Text stringlengths 1 9.41k |
|---|
The next two digits specify the green component (here 02, which is 2 in decimal), and the last two digits specify the blue component (here FF,
which is 255 in decimal). |
This color turns out to be a bluish violet. |
Here is an example of it in use:
label = Label(text='Hi', bg='#A202FF')
If you would rather not bother with hexadecimal, you can use the following function which will
convert percentages into the hex string that Tkinter uses.
**def color_convert(r, g, b):**
**return '#{:02x}{:02x}{:02x}'.format(int(r*2.55),int(... |
We first have to create a PhotoImage object and give
it a name. Here is an example:
cheetah_image = PhotoImage(file='cheetahs.gif')
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158 _CHAPTER 16. |
GUI PROGRAMMING II_
Here are some examples of putting the image into widgets:
label = Label(image=cheetah_image)
button = Button(image=cheetah_image, command=cheetah_callback())
You can use the configure method to set or change an image:
label.configure(image=cheetah_image)
**File types** One unfortunate limitat... |
If you would like to use other types of files, one solution is to use the Python Imaging Library,
which will be covered in Section 18.2.
###### 16.4 Canvases
A canvas is a widget on which you can draw things like lines, circles, rectangles. |
You can also draw
text, images, and other widgets on it. |
It is a very versatile widget, though we will only describe the
basics here.
**Creating canvases** The following line creates a canvas with a white background that is 200 200
_×_
pixels in size:
canvas = Canvas(width=200, height=200, bg='white')
**Rectangles** The following code draws a red rectangle to the canvas... |
The first four arguments specify the coordinates of where to place
the rectangle on the canvas. The upper left corner of the canvas is the origin, (0,0). |
The upper left
of the rectangle is at (20,100), and the lower right is at (30,150). |
If were to leave off fill='red',
the result would be a rectangle with a black outline.
**Ovals and lines** Drawing ovals and lines is similar. |
The image above on the right is created with
the following code:
-----
_16.5. |
CHECK BUTTONS AND RADIO BUTTONS_ 159
canvas.create_rectangle(20,100,70,180)
canvas.create_oval(20,100,70,180, fill='blue')
canvas.create_line(20,100,70,180, fill='green')
The rectangle is here to show that lines and ovals work similarly to rectangles. |
The first two coordinates are the upper left and the second two are the lower right.
To get a circle with radius r and center (x,y), we can create the following function:
**def create_circle(x,y,r):**
canvas.create_oval(x-r,y-r,x+r,y+r)
**Images** We can add images to a canvas. |
Here is an example:
cheetah_image = PhotoImage(file='cheetahs.gif')
canvas.create_image(50,50, image=cheetah_image)
The two coordinates are where the center of the image should be.
**Naming things, changing them, moving them, and deleting them** We can give names to the
things we put on the canvas. |
We can then use the name to refer to the object in case we want to
move it or remove it from the canvas. |
Here is an example were we create a rectangle, change its
color, move it, and then delete it:
rect = canvas.create_rectangle(0,0,20,20)
canvas.itemconfigure(rect, fill='red')
canvas.coords(rect,40,40,60,60)
canvas.delete(rect)
The coords method is used to move or resize an object and the delete method is used to dele... |
If you want to delete everything from the canvas, use the following:
canvas.delete(ALL)
###### 16.5 Check buttons and Radio buttons
In the image below, the top line shows a check button and the bottom line shows a radio button.
**Check buttons** The code for the above check button is:
show_totals = IntVar()
chec... |
GUI PROGRAMMING II_
The one thing to note here is that we have to tie the check button to a variable, and it can’t be
just any variable, it has to be a special kind of Tkinter variable, called an IntVar. |
This variable,
show_totals, will be 0 when the check button is unchecked and 1 when it is checked. |
To access
the value of the variable, you need to use its get method, like this:
show_totals.get()
You can also set the value of the variable using its set method. |
This will automatically check or
uncheck the check button on the screen. |
For instance, if you want the above check button checked
at the start of the program, do the following:
show_totals = IntVar()
show_totals.set(1)
check = Checkbutton(text='Show totals', var=show_totals)
**Radio buttons** Radio buttons work similarly. |
The code for the radio buttons shown at the start of
the section is:
color = IntVar()
redbutton = Radiobutton(text='Red', var=color, value=1)
greenbutton = Radiobutton(text='Green', var=color, value=2)
bluebutton = Radiobutton(text='Blue', var=color, value=3)
The value of the IntVar object color will be 1, 2, or 3, d... |
These values are controlled by the value option, specified when we create
the radio buttons.
**Commands** Both check buttons and radio buttons have a command option, where you can set a
callback function to run whenever the button is selected or unselected.
###### 16.6 Text widget
The Text widget is a bigger, more p... |
Here is an example of
creating one:
textbox = Text(font=('Verdana', 16), height=6, width=40)
The widget will be 40 characters wide and 6 rows tall. |
You can still type past the sixth row; the
widget will just display only six rows at a time, and you can use the arrow keys to scroll.
If you want a scrollbar associated with the text box you can use the ScrolledText widget. |
Other
than the scrollbar, ScrolledText works more or less the same as Text. An example is of what it
looks like is shown below. |
To use the ScrolledText widget, you will need the following import:
**from tkinter.scrolledtext import ScrolledText**
-----
_16.7. |
SCALE WIDGET_ 161
Here are a few common commands:
Statement Description
textbox.get(1.0,END) returns the contents of the text box
textbox.delete(1.0,END) deletes everything in the text box
textbox.insert(END,'Hello') inserts text at the end of the text box
One nice option when declaring the Text widget is undo=Tr... |
There are a ton of other things you can do with the Text widget. |
It is
almost like a miniature word processor.
###### 16.7 Scale widget
A Scale is a widget that you can slide back and forth to select different values. |
An example is
shown below, followed by the code that creates it.
scale = Scale(from_=1, to_=100, length=300, orient='horizontal')
Here are some of the useful options of the Scale widget:
Option Description
from_ minimum value possible by dragging the scale
to_ maximum value possible by dragging the scale
length... |
One way is to link it with
an IntVar just like with check buttons and radio buttons, using the variable option. Another
option is to use the scale’s get and set methods. |
A third way is to use the command option, which
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162 _CHAPTER 16. |
GUI PROGRAMMING II_
works just like with buttons.
###### 16.8 GUI Events
Often we will want our programs to do something if the user presses a certain key, drags something
on a canvas, uses the mouse wheel, etc. |
These things are called events.
**A simple example** The first GUI program we looked at back in Section 15.1 was a simple temperature converter. |
Anytime we wanted to convert a temperature we would type in the temperature
in the entry box and click the Calculate button. |
It would be nice if the user could just press the
enter key after they type the temperature instead of having to click to Calculate button. |
We can
accomplish this by adding one line to the program:
entry.bind('<Return>', lambda dummy=0:calculate())
This line should go right after you declare the entry box. |
What it does is it takes the event that the
enter (return) key is pressed and binds it to the calculate function.
Well, sort of. |
The function you bind the event to is supposed to be able to receive a copy of an Event
object, but the calculate function that we had previously written takes no arguments. |
Rather than
rewrite the function, the line above uses lambda trick to essentially throw away the Event object.
**Common events** Here is a list of some common events:
Event Description
<Button-1> The left mouse button is clicked.
<Double-Button-1> The left mouse button is double-clicked.
<Button-Release-1> The lef... |
Button 2
is the middle button and button 3 is the right button.
The most useful attributes in the Event object are:
-----
_16.8. |
GUI EVENTS_ 163
Attribute Description
keysym The name of the key that was pressed
x, y The coordinates of the mouse pointer
delta The value of the mouse wheel
**Key events** For key events, you can either have specific callbacks for different keys or catch all
keypresses and deal with them in the same callback. |
Here is an example of the latter:
**from tkinter import ***
**def callback(event):**
**print(event.keysym)**
root = Tk()
root.bind('<Key>', callback)
mainloop()
The above program prints out the names of the keys that were pressed. |
You can use those names
in if statements to handle several different keypresses in the callback function, like below:
**if event.keysym == 'percent':**
_# percent (shift+5) was pressed, do something about it..._
**elif event.keysym == 'a':**
_# lowercase a was pressed, do something about it..._
|y events For key e... |
Here is an example of the latter:|Col2|
|---|---|
|||
|from tkinter import * def callback(event): print(event.keysym) root = Tk() root.bind('<Key>', callback) mainloop()||
Use the single callback method if you are catching a lot of keypresses and are doing something
similar with all of them. |
On the other hand, if you just want to catch a couple of specific keypresses
or if certain keys have very long and specific callbacks, you can catch keypresses separately like
below:
**from tkinter import ***
**def callback1(event):**
**print('You pressed the enter key.')**
**def callback2(event):**
**print('You p... |
You can use the program
from earlier in this section to find the names of all the keys. |
Here are the names for a few common
keys:
|e the single callback method if you are catching a lot of keypresses and are doing something ilar with all of them. |
On the other hand, if you just want to catch a couple of specific keypresses f certain keys have very long and specific callbacks, you can catch keypresses separately like ow:|Col2|
|---|---|
|||
|from tkinter import * def callback1(event): print('You pressed the enter key.') def callback2(event): print('You pressed th... |
GUI PROGRAMMING II_
Tkinter name Common name
<Return> Enter key
<Tab> Tab key
<Space> Spacebar
<F1>, ..., <F12> F1, ..., F12
<Next>, <Prior> Page up, Page down
<Up>, <Down>, <Left>, <Right> Arrow keys
<Home>, <End> Home, End
<Insert>, <Delete> Insert, Delete
<Caps_Lock>, <Num_Lock> Caps lock, Number lock
<Co... |
You can also catch key
combinations, such as <Shift-F5>, <Control-Next>, <Alt-2>, or <Control-Shift-F1>.
**Note** These examples all bind keypresses to root, which is our name for the main window. |
You
can also bind keypresses to specific widgets. |
For instance, if you only want the left arrow key to
work on a Canvas called canvas, you could use the following:
canvas.bind(<Left>, callback)
One trick here, though, is that the canvas won’t recognize the keypress unless it has the GUI’s focus.
This can be done as below:
canvas.focus_set()
###### 16.9 Event e... |
EVENT EXAMPLES_ 165
move += 1
**elif event.keysym=='Left':**
move -=1
canvas.coords(rect,50+move,50,100+move,100)
root = Tk()
root.bind('<Key>', callback)
canvas = Canvas(width=200,height=200)
canvas.grid(row=0,column=0)
rect = canvas.create_rectangle(50,50,100,100,fill='blue')
move = 0
mainloop()
**Example 2** ... |
The program starts by
drawing a rectangle to the screen. |
The user can do the following:
- Drag the rectangle with the mouse (<B1_Motion>).
- Resize the rectangle with the mouse wheel (<MouseWheel>).
- Whenever the user left-clicks, the rectangle will change colors (<Button-1>).
- Anytime the mouse is moved, the current coordinates of the mouse are displayed in a ... |
GUI PROGRAMMING II_
-----
_16.9. EVENT EXAMPLES_ 167
Here are a few notes about how the program works:
1. |
First, every time the mouse is moved over the canvas, the mouse_motion_event function is
called. |
This function prints the mouse’s current coordinates which are contained in the Event
attributes x and y.
2. |
The wheel_event function is called whenever the user uses the mouse (scrolling) wheel.
The Event attribute delta contains information about how quickly and in what direction
the wheel was moved. |
We just stretch or shrink the rectangle based on whether the wheel
was moved forward or backward.
3. The b1_event function is called whenever the user presses the left mouse button. |
The function changes the color of the rectangle whenever the rectangle is clicked. There is a global
variable here called b1_drag that is important. |
It is set to True whenever the user is dragging
the rectangle. When dragging is going on, the left mouse button is down and the b1_event
function is continuously being called. |
We don’t want to keep changing the color of the rectangle in that case, hence the if statement.
4. |
The dragging is accomplished mostly in the b1_motion_event function, which is called
whenever the left mouse button is down and the mouse is being moved. |
It uses global variables that keep track of what the mouse’s position was the last time the function was called,
and then moves the rectangle according to the difference between the new and old position.
When the dragging is down, the left mouse button will be released. |
When that happens, the
b1_release_event function is called, and we set the global b1_drag variable accordingly.
5. |
The focus_set method is needed because the canvas will not recognize the mouse wheel
events unless the focus is on the canvas.
6. |
One problem with this program is that the user can modify the rectangle by clicking anywhere
on the canvas, not just on rectangle itself. |
If we only want the changes to happen when the
mouse is over the rectangle, we could specifically bind the rectangle instead of the whole
canvas, like below:
canvas.tag_bind(rect, '<B1-Motion>', b1_motion_event)
-----
168 _CHAPTER 16. |
GUI PROGRAMMING II_
7. Finally, the use of global variables here is a little messy. |
If this were part of a larger project, it
might make sense to wrap all of this up into a class.
-----
### Chapter 17
## GUI Programming III
This chapter contains a few more GUI odds and ends.
###### 17.1 Title bar
The GUI window that Tkinter creates says Tk by default. |
Here is how to change it:
root.title('Your title')
###### 17.2 Disabling things
Sometimes you want to disable a button so it can’t be clicked. |
Buttons have an attribute state that
allows you to disable the widget. Use state=DISABLED to disable the button and state=NORMAL
to enable it. |
Here is an example that creates a button that starts out disabled and then enables it:
button = Button(text='Hi', state=DISABLED, command=function)
button.configure(state=NORMAL)
You can use the state attribute to disable many other types of widgets, too.
###### 17.3 Getting the state of a widget
Sometimes, you nee... |
The cget method is used for this. For example, the following gets the text of
a label called label:
label.cget('text')
169
-----
170 _CHAPTER 17. |
GUI PROGRAMMING III_
This can be used with buttons, canvases, etc., and it can be used with any of their properties, like
bg, fg, state, etc. |
As a shortcut, Tkinter overrides the [] operators, so that label['text']
accomplishes the same thing as the example above.
###### 17.4 Message boxes
Message boxes are windows that pop up to ask you a question or say something and then go away.
To use them, we need an import statement:
**from tkinter.messagebox impor... |
For each of them you can specify the
message the user will see as well as the title of the message box. |
Here are three types of message
boxes, followed by the code that generates them:
showinfo(title='Message for you', message='Hi There!')
askquestion(title='Quit?', message='Do you really want to quit?')
showwarning(title='Warning', message='Unsupported format')
Below is a list of all the types of message boxes. |
Each displays a message in its own way.
Message Box Special properties
showinfo OK button
askokcancel OK and Cancel buttons
askquestion Yes and No buttons
askretrycancel Retry and a Cancel buttons
askyesnocancel Yes, No, and Cancel buttons
showerror An error icon and an OK button
showwarning A warning icon and ... |
See the next section for a
simple example of using the return value. Here is a table of the return values:
-----
_17.5. |
DESTROYING THINGS_ 171
Function Return value (based on what user clicks)
showinfo Always returns 'ok'
askokcancel OK—True Cancel or window closed—False
askquestion Yes—'yes' No—'no'
askretrycancel Retry—True Cancel or window closed—False
askyesnocancel Yes—True No—False anything else—None
showerror Always return... |
For instance, to get rid of a button called button,
do the following:
button.destroy()
To get rid of the entire GUI window, use the following:
root.destroy()
**Stopping a window from being closed** When your user tries to close the main window, you may
want to do something, like ask them if they really want to ... |
Here is a way to do that:
**from tkinter import ***
**from tkinter.messagebox import askquestion**
**def quitter_function():**
answer = askquestion(title='Quit?', message='Really quit?')
**if answer=='yes':**
root.destroy()
root = Tk()
root.protocol('WM_DELETE_WINDOW', quitter_function)
mainloop()
The key is the ... |
Here is a way to do that:|Col2|
|---|---|
|||
|from tkinter import * from tkinter.messagebox import askquestion def quitter_function(): answer = askquestion(title='Quit?', message='Really quit?') if answer=='yes': root.destroy() root = Tk() root.protocol('WM_DELETE_WINDOW', quitter_function) mainloop()||
root.protoco... |
For instance, in
a function triggered by a button press, Tkinter will not update the screen until the function is done.
-----
172 _CHAPTER 17. |
GUI PROGRAMMING III_
If, in that function, you want to change something on the screen, pause for a short while, and then
change something else, you will need to tell Tkinter to update the screen before the pause. |
To do
that, just use this:
root.update()
If you only want to update a certain widget, and nothing else, you can use the update method of
that widget. |
For example,
canvas.update()
A related thing that is occasionally useful is to have something happen after a scheduled time
interval. For instance, you might have a timer in your program. |
For this, you can use the after
method. Its first argument is the time in milliseconds to wait before updating and the second
argument is the function to call when the time is right. |
Here is an example that implements a timer:
**from time import time**
**from tkinter import ***
**def update_timer():**
time_left = int(90 - (time()-start))
minutes = time_left // 60
seconds = time_left % 60
time_label.configure(text='{}:{:02d}'.format(minutes, seconds))
root.after(100, update_timer)
root = Tk()
ti... |
To use
them in Tkinter, we need the following import statement:
**from tkinter.filedialog import ***
Tkinter dialogs usually look like the ones that are native to the operating system.
|Col1|Col2|
|---|---|
|from time import time from tkinter import * def update_timer(): time_left = int(90 - (time()-start)) minutes ... |
DIALOGS_ 173
Here are the most useful dialogs:
Dialog Description
askopenfilename Opens a typical file chooser dialog
askopenfilenames Like previous, but user can pick more than one file
asksaveasfilename Opens a typical file save dialog
askdirectory Opens a directory chooser dialog
The return value of askopenfi... |
The return value of askopenfilenames
is a list of files, which is empty if no files are selected. |
The askdirectory function returns the
name of the directory chosen.
There are some options you can pass to these functions. You can set initialdir to the directory
you want the dialog to start in. |
You can also specify the file types. |
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