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| 55 | <H3><A NAME="SECTION0082139000000000000000"></A><A NAME="optparse-conflicts-between-options"></A> | |
| 56 | <BR> | |
| 57 | 6.21.3.9 Conflicts between options | |
| 58 | </H3> | |
| 59 | ||
| 60 | <P> | |
| 61 | If you're not careful, it's easy to define options with conflicting | |
| 62 | option strings: | |
| 63 | <div class="verbatim"><pre> | |
| 64 | parser.add_option("-n", "--dry-run", ...) | |
| 65 | [...] | |
| 66 | parser.add_option("-n", "--noisy", ...) | |
| 67 | </pre></div> | |
| 68 | ||
| 69 | <P> | |
| 70 | (This is particularly true if you've defined your own OptionParser | |
| 71 | subclass with some standard options.) | |
| 72 | ||
| 73 | <P> | |
| 74 | Every time you add an option, <tt class="module">optparse</tt> checks for conflicts with existing | |
| 75 | options. If it finds any, it invokes the current conflict-handling | |
| 76 | mechanism. You can set the conflict-handling mechanism either in the | |
| 77 | constructor: | |
| 78 | <div class="verbatim"><pre> | |
| 79 | parser = OptionParser(..., conflict_handler=handler) | |
| 80 | </pre></div> | |
| 81 | ||
| 82 | <P> | |
| 83 | or with a separate call: | |
| 84 | <div class="verbatim"><pre> | |
| 85 | parser.set_conflict_handler(handler) | |
| 86 | </pre></div> | |
| 87 | ||
| 88 | <P> | |
| 89 | The available conflict handlers are: | |
| 90 | <BLOCKQUOTE> | |
| 91 | </BLOCKQUOTE><DL> | |
| 92 | <DT><STRONG><code>error</code> (default)</STRONG></DT> | |
| 93 | <DD>assume option conflicts are a programming error and raise | |
| 94 | OptionConflictError | |
| 95 | </DD> | |
| 96 | <DT><STRONG><code>resolve</code></STRONG></DT> | |
| 97 | <DD>resolve option conflicts intelligently (see below) | |
| 98 | </DD> | |
| 99 | </DL><BLOCKQUOTE> | |
| 100 | </BLOCKQUOTE> | |
| 101 | ||
| 102 | <P> | |
| 103 | As an example, let's define an OptionParser that resolves conflicts | |
| 104 | intelligently and add conflicting options to it: | |
| 105 | <div class="verbatim"><pre> | |
| 106 | parser = OptionParser(conflict_handler="resolve") | |
| 107 | parser.add_option("-n", "--dry-run", ..., help="do no harm") | |
| 108 | parser.add_option("-n", "--noisy", ..., help="be noisy") | |
| 109 | </pre></div> | |
| 110 | ||
| 111 | <P> | |
| 112 | At this point, <tt class="module">optparse</tt> detects that a previously-added option is already | |
| 113 | using the <code>"-n"</code> option string. Since <code>conflict_handler</code> is | |
| 114 | <code>"resolve"</code>, it resolves the situation by removing <code>"-n"</code> from the | |
| 115 | earlier option's list of option strings. Now <code>"-dry-run"</code> is the | |
| 116 | only way for the user to activate that option. If the user asks for | |
| 117 | help, the help message will reflect that: | |
| 118 | <div class="verbatim"><pre> | |
| 119 | options: | |
| 120 | --dry-run do no harm | |
| 121 | [...] | |
| 122 | -n, --noisy be noisy | |
| 123 | </pre></div> | |
| 124 | ||
| 125 | <P> | |
| 126 | It's possible to whittle away the option strings for a previously-added | |
| 127 | option until there are none left, and the user has no way of invoking | |
| 128 | that option from the command-line. In that case, <tt class="module">optparse</tt> removes that | |
| 129 | option completely, so it doesn't show up in help text or anywhere else. | |
| 130 | Carrying on with our existing OptionParser: | |
| 131 | <div class="verbatim"><pre> | |
| 132 | parser.add_option("--dry-run", ..., help="new dry-run option") | |
| 133 | </pre></div> | |
| 134 | ||
| 135 | <P> | |
| 136 | At this point, the original <b class="programopt">-n/-dry-run</b> option is no longer | |
| 137 | accessible, so <tt class="module">optparse</tt> removes it, leaving this help text: | |
| 138 | <div class="verbatim"><pre> | |
| 139 | options: | |
| 140 | [...] | |
| 141 | -n, --noisy be noisy | |
| 142 | --dry-run new dry-run option | |
| 143 | </pre></div> | |
| 144 | ||
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