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| 55 | <H2><A NAME="SECTION0082120000000000000000"></A><A NAME="optparse-tutorial"></A> |
| 56 | <BR> |
| 57 | 6.21.2 Tutorial |
| 58 | </H2> |
| 59 | |
| 60 | <P> |
| 61 | While <tt class="module">optparse</tt> is quite flexible and powerful, it's also straightforward to |
| 62 | use in most cases. This section covers the code patterns that are |
| 63 | common to any <tt class="module">optparse</tt>-based program. |
| 64 | |
| 65 | <P> |
| 66 | First, you need to import the OptionParser class; then, early in the |
| 67 | main program, create an OptionParser instance: |
| 68 | <div class="verbatim"><pre> |
| 69 | from optparse import OptionParser |
| 70 | [...] |
| 71 | parser = OptionParser() |
| 72 | </pre></div> |
| 73 | |
| 74 | <P> |
| 75 | Then you can start defining options. The basic syntax is: |
| 76 | <div class="verbatim"><pre> |
| 77 | parser.add_option(opt_str, ..., |
| 78 | attr=value, ...) |
| 79 | </pre></div> |
| 80 | |
| 81 | <P> |
| 82 | Each option has one or more option strings, such as <code>"-f"</code> or |
| 83 | <code>"-file"</code>, and several option attributes that tell <tt class="module">optparse</tt> what to |
| 84 | expect and what to do when it encounters that option on the command |
| 85 | line. |
| 86 | |
| 87 | <P> |
| 88 | Typically, each option will have one short option string and one long |
| 89 | option string, e.g.: |
| 90 | <div class="verbatim"><pre> |
| 91 | parser.add_option("-f", "--file", ...) |
| 92 | </pre></div> |
| 93 | |
| 94 | <P> |
| 95 | You're free to define as many short option strings and as many long |
| 96 | option strings as you like (including zero), as long as there is at |
| 97 | least one option string overall. |
| 98 | |
| 99 | <P> |
| 100 | The option strings passed to <tt class="method">add_option()</tt> are effectively labels for |
| 101 | the option defined by that call. For brevity, we will frequently refer |
| 102 | to <em>encountering an option</em> on the command line; in reality, <tt class="module">optparse</tt> |
| 103 | encounters <em>option strings</em> and looks up options from them. |
| 104 | |
| 105 | <P> |
| 106 | Once all of your options are defined, instruct <tt class="module">optparse</tt> to parse your |
| 107 | program's command line: |
| 108 | <div class="verbatim"><pre> |
| 109 | (options, args) = parser.parse_args() |
| 110 | </pre></div> |
| 111 | |
| 112 | <P> |
| 113 | (If you like, you can pass a custom argument list to <tt class="method">parse_args()</tt>, |
| 114 | but that's rarely necessary: by default it uses <code>sys.argv[1:]</code>.) |
| 115 | |
| 116 | <P> |
| 117 | <tt class="method">parse_args()</tt> returns two values: |
| 118 | |
| 119 | <UL> |
| 120 | <LI> |
| 121 | <code>options</code>, an object containing values for all of your options--e.g. if <code>"-file"</code> takes a single string argument, then |
| 122 | <code>options.file</code> will be the filename supplied by the user, or |
| 123 | <code>None</code> if the user did not supply that option |
| 124 | |
| 125 | <P> |
| 126 | </LI> |
| 127 | <LI> |
| 128 | <code>args</code>, the list of positional arguments leftover after parsing |
| 129 | options |
| 130 | |
| 131 | <P> |
| 132 | </LI> |
| 133 | </UL> |
| 134 | |
| 135 | <P> |
| 136 | This tutorial section only covers the four most important option |
| 137 | attributes: <tt class="member">action</tt>, <tt class="member">type</tt>, <tt class="member">dest</tt> (destination), and <tt class="member">help</tt>. |
| 138 | Of these, <tt class="member">action</tt> is the most fundamental. |
| 139 | |
| 140 | <P> |
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| 145 | <A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a> |
| 146 | |
| 147 | <UL CLASS="ChildLinks"> |
| 148 | <LI><A href="optparse-understanding-option-actions.html">6.21.2.1 Understanding option actions</a> |
| 149 | <LI><A href="optparse-store-action.html">6.21.2.2 The store action</a> |
| 150 | <LI><A href="optparse-handling-boolean-options.html">6.21.2.3 Handling boolean (flag) options</a> |
| 151 | <LI><A href="optparse-other-actions.html">6.21.2.4 Other actions</a> |
| 152 | <LI><A href="optparse-default-values.html">6.21.2.5 Default values</a> |
| 153 | <LI><A href="optparse-generating-help.html">6.21.2.6 Generating help</a> |
| 154 | <LI><A href="optparse-printing-version-string.html">6.21.2.7 Printing a version string</a> |
| 155 | <LI><A href="optparse-how-optparse-handles-errors.html">6.21.2.8 How <tt class="module">optparse</tt> handles errors</a> |
| 156 | <LI><A href="optparse-putting-it-all-together.html">6.21.2.9 Putting it all together</a> |
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