A Comprehensive Introduction to Python Programming and ... - MSDL

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5.3 Tkinter Variables 47 / 75 It simply stores it, even if it is not of the proper type (Python is untyped, so this is possible). Therefore, it cannot be used as is inside a try..execute block to validate data. The get( ) method, however, will fail if the value associated with the variable is erroneous. However, at this point, the previous value is lost.
6 Event Handling: bringing applications to life Every GUI does not do much without a way to handle events that are generated by the user. In fact, most of the execution time of graphical applications is spent in the event loop. Tkinter provides a very simple mechanism for event handling, but a nonetheless very precise and powerful one. 6.1 The Idea Tkinter provides an easy and convenient way to handle events by allowing callback functions to be associated with any event and any widget. In addition, very precise events can be directly described and associated with actions. For example, one could decide to only respond two two specific key press events, pressing the tabulation key or the carriage return key. While in most other languages / GUI toolkits this would require responding to the “Key Press” event and checking if the event that occured matches one of the keys we are interested in, and then executing some code depending on the result we obtained, Tkinter does it differently. It allows to bind distinct callbacks to distinct key press events, in our case one event (and one callback) for the tabulation key and one event for the carriage return key. Thus, Tkinter events do not necessarily correspond to the common event types, but they can be much more specific. Needless to say, this is a great advantage, and allows for a much cleaner implementation.
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Page 21 and 22: 2.5 Show me what you can do! 20 / 7
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Page 39 and 40: 4 Geometry Managers and Widget Plac
Page 41 and 42: 4.3 The “Grid” Geometry Manager
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