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4 | <meta name="description" content="Pmw - a toolkit for building high-level compound widgets in Python"> | |
5 | <meta name="content" content="python, megawidget, mega widget, compound widget, gui, tkinter"> | |
6 | <title>Dynamic loader</title> | |
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9 | <body bgcolor="#ffffff" text="#000000" link="#0000ee" | |
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11 | ||
12 | <h1 ALIGN="CENTER">Dynamic loader</h1> | |
13 | ||
14 | <p> | |
15 | There are two aspects of Pmw, unrelated to megawidgets, that | |
16 | require special attention. Firstly, Pmw is made up of many | |
17 | sub-modules, potentially making access to its various classes and | |
18 | functions cumbersome for the user. Secondly, Pmw is regularly | |
19 | being modified and added to, thus requiring the release of new | |
20 | versions. Therefore, techniques for making access to the | |
21 | sub-modules easy and efficient and for dealing with the different | |
22 | versions have been developed. These techniques are incorporated | |
23 | into the dynamic loader which Pmw creates when it is first | |
24 | imported.</p> | |
25 | ||
26 | <p> The first purpose of the loader is to give access to all Pmw classes | |
27 | and functions through a single entry point, the <strong>Pmw.</strong> prefix. For | |
28 | example, to access the ComboBox class (which resides in one of the | |
29 | sub-modules of Pmw), you just have to use <code>Pmw.ComboBox</code>. Without | |
30 | the loader, this would be a more complicated reference, such as, | |
31 | hypothetically, <code>Pmw.PmwComboBox.ComboBox</code>.</p> | |
32 | ||
33 | <p> The second purpose of the loader is to delay the importing of the | |
34 | sub-modules until they are needed. This improves the startup time | |
35 | of applications which only use a few Pmw megawidgets. It also | |
36 | allows more megawidgets to be added to the library without slowing | |
37 | down applications which do not use them.</p> | |
38 | ||
39 | <p> The third purpose of the loader is to allow a script using Pmw to | |
40 | specify which version of Pmw it requires. This allows an | |
41 | application to continue working correctly even after newer releases | |
42 | of Pmw have been made which are not compatible with the version | |
43 | expected by the application. Several versions of Pmw can be | |
44 | installed at once, with the actual version used being specified by | |
45 | each application. In addition, the loader can be configured to | |
46 | search in one or more alpha versions of Pmw. These versions may | |
47 | contain new megawidgets, or new versions of existing megawidgets, | |
48 | that are currently not in the base releases.</p> | |
49 | ||
50 | <p> Several functions are available to set and query the version of | |
51 | Pmw being used. These are <code>Pmw.setversion()</code> and | |
52 | <code>Pmw.setalphaversions()</code> which specify the version and alpha | |
53 | versions (if any) to use for this session; <code>Pmw.version()</code> which | |
54 | returns the version(s) being used by this session; and | |
55 | <code>Pmw.installedversions()</code> which returns the version(s) of Pmw | |
56 | currently installed. These are described in the | |
57 | <a href="PmwFunctions.html">Pmw functions reference manual</a>.</p> | |
58 | ||
59 | <p> When Pmw is first imported, an instance of PmwLoader is created | |
60 | and placed into <code>sys.modules['Pmw']</code>. From that point on, any | |
61 | reference to attributes of the Pmw 'module' is handled by the | |
62 | loader. The real Pmw package is stored in <code>sys.modules['_Pmw']</code>.</p> | |
63 | ||
64 | <p> The loader searches the Pmw package base directory for | |
65 | sub-directories with the prefixes <code>Pmw_</code> and <code>Alpha_</code>, which | |
66 | contain Pmw base releases and alpha releases. The version numbers | |
67 | are given by the part of the directory name following the prefix. | |
68 | These versions are available for use and are those returned by the | |
69 | <code>Pmw.installedversions</code> function. The initial version is set to | |
70 | the base release with the greatest version number. When the first | |
71 | reference to a Pmw class or function is made, the loader reads the | |
72 | files named <strong>Pmw.def</strong> in the current base version directory and | |
73 | also in the alpha directories (if any). These files list all the | |
74 | classes and functions supported by the version. Pmw attributes | |
75 | are first searched for in the alpha directories and then in the | |
76 | base version directory. The first directory which supports the | |
77 | reference is used. In this way, alpha versions override base | |
78 | versions.</p> | |
79 | ||
80 | <p> The directory <code>Alpha_99_9_example</code> contains a simple example of | |
81 | how to structure an alpha version. The following code can be used | |
82 | to request that the alpha version be used and then creates an | |
83 | instance of a new megawidget defined in the alpha version.</p> | |
84 | ||
85 | <dl><dd><pre> import Pmw | |
86 | Pmw.setalphaversions('99.9.example') | |
87 | ||
88 | # Create a standard message dialog using the base Pmw version. | |
89 | ordinary = Pmw.MessageDialog( | |
90 | message_text = 'Ordinary\nPmw Dialog') | |
91 | ||
92 | # Create an example dialog using the alpha Pmw version. | |
93 | alpha = Pmw.AlphaExample()</pre></dd></dl> | |
94 | ||
95 | <p> <strong>Freezing Pmw</strong></p> | |
96 | ||
97 | <p> Since the dynamic loader requires that Pmw be installed at run | |
98 | time, it can not be used when <em>freezing</em> Pmw. In this case, a | |
99 | single module containing all Pmw code is required, which can then | |
100 | be frozen with the rest of the application's modules. The | |
101 | <code>bundlepmw.py</code> script in the Pmw <code>bin</code> directory can be used to | |
102 | create such a file. This script concatenates (almost) all Pmw | |
103 | megawidget files into a single file, <code>Pmw.py</code>, which it writes to | |
104 | the current directory. The script is called like this:</p> | |
105 | ||
106 | <dl><dd><pre> bundlepmw.py [-noblt] [-nocolor] /path/to/Pmw/Pmw_X_X_X/lib</pre></dd></dl> | |
107 | ||
108 | <p> The last argument should be the path to the <code>lib</code> directory of the | |
109 | required version of Pmw. By default, the <code>Pmw.py</code> file imports | |
110 | the <code>PmwBlt</code> and <code>PmwColor</code> modules and so, to freeze an | |
111 | application using Pmw, you will need to copy the files <code>PmwBlt.py</code> | |
112 | and <code>PmwColor.py</code> to the application directory before freezing.</p> | |
113 | ||
114 | <p> If you are sure that your application does not use any of the | |
115 | <code>Pmw.Blt</code> or <code>Pmw.Color</code> functions, you can use the <code>-noblt</code> or | |
116 | <code>-nocolor</code> options. In this case <code>Pmw.py</code> will be modified so | |
117 | that it does not import these module(s) and so will not need to be | |
118 | included when freezing the application.</p> | |
119 | ||
120 | <p> If your application only uses a few Pmw megawidgets, you can | |
121 | remove the references to the usused ones in the <code>files</code> list in | |
122 | the <code>bundlepmw.py</code> code. To make the change, take a copy of the | |
123 | script and modify it. This will make the <code>Pmw.py</code> file smaller. | |
124 | However, be sure that you do not delete megawidgets that are | |
125 | components or base classes of megawidgets that you use.</p> | |
126 | ||
127 | <p></p> | |
128 | ||
129 | ||
130 | ||
131 | <center><P ALIGN="CENTER"> | |
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133 | </p></center> | |
134 | ||
135 | ||
136 | <font size=-1> | |
137 | <center><P ALIGN="CENTER"> | |
138 | Pmw 1.2 - | |
139 | 5 Aug 2003 | |
140 | - <a href="index.html">Home</a> | |
141 | ||
142 | </p></center> | |
143 | </font> | |
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