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| 54 | <H3><A NAME="SECTION0082149000000000000000"></A><A NAME="optparse-callback-example-6"></A> | |
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| 56 | 6.21.4.9 Callback example 6: variable arguments | |
| 57 | </H3> | |
| 58 | ||
| 59 | <P> | |
| 60 | Things get hairy when you want an option to take a variable number of | |
| 61 | arguments. For this case, you must write a callback, as <tt class="module">optparse</tt> doesn't | |
| 62 | provide any built-in capabilities for it. And you have to deal with | |
| 63 | certain intricacies of conventional <span class="Unix">Unix</span> command-line parsing that <tt class="module">optparse</tt> | |
| 64 | normally handles for you. In particular, callbacks should implement | |
| 65 | the conventional rules for bare <code>"-"</code> and <code>"-"</code> arguments: | |
| 66 | ||
| 67 | <UL> | |
| 68 | <LI> | |
| 69 | either <code>"-"</code> or <code>"-"</code> can be option arguments | |
| 70 | ||
| 71 | <P> | |
| 72 | </LI> | |
| 73 | <LI> | |
| 74 | bare <code>"-"</code> (if not the argument to some option): halt command-line | |
| 75 | processing and discard the <code>"-"</code> | |
| 76 | ||
| 77 | <P> | |
| 78 | </LI> | |
| 79 | <LI> | |
| 80 | bare <code>"-"</code> (if not the argument to some option): halt command-line | |
| 81 | processing but keep the <code>"-"</code> (append it to <code>parser.largs</code>) | |
| 82 | ||
| 83 | <P> | |
| 84 | </LI> | |
| 85 | </UL> | |
| 86 | ||
| 87 | <P> | |
| 88 | If you want an option that takes a variable number of arguments, there | |
| 89 | are several subtle, tricky issues to worry about. The exact | |
| 90 | implementation you choose will be based on which trade-offs you're | |
| 91 | willing to make for your application (which is why <tt class="module">optparse</tt> doesn't support | |
| 92 | this sort of thing directly). | |
| 93 | ||
| 94 | <P> | |
| 95 | Nevertheless, here's a stab at a callback for an option with variable | |
| 96 | arguments: | |
| 97 | <div class="verbatim"><pre> | |
| 98 | def vararg_callback(option, opt_str, value, parser): | |
| 99 | assert value is None | |
| 100 | done = 0 | |
| 101 | value = [] | |
| 102 | rargs = parser.rargs | |
| 103 | while rargs: | |
| 104 | arg = rargs[0] | |
| 105 | ||
| 106 | # Stop if we hit an arg like "--foo", "-a", "-fx", "--file=f", | |
| 107 | # etc. Note that this also stops on "-3" or "-3.0", so if | |
| 108 | # your option takes numeric values, you will need to handle | |
| 109 | # this. | |
| 110 | if ((arg[:2] == "--" and len(arg) > 2) or | |
| 111 | (arg[:1] == "-" and len(arg) > 1 and arg[1] != "-")): | |
| 112 | break | |
| 113 | else: | |
| 114 | value.append(arg) | |
| 115 | del rargs[0] | |
| 116 | ||
| 117 | setattr(parser.values, option.dest, value) | |
| 118 | ||
| 119 | [...] | |
| 120 | parser.add_option("-c", "--callback", | |
| 121 | action="callback", callback=varargs) | |
| 122 | </pre></div> | |
| 123 | ||
| 124 | <P> | |
| 125 | The main weakness with this particular implementation is that negative | |
| 126 | numbers in the arguments following <code>"-c"</code> will be interpreted as | |
| 127 | further options (probably causing an error), rather than as arguments to | |
| 128 | <code>"-c"</code>. Fixing this is left as an exercise for the reader. | |
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