mirror of https://github.com/python/cpython
- Added a file dialog example
- Added pointers to library documentation
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Jack Jansen
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<HTML><HEAD><TITLE>Using python to create Macintosh applications, part zero</TITLE></HEAD>
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<BODY>
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<H1>Using python to create Macintosh applications, part zero</H1>
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<HR>
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This document will show you how to create a simple mac-style
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application using Python. We will glance at how to use file dialogs and
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messages. <p>
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Our example program <a href="example0/checktext.py">checktext.py</a> asks
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the user for a text file and checks what style end-of-lines the file has.
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This may need a little explanation: ASCII text files are almost identical
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on different machines, with one exception:
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<ul>
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<li> Unix systems terminate lines with the "linefeed" character, <code>0x0a</code>,
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<li> Macintoshes terminate lines with the "carriage return" character,
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<code>0x0d</code> and
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<li> MSDOS systems terminate lines with first a carriage return and then a linefeed.
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</ul>
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Let us have a look at the program. The first interesting statement in the main
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program is the call to <code>macfs.PromptGetFile</code>. This is one of the routines
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that allow you to ask the user to specify a file. You pass it one required
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argument, the prompt string. There are up to four optional MacOS <em>file type</em> arguments
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you can pass, as 4-byte strings. Specifying no file
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type will allow the user to select any file, specifying one or more types restricts
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the user to files of this type. File types are explained in most books on the Mac. <p>
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<code>PromptGetFile</code> returns two values: an <em>FSSpec</em> object and a
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success indicator. The FSSpec object is the "official" MacOS way of specifying a
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file, more on it later. The success indicator tells you whether the user clicked OK
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or Cancel. In the event of Cancel we simply exit back to the finder. <p>
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<code>PromptGetFile</code> has a number of friends that do similar things:
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<ul>
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<li> <code>StandardGetFile</code> is identical to <code>PromptGetFile</code> but
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without the prompt. It has up to four optional filetype arguments.
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<li> <code>StandardPutFile</code> asks the user for an output file. It will
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warn the user when she tries to overwrite an existing file. The routine has one
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mandatory argument: a prompt string. Pass the empty string if you do not want a prompt.
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<li> <code>GetDirectory</code> asks the user for a folder (or directory, in unix terms).
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It has one optional argument: a prompt string.
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</ul>
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All routines return an FSSpec and a success indicator. <p>
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There are many things you can do with FSSpec objects (see the
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<a href="http://www.python.org/doc/lib/macfs.html">macfs</a> section in the
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<a href="http://www.python.org/doc/lib/Top.html">Python Library Reference</a>
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for details), but passing them to <code>open</code> is not
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one of them. For this, we first have to convert the FSSpec object to a pathname, with
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the <code>as_pathname</code> method. This returns a standard MacOS-style pathname with
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colon-separated components. This can then be passed to <code>open</code>. Note that
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we call open with mode parameter <code>'rb'</code>: we want to read the file in binary
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mode. Python, like C and C++, uses unix-style line endings internally and opening a
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file in text mode (<code>'r'</code>) would result in conversion of carriage-returns to
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linefeeds upon reading. This is something that Mac and DOS programmers are usually aware
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of but that never ceases to amaze unix buffs. <p>
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After we open the file we attempt to read all data into memory. If this fails we use
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<code>EasyDialogs.Message</code> to display a message in a standard dialog box and exit.
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The EasyDialogs module has a few more useful simple dialog routines, more on that in
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<a href="example1.html">example 1</a>. <p>
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The rest of the code is pretty straightforward: we check that the file actually contains
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data, count the number of linefeeds and returns and display a message with our guess of the
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end-of-line convention used in the file. <p>
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The <a href="example0">example0</a> folder has three text files in Mac, Unix and DOS style
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for you to try the program on. After that, you can continue with <a href="example1.html">example 1</a>
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or go back to the <a href="index.html">index</a> to find another interesting topic. <p>
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<HR>
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<A HREF="http://www.cwi.nl/~jack">Jack Jansen</A>,
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<A HREF="mailto:jack@cwi.nl">jack@cwi.nl</A>, 18-July-1996.
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</BODY></HTML>
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"""checktext - Check that a text file has macintosh-style newlines"""
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import macfs
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import sys
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import EasyDialogs
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import string
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def main():
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fsspec, ok = macfs.PromptGetFile('File to check end-of-lines in:', 'TEXT')
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if not ok:
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sys.exit(0)
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pathname = fsspec.as_pathname()
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fp = open(pathname, 'rb')
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try:
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data = fp.read()
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except MemoryError:
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EasyDialogs.Message('Sorry, file is too big.')
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sys.exit(0)
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if len(data) == 0:
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EasyDialogs.Message('File is empty.')
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sys.exit(0)
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number_cr = string.count(data, '\r')
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number_lf = string.count(data, '\n')
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if number_cr == number_lf == 0:
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EasyDialogs.Message('File contains no lines.')
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if number_cr == 0:
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EasyDialogs.Message('File has unix-style line endings')
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elif number_lf == 0:
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EasyDialogs.Message('File has mac-style line endings')
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elif number_cr == number_lf:
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EasyDialogs.Message('File probably has MSDOS-style line endings')
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else:
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EasyDialogs.Message('File has no recognizable line endings (binary file?)')
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sys.exit(0)
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if __name__ == '__main__':
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main()
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@ -19,6 +19,12 @@ HREF="http://www-acs.ucsd.edu/~jstrout/python/">
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http://www-acs.ucsd.edu/~jstrout/python/</A>.
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<P>
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The <a href="http://www.python.org/doc/lib/Top.html">Python Library Reference</a> contains a section on
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<a href="http://www.python.org/doc/lib/Macintosh-Specific-Services.html">Macintosh-specific modules</a>
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that you should also read. Documentation is also available in PostScript and other
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forms, see the <a href="http://www.python.org/doc/">documentation</a> section
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on the webserver. <p>
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Some of these documents were actually written while I was working on a "real"
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project: creating a single-button application that will allow my
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girlfriend to read her mail (which actually pass thry <EM>my</EM>
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@ -36,6 +42,12 @@ with earlier versions of Python, some will definitely not.
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<H2>Table of contents</H2>
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<UL>
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<LI>
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<A HREF="example0.html">Using python to create Macintosh applications,
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part zero</A> whets your appetite by showing you how to ask the user
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for a filename, and how to display a message. It explains about end-of-line
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confusion while doing so.
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<LI>
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<A HREF="example1.html">Using python to create Macintosh applications,
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part one</A> explains how to create a simple modal-dialog application
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@ -111,4 +123,5 @@ documentation. <p>
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<HR>
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<A HREF="http://www.cwi.nl/~jack">Jack Jansen</A>,
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<A HREF="mailto:jack@cwi.nl">jack@cwi.nl</A>, 18-May-1996.
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<A HREF="mailto:jack@cwi.nl">jack@cwi.nl</A>, 18-July-1996.
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</BODY></HTML>
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@ -4,7 +4,6 @@
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</HEAD>
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<BODY>
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<H1>Using Python on the Macintosh</H1>
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<EM>(preliminary)</EM>
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<HR>
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This document is an introduction to using Python on the Apple
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@ -369,6 +368,10 @@ will appear to be correct in the editor but cause strange errors when
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imported. BBEdit has a popup menu which allows you to inspect (and
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set) the end-of-line convention used in a file. <p>
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<h2>Where to go from here</h2>
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The next section to check out is the <a href="index.html">annotated sample programs</a>.<p>
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<HR>
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<A HREF="http://www.cwi.nl/~jack">Jack Jansen</A>,
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<A HREF="mailto:jack@cwi.nl">jack@cwi.nl</A>, 19-Apr-1996.
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