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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.
Tcl packages, pkg_mkIndex, pkgIndex.tcl -what are they and why use them.

In the previous article [here], I wrote about namespaces and how - as our program grows - we need to keep named pieces of code and globally accessible variable in their own groups. And we do so using a structure that's very much like family names and forenames. As our program grows, we also need to separate out various sections of the code into different files, so they can be maintained by a different person, perhaps on a different maintainance cycle, and so that common code can be called into severl programs without it being duplicated.

So every language that we teach (there's a full list of our public courses here) has some sort of capability to load code from multiple places into a single program. In Tcl, separate loading can be done on an adhoc basis via source or more flexibly and formalised via package require.

The package mechanism works as follows.

1. In the script file which contains the code for the package, use a package provide - for example:
  package provide table 1.0

2. Provide an index file in the folder in which the package is stored, called pkgIndex.tcl. In this file will be a whole load of statements which define which packages are held in which file in the directory. You could write it manually, but plese don't - there's a Tcl command called pkg_mkIndex to do it for you - and you run it in a Tcl shell as follows:
  pkg_mkIndex . *.tcl

3. In your program which requires the package, add the directory in which the package may by found to the variable called auto_path ...
  lappend auto_path furniture

4. And (finally) package require the package:
  package require table

There are complete source files from yesterday's training on our site - [the package code] and [a calling program]. You'll note that the package file defines a namesapce. Although namespaces and packages are different facilities, its natural to use them together, with a package loading in a whole bundle of pieces of code neatly wrapped in a namespace.
(written 2011-09-03)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T213 - Tcl/Tk - Libraries, Packages and Namespaces
  [146] example of Tcl namespaces and packages - (2004-12-10)
  [1339] Packages and Namespaces are like Suitcases and Aircraft - (2007-09-09)
  [1529] Tcl - learning how to use namespaces, packages and libraries together - (2008-02-02)
  [2476] Tcl - uplevel to run code at calling level - (2009-10-24)
  [3066] Separating groups of variables into namespaces - (2010-11-24)
  [3417] What is a namespace and why do we need them? - (2011-09-03)
  [4522] Loading packages in your Tcl program - (2015-10-09)


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Some other Articles
Assigning values to variables within other statements - Ruby
Ruby off the Rails?
Making best use of the new enthusiasm for Melksham
Data that we use during our training courses, and other training resources
Tcl packages, pkg_mkIndex, pkgIndex.tcl -what are they and why use them.
Storing Tcl source code encoded, and running via your own C program
User defined sorting and other uses of callbacks in Tcl and Tk
Passing back multiple results in Tcl - upvar and uplevel
If its Sunday, must it be Weymouth?
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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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