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# Python - Tkinter Button

The Button widget is used to add buttons in a Python application. These buttons can display text or images that convey the purpose of the buttons. You can attach a function or a method to a button, which is called automatically when you click the button.

## Syntax:

Here is the simple syntax to create this widget:

    w = Button ( master, option=value, ... )

## Parameters:

- master: This represents the parent window.

- options: Here is the list of most commonly used options for this widget. These options can be used as key-value pairs separated by commas.

Option | Description
--- | ---
activebackground | Background color when the button is under the cursor.
activeforeground | Foreground color when the button is under the cursor.
bd | Border width in pixels. Default is 2.
bg | Normal background color.
command | Function or method to be called when the button is clicked.
fg | Normal foreground (text) color.
font | Text font to be used for the button's label.
height | Height of the button in text lines (for textual buttons) or pixels (for images).
highlightcolor | The color of the focus highlight when the widget has focus.
image | Image to be displayed on the button (instead of text).
justify | How to show multiple text lines: LEFT to left-justify each line; CENTER to center them; or RIGHT to right-justify.
padx | Additional padding left and right of the text.
pady | Additional padding above and below the text.
relief | Relief specifies the type of the border. Some of the values are SUNKEN, RAISED, GROOVE, and RIDGE.
state | Set this option to DISABLED to gray out the button and make it unresponsive. Has the value ACTIVE when the mouse is over it. Default is NORMAL.
underline | Default is -1, meaning that no character of the text on the button will be underlined. If nonnegative, the corresponding text character will be underlined.
width | Width of the button in letters (if displaying text) or pixels (if displaying an image).
wraplength | If this value is set to a positive number, the text lines will be wrapped to fit within this length.

## Methods:

Following are commonly used methods for this widget:

Medthod | Description
--- | ---
flash() | Causes the button to flash several times between active and normal colors. Leaves the button in the state it was in originally. Ignored if the button is disabled.
invoke() | Calls the button's callback, and returns what that function returns. Has no effect if the button is disabled or there is no callback.

## Example:

Try following example yourself:

    import Tkinter
    import tkMessageBox

    top = Tkinter.Tk()

    def helloCallBack():
       tkMessageBox.showinfo( "Hello Python", "Hello World")

    B = Tkinter.Button(top, text ="Hello", command = helloCallBack)

    B.pack()
    top.mainloop()

This would produce following result:

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