projects / OpenSPARC-T2-SAM / blame
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| 54 | <H3><A NAME="SECTION0082153000000000000000"></A><A NAME="optparse-other-reasons-to-extend-optparse"></A> | |
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| 56 | 6.21.5.3 Other reasons to extend <tt class="module">optparse</tt> | |
| 57 | </H3> | |
| 58 | ||
| 59 | <P> | |
| 60 | Adding new types and new actions are the big, obvious reasons why you | |
| 61 | might want to extend <tt class="module">optparse</tt>. I can think of at least two other areas to | |
| 62 | play with. | |
| 63 | ||
| 64 | <P> | |
| 65 | First, the simple one: OptionParser tries to be helpful by calling | |
| 66 | <tt class="function">sys.exit()</tt> when appropriate, i.e. when there's an error on the | |
| 67 | command line or when the user requests help. In the former case, the | |
| 68 | traditional course of letting the script crash with a traceback is | |
| 69 | unacceptable; it will make users think there's a bug in your script when | |
| 70 | they make a command-line error. In the latter case, there's generally | |
| 71 | not much point in carrying on after printing a help message. | |
| 72 | ||
| 73 | <P> | |
| 74 | If this behaviour bothers you, it shouldn't be too hard to ``fix'' it. | |
| 75 | You'll have to | |
| 76 | ||
| 77 | <DL COMPACT> | |
| 78 | <DT> | |
| 79 | ||
| 80 | 1) | |
| 81 | <DD> | |
| 82 | subclass OptionParser and override <tt class="method">error()</tt> | |
| 83 | ||
| 84 | <P> | |
| 85 | <DT> | |
| 86 | ||
| 87 | 2) | |
| 88 | <DD> | |
| 89 | subclass Option and override <tt class="method">take_action()</tt>--you'll | |
| 90 | need to provide your own handling of the <tt class="member">help</tt> action that | |
| 91 | doesn't call <tt class="function">sys.exit()</tt> | |
| 92 | ||
| 93 | <P> | |
| 94 | </DD> | |
| 95 | </DL> | |
| 96 | ||
| 97 | <P> | |
| 98 | The second, much more complex, possibility is to override the | |
| 99 | command-line syntax implemented by <tt class="module">optparse</tt>. In this case, you'd leave the | |
| 100 | whole machinery of option actions and types alone, but rewrite the code | |
| 101 | that processes <var>sys.argv</var>. You'll need to subclass OptionParser in any | |
| 102 | case; depending on how radical a rewrite you want, you'll probably need | |
| 103 | to override one or all of <tt class="method">parse_args()</tt>, <tt class="method">_process_long_opt()</tt>, and | |
| 104 | <tt class="method">_process_short_opts()</tt>. | |
| 105 | ||
| 106 | <P> | |
| 107 | Both of these are left as an exercise for the reader. I have not tried | |
| 108 | to implement either myself, since I'm quite happy with <tt class="module">optparse</tt>'s default | |
| 109 | behaviour (naturally). | |
| 110 | ||
| 111 | <P> | |
| 112 | Happy hacking, and don't forget: Use the Source, Luke. | |
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