GUI being resized also creates an event.
- We can write all of our GUI code in advance and nothing will be displayed on the user's screen until we call this endless loop (
win.mainloop()in the preceding code). The event loop ends when the user clicks the red
Xbutton or a widget that we have programmed to end our GUI. When the event loop ends, our GUI also ends.
By default, a GUI created using tkinter can be resized. This is not always ideal. The widgets we place onto our GUI forms might end up being resized in an improper way, so in this recipe, we will learn how to prevent our GUI from being resized by the user of our GUI application.
This recipe extends the previous one,Â Creating our first Python GUI, so oneÂ requirement is to have typed the firstÂ recipe yourself into a project of your own, or download the code from https://github.com/PacktPublishing/Python-GUI-Programming-Cookbook-Second-Edition/.
We are preventing the GUI from being resized, look at:
Running the code creates this GUI:
Line 18 prevents the Python GUI from being resized.
Running this code will result in a GUI similar to the one we created in the first recipe. However, the user can no longer resize it. Also, note how the maximize button in the toolbar of the window is grayed out.
Why is this important? Because once we add widgets to our form, resizing can make our GUI look not as good as we want it to be. We will add widgets to our GUI in the next recipes.
resizable() method is of the
Tk() class, and by passing in
(False, False), we prevent the GUI from being resized.Â We can disable both the x and y dimensions of the GUI from being resized, or we can enable one or both dimensions by passing in
True or any number other than zero.Â
(True, False) would enable the x-dimension but prevent the y-dimension from being resized.
We also added comments to our code in preparation for the recipes contained in this book.
A label is a very simple widget that adds value to our GUI. It explains the purpose of the other widgets, providing additional information. This can guide the user to the meaning of an Entry widget, and it can also explain the data displayed by widgets without the user having to enter data into it.
We are extending the first recipe,Â Creating our first Python GUI. We will leave the GUI resizable, so don't use the code from the second recipe (or comment the
win.resizableÂ line out).
In order to add a
Label widget to our GUI, we will import the
ttk module from
tkinter. Please note the two import statements.Â Add the following code just above
win.mainloop(), which is located at the bottom of the first and second recipes:
Running the code adds a label to our GUI:
In line 10 of the precedingÂ code, we import a separate module from theÂ
tkinterÂ package. The
ttk module has some advanced widgets that make our GUI look great. In a sense,
ttk is an extension within theÂ
We still need to import theÂ
tkinter package itself, but we have to specify that we now want to also use
ttk from theÂ
Line 19 adds the label to the GUI, just before we call
We pass our window instance into the
ttk.Label constructor and set the text property. This becomes the text our
Label will display.
We also make use of the grid layout manager, which we'll explore in much more depth in Chapter 2, Layout Management.
Note how our GUI suddenly got much smaller than in the previous recipes.
The reason why it became so small is that we added a widget to our form. Without a widget, theÂ
tkinterÂ package uses a default size. Adding a widget causes optimization, which generally means using as little space as necessary to display the widget(s).
If we make the text of the label longer, the GUI will expand automatically. We will cover this automatic form size adjustment in a later recipe in Chapter 2, Layout Management.
In this recipe, we will add a button widget, and we will use this button to change a property of another widget that is a part of our GUI. This introduces us to callback functions and event handling in a Python GUI environment.
This recipe extends the previous one, Adding a label to the GUI form. You can download the entire code from https://github.com/PacktPublishing/Python-GUI-Programming-Cookbook-Second-Edition/.
We add a button that, when clicked, performs an action. In this recipe, we will update the label we added in the previous recipe as well as the text property of the button:
The following screenshot shows how our GUIÂ looks before clicking the button:
After clicking the button, the color of the label changed and so didÂ the text of the button, which can be seen as follows:
In line 19, we assign the label to a variable, and in line 20, we use this variable to position the label within the form. We need this variable in order to change its properties in the
click_me() function. By default, this is a module-level variable, so we can access it inside the function, as long as we declare the variable above the function that calls it.
Line 23 is the event handler that is invoked once the button gets clicked.
In line 29, we create the button and bind the command to the
GUIs are event-driven. Clicking the button creates an event. We bind what happens when this event occurs in the callback function using the command property of the
ttk.Button widget. Notice how we do not use parentheses, only the nameÂ
We also change the text of the label to include
redÂ as, in the printed book, this might otherwise not be obvious. When you run the code, you can see that the color does indeed change.
Lines 20 and 30Â both use the grid layout manager, which will be discussed in the following chapter. This aligns both the label and the button.
In tkinter, the typical one-line textbox widget is called Entry. In this recipe, we will add such an Entry widget to our GUI. We will make our label more useful by describing what the Entry widget is doing for the user.
Check out the following code:
Now, our GUI looks like this:
After entering some text and clicking the button, there is the following change in the GUI:
In line 24, we get the value of the Entry widget. We haveÂ not used OOP yet, so how come we can access the value of a variable that was not even declared yet?
Without using OOP classes, in Python procedural coding, we have to physically place a name above a statement that tries to use that name. So how come this works (it does)?
The answer is that the button click event is a callback function, and by the time the button is clicked by a user, the variables referenced in this function are known and do exist.
Life is good.
Line 27 gives our label a more meaningful name;Â for now, it describes the text box below it. We moved the button down next to the label to visually associate the two. We are still using the grid layout manager, which willÂ be explained in more detail in Chapter 2, Layout Management.
Line 30 creates a variable,Â
name. This variable is bound to the Entry widget and, in our
click_me() function, we are able to retrieve the value of the Entry widgetÂ by calling
get() on this variable. This works like a charm.
Now we see that while the button displays the entire text we entered (and more), the textbox Entry widget did not expand. The reason for this is that we hardcoded it to a width of 12 in line 31.
- Python is a dynamically typed language and infers the type from the assignment. What this means is that if we assign a string to theÂ
nameÂ variable, itÂ will be of theÂ
stringtype, and if we assign an integer to
name, itsÂ type will be integer.
tkinter, we have to declare theÂ
namevariable as the type
tk.StringVar()before we can use it successfully. The reason is that tkinter is not Python. We can use it from Python, but it is not the same language.
While our GUI is nicely improving, it would be more convenient and useful to have the cursor appear in the Entry widget as soon as the GUI appears. Here we learn how to do this.
Python is truly great. All we have to do to set the focus to a specific control when the GUI appears is call the
focus() method on an instance of a
tkinter widget we previously created. In our current GUI example, we assigned the
ttk.Entry class instance to a variable named,Â
name_entered. Now, we can give it the focus.
Place the following code just above the code which is located at the bottom of the module and which starts the main windows event loop, like we did in the previous recipes:
If you get some errors, make sure you are placing calls to variables below the code where they are declared. We are not using OOP as of yet, so this is still necessary. Later, it will no longer be necessary to do this.
On a Mac, you might have to set the focus to the GUI window first before being able to set the focus to the Entry widget in this window.
Adding this one line (38) of Python code places the cursor in our text Entry widget, giving the text Entry widget the focus. As soon as the GUI appears, we can type into this text box without having to click it first.
We can also disable widgets. To do that, we will set a property on the widget. We can make the button disabled by adding this one line (37 below) of Python code toÂ createÂ the button:
After adding the precedingÂ line of Python code, clicking the button no longer creates any action:
This code is self-explanatory. We set the focus to one control and disable another widget. Good naming in programming languages helps to eliminate lengthy explanations. Later in this book, there will be some advanced tips on how to do this while programming at work or practicing our programming skills at home.
In this recipe, we will improve our GUI by adding drop-down combo boxes whichÂ can have initial default values. While we can restrict the user to only certain choices, we can also allow the user to type in whatever they wish.
This recipe extends the previous recipe, Setting the focus to a widget and disabling widgets.
We insert another column between the Entry widget and the
ButtonÂ widget using the grid layout manager. Here isÂ the Python code:
This code, when added to the previous recipes, creates the following GUI. Note how, in line 43 in the precedingÂ code, we assigned a tuple with default values to the combo box. These values then appear in the drop-down box. We can also change them if we like (by typing in different values when the application is running):
Line 40 adds a second label to match the newly created combo box (created in line 42). Line 41 assigns the value of the box to a variable of a special tkinter type
StringVar, as we did in a previous recipe.
Line 44 aligns the two new controls (label and combobox) within our previous GUI layout, and line 45 assigns a default value to be displayed when the GUI first becomes visible. This is the first value of the
number_chosen['values'] tuple, the string
"1". We did not place quotes around our tuple of integers in line 43, but they got casted into strings because, in line 41, we declared the values to be of theÂ
The preceding screenshot shows the selection made by the user asÂ
42. This value gets assigned to the
If we want to restrict the user to only be able to select the values we have programmed into the
Combobox, we can do that by passing the
state property into the constructor. Modify line 42 as follows:
Now, users can no longer type values into the
Combobox. We can display the value chosen by the user by adding the following line of code to our Button Click Event Callback function:
After choosing a number, entering a name, and then clicking the button, we get the following GUI result, which now also displays the number selected:
In this recipe, we will add three check button widgets, each with a different initial state.
We are creating three check button widgets that differ in their states. The first is disabled and has a check mark in it. The user cannot remove this check mark as the widget is disabled.
The second check button is enabled, and by default, has no check mark in it, but the user can click it to add a check mark.
The third check button is both enabled and checked by default. The users can uncheck and recheck the widget as often as they like. Look at the following code:
Running the new code results in the following GUI:
In lines 47, 52, and 57 we create three variables of theÂ
IntVar type. In the line followingÂ each of these variables, we create a
Checkbutton, passing in these variables. They will hold the state of the
Checkbutton (unchecked or checked). By default, that is either 0 (unchecked) or 1 (checked), so the type of the variable is a
We place these
Checkbutton widgets in our main window, so the first argument passed into the constructor is the parent of the widget, in our case,Â
win. We give each
CheckbuttonÂ widget a different label via its
Setting the sticky property of the grid to
tk.W means that the widget will be aligned to the west of the grid. This is very similar to Java syntax and it means that it will be aligned to the left. When we resize our GUI, the widget will remain on the left side and not be moved towards the center of the GUI.
Lines 49 and 59 place a checkmark into the
Checkbutton widget by calling the
select() method on these two
Checkbutton class instances.
We continue to arrange our widgets using the grid layout manager, which will be explained in more detail in Chapter 2, Layout Management.
In this recipe, we will create three tkinter
Radiobutton widgets. We will also add some code that changes the color of the main form, depending upon which
Radiobutton is selected.
This recipe extends the previous recipe, Creating a check button with different initial states.
We add the following code to the previous recipe:
Running this code and selecting the
Gold creates the following window:
In lines 75-77, we create some module-level global variables which we will use in the creation of each radio button as well as in the callback function that creates the action of changing the background color of the main form (using the instance variable
We are using global variables to make it easier to change the code. By assigning the name of the color to a variable and using this variable in several places, we can easily experiment with different colors. Instead of doing a global search-and-replace of a hardcoded string (which is prone to errors), we just need to change one line of code and everything else will work. This is known as the DRY principle, which stands for Don't Repeat Yourself. This is an OOP concept which we will use in the later recipes of the book.
The names of the colors we are assigning to the variables (
COLOR2 ...) are
tkinter keywords (technically, they are symbolic names). If we use names that are not
tkinter color keywords, then the code will not work.
Line 80 is the callback function that changes the background of our main form (
win) depending upon the user's selection.
In line 87 we create a
tk.IntVar variable. What is important about this is that we create only one variable to be used by all three radio buttons. As can be seen from the screenshot, no matter which
Radiobutton we select, all the others will automatically be unselected for us.
Lines 89 to 96 create the three radio buttons, assigning them to the main form, passing in the variable to be used in the callback function that creates the action of changing the background of our main window.
Here is a small sample of the available symbolic color names that you can look up at the official tcl manual page atÂ http://www.tcl.tk/man/tcl8.5/TkCmd/colors.htm.
Some of the names create the same color, so
alice blue creates the same color as
AliceBlue. In this recipe, we used the symbolic names
ScrolledText widgets are much larger than simple
Entry widgets and span multiple lines. They are widgets like Notepad and wrap lines, automatically enabling vertical scrollbars when the text gets larger than the height of the
This recipe extends the previous recipe, Using radio button widgets. You can download the code for each chapter of this book from https://github.com/PacktPublishing/Python-GUI-Programming-Cookbook-Second-Edition/.
By adding the following lines of code, we create a
We can actually type into our widget, and if we type enough words, the lines will automatically wrap around:
Once we type in more words than the height the widget can display, the vertical scrollbar becomes enabled. This all works out-of-the-box without us needing to write any more code to achieve this:
In line 11, we import the module that contains the
ScrolledText widget class. Add thisÂ to the top of the module, just below the other two
Lines 100 and 101 define the width and height of the
ScrolledText widget we are about to create. These are hardcoded values we are passing into the
ScrolledText widget constructor in line 102.
These values are magic numbers found by experimentation to work well. You might experiment by changing
scol_wÂ from 30 to 50 and observe the effect!
In line 102, we are also Â setting a property on the widget by passing in
By setting the
wrap property to
tk.WORD we are telling the
ScrolledText widget to break lines by words so that we do not wrap around within a word. The default option is
tk.CHAR, which wraps any character regardless of whether we are in the middle of a word.
The second screenshot shows that the vertical scrollbar moved down because we are reading a longer text that does not entirely fit into the x, y dimensions of the
SrolledText control we created.
columnspan property of the grid widget to
3 for the
SrolledText widget makes this widget span all the three columns. If we doÂ not set this property, our
SrolledText widget would only reside in column one, which is not what we want.
So far, we have created several widgets of the same type (for example,Â
Radiobutton) by basically copying and pasting the same code and then modifying the variations (for example, the column number). In this recipe, we start refactoring our code to make it less redundant.
We are refactoring some parts of the previous recipe's code, Using scrolled text widgets, so you need that code to apply this recipe to.
Here's how we refactor our code:
Running this code will create the same window as before, but our code is much cleaner and easier to maintain. This will help us when we expand our GUI in the comingÂ recipes.
In line 77, we have turned our global variables into a list.
In line 89, we set a default value to the
tk.IntVar variable that we named
radVar. This is important because, while in the previous recipe we had set the value for
Radiobutton widgets starting at 1, in our new loop it is much more convenient to use Python's zero-based indexing. If we did not set the default value to a value outside the range of our
Radiobutton widgets, one of the radio buttons would be selected when the GUI appears. While this in itself might not be so bad, it would not trigger the callback and we would end up with a radio button selected that does not do its job (that is, change the color of the main win form).
In line 95, we replace the three previously hardcoded creations of the
Radiobutton widgets with a loop thatÂ does the same. It is just more concise (fewer lines of code) and much more maintainable. For example, if we want to create 100 instead of just threeÂ
Radiobutton widgets, all we have to change is the number inside Python's range operator. We would not have to type or copy and paste 97 sections of duplicate code, just one number.
Line 82 shows the modified callback function.