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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
The magic of -textvariable

If you're writing a GUI based application, you'll need to hold pertinent information in variables in your program, AND display that pertinent information to the user.

The obvious way of doing this is to provide code that updates the display as required - in the case of Tcl/Tk you might write
   .wname configure -text "Melksham"
to change the text on the button called "wname" to Melksham, and
   set usersays [.wenter cget -text]
to read the text that the user's put into an entry box.

But there's a better alternative. Many widgets support the -textvariable option which allows the widget to be a reflection of the variable in your program all the time - in other words, if your program changes a variable then it will be automatically updated within the widget display, and if the user changes text within an entry box that's set up with this feature, then the variable within your program is automatically updated. Examples:
   entry .username -textvariable uname
   label .host -textvariable hostsystemname

Complete source code examples -
A Tcl/Tk form
In a Tcl/Tk popup message box
A Perl/Tk example
(written 2006-02-08, updated 2006-06-05)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T223 - Tcl/Tk - Textish Widgets
  [1475] Tcl/Tk - updating your display while tasks are running - (2007-12-16)

P307 - Perl/Tk
  [595] Add a friendly front end with Tk - (2006-02-08)
  [599] Perl/Tk real time display - (2006-02-10)
  [738] (Perl) Callbacks - what are they? - (2006-05-30)
  [1310] Callbacks - a more complex code sandwich - (2007-08-19)
  [1340] Tk locks up - 100% c.p.u. on a simple program (Tcl, Perl, Python) - (2007-09-09)
  [3009] Expect in Perl - a short explanation and a practical example - (2010-10-22)


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The magic of -textvariable
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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