Mac/Demo/example2.html

   1 <HTML><HEAD><TITLE>Using python to create Macintosh applications, part two</TITLE></HEAD>
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   3 <H1>Using python to create Macintosh applications, part two</H1>
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   5
   6 In this document we rewrite the application of the <A
   7 HREF="example1.html">previous example</A> to use modeless dialogs. We
   8 will use an application framework, and we will have a look at creating
   9 applets, standalone applications written in Python.  The <A
  10 HREF="example2/dnslookup-2.py">source code</A> and
  11 <A HREF="example2/dnslookup-2.rsrc">resource file</A> are available in the folder
  12 <A HREF="example2">example2</A>. <p>
  13
  14 Again, we start with ResEdit to create our dialogs. Not only do we
  15 want a main dialog this time but also an "About" dialog.  This example is less
  16 than complete since we do not provide a <A NAME="bundle">BNDL resource</A>
  17 and related stuff that an application cannot be without. We are able to do this
  18 when building a python applet since BuildApplet will substitute default resources
  19 for BNDL, etc. when none are supplied (<A HREF="#no-bundle">See below</A>.)
  20 "Inside Mac" or various
  21 books on Macintosh programming will help here. Also, you can refer to
  22 the resource files provided in the Python source distribution for some
  23 of the python-specific points of BNDL programming: the
  24 "appletbundle.rsrc" file is what is used for creating applets if you
  25 don't provide your own resource file. <p>
  26
  27 When creating your own BNDL resouorces, keep in mind that the Finder gets
  28 confused if you have more than one application with the same signature. This may be due
  29 to some incorrectness on the side of "BuildApplet", I am not sure.  There is one
  30 case when you definitely need a unique signature: when you create an applet that
  31 has its own data files and you want the user to be able to start your
  32 applet by double-clicking one of the datafiles. <p>
  33
  34 Let's have a look at dnslookup-2.rsrc, our resource file. Dialog 512 is the
  35 main window which has one button (Lookup), two labels and
  36 two text entry areas, one of which is used for output only. The "Quit"
  37 button has disappeared, because its function is handled by a menu choice.  Here's
  38 what it will look like at run time:<p>
  39 <div align=center>
  40 <img width=324 height=205 src="example2/dnslookup-2.gif" alt="dialog image">
  41 </div>
  42 <p>
  43
  44 <H2>A modeless dialog application using FrameWork</H2>
  45
  46 On to the source code in <A
  47 HREF="example2/dnslookup-2.py">dnslookup-2.py</A>.  The
  48 start is similar to our previous example program <A
  49 HREF="example1/dnslookup-1.py">dnslookup-1.py</A>, with
  50 one extra module being imported. To make life more simple we will use
  51 the <CODE>FrameWork</CODE> module, a nifty piece of code that handles
  52 all the gory Mac details of event loop programming, menubar
  53 installation and all the other code that is the same for every Mac
  54 program in the world.  Like most standard modules, FrameWork will run
  55 some sample test code when you invoke it as a main program, so try it
  56 now. It will create a menu bar with an Apple menu with the about box
  57 and a "File" menu with some pythonesque choices (which do nothing
  58 interesting, by the way) and a "Quit" command that works. <p>
  59
  60 <BLOCKQUOTE>
  61 If you have not used <code>FrameWork</code> before you may want to
  62 first take a look at the <A HREF="textedit.html">Pathetic EDitor</A>
  63 example, which builds a minimal text editor using FrameWork and TextEdit.
  64 On the other hand: we don't use many features of FrameWork, so you could
  65 also continue with this document.
  66 </BLOCKQUOTE>
  67
  68 After the imports we get the definitions of resource-IDs in our
  69 resource file, slightly changed from the previous version of our
  70 program. The main program is also
  71 similar to our previous version, with one important exception: we
  72 first check to see whether our resource is available before opening
  73 the resource file. Why is this? Because later, when we will have
  74 converted the script to an applet, our resources will be available in
  75 the applet file and we don't need the separate resource file
  76 anymore. <p>
  77
  78 Next comes the definition of our main class,
  79 <CODE>DNSLookup</CODE>, which inherits
  80 <CODE>FrameWork.Application</CODE>. The Application class handles the
  81 menu bar and the main event loop and event dispatching. In the
  82 <CODE>__init__</CODE> routine we first let the base class initialize
  83 itself, then we create our modeless dialog and finally we jump into
  84 the main loop. The main loop continues until we call <CODE>self._quit</CODE>,
  85 which we will do when the user selects "Quit". When we create
  86 the instance of <CODE>MyDialog</CODE> (which inherits
  87 <CODE>DialogWindow</CODE>, which inherits <CODE>Window</CODE>) we pass
  88 a reference to the application object, this reference is used to tell
  89 Application about our new window.  This enables the event loop to keep
  90 track of all windows and dispatch things like update events and mouse
  91 clicks. <p>
  92
  93 The <CODE>makeusermenus()</CODE> method (which is called sometime
  94 during the Application <CODE>__init__</CODE> routine) creates a File
  95 menu with a Quit command (shortcut command-Q), which will callback to
  96 our quit() method. <CODE>Quit()</CODE>, in turn, calls <CODE>_quit</CODE> which
  97 causes the mainloop to terminate at a convenient time. <p>
  98
  99 Application provides a standard about box, but we override this by
 100 providing our own <CODE>do_about()</CODE> method which shows an about
 101 box from a resource as a modal dialog. This piece of code should look
 102 familiar to you from the previous example program. That do_about is
 103 called when the user selects About from the Apple menu is, again,
 104 taken care of by the __init__ routine of Application. <p>
 105
 106 The <CODE>MyDialog</CODE> class is the container for our main
 107 window. Initialization is again done by first calling the base class
 108 <CODE>__init__</CODE> function and finally setting the local variable
 109 "parent." <p>
 110
 111 <CODE>Do_itemhit()</CODE> is called when an item is selected in this
 112 dialog by the user. We are passed the item number (and the original
 113 event structure, which we normally ignore). The code is similar to the
 114 main loop of our previous example program: a switch depending on the
 115 item selected.  <CODE>Dnslookup()</CODE> is quite similar to our previous
 116 example. <p>
 117
 118 <H2><IMG SRC="html.icons/mkapplet.gif"><A NAME="applets">Creating applets</A></H2>
 119
 120 Now let us try to turn the python script into an applet, a standalone
 121 application. This will <em>not</em> work if you have the "classic 68k"
 122 Python distribution, only if you have the cfm68k or PPC distribution.
 123
 124 <blockquote>
 125 Actually, "standalone" is probably not the correct term here, since an
 126 applet does still depend on a lot of the python environment: the
 127 PythonCore shared library, the Python Preferences file, the python Lib
 128 folder and any other modules that the main module depends on. It is
 129 possible to get rid of all these dependencies and create true standalone
 130 applications in Python, but this is a bit difficult. See <a href="freezing.html">
 131 Standalone Applications in Python</a> for details. For this
 132 document, by standalone we mean here that
 133 the script has the look-and-feel of an application, including the
 134 ability to have its own document types, be droppable, etc.
 135 </blockquote>
 136
 137 The easiest way to create an applet is to take your source file and
 138 drop it onto "BuildApplet", located in the Python home
 139 folder. This will create an applet with the same name as your python
 140 source with the ".py" stripped. Also, if a resource file with the same
 141 name as your source but with ".rsrc" extension is available the
 142 resources from that file will be copied to your applet too. If there
 143 is no resource file for your script a set of default resources will be
 144 used, and the applet will have the default creator 'Pyt0'. The latter
 145 also happens if you do have a resource file but without the BNDL
 146 combo. <A NAME="no-bundle">Actually</A>, as in the present example.
 147 <p>
 148
 149 If you need slightly more control over the BuildApplet process you can
 150 double-click it, and you will get dialogs for source and
 151 destination of the applet. The rest of the process, including locating
 152 the resource file, remains the same. <p>
 153
 154 Note that though our example application completely bypasses the
 155 normal python user interface this is by no means necessary. Any python
 156 script can be turned into an applet, and all the usual features of the
 157 interpreter still work. <p>
 158
 159 That's all for this example, you may now return to the <A HREF="index.html">
 160 table of contents</A> to pick another topic. <p>
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