| 1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> |
| 2 | <html> |
| 3 | <head> |
| 4 | <link rel="STYLESHEET" href="lib.css" type='text/css' /> |
| 5 | <link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" /> |
| 6 | <link rel='start' href='../index.html' title='Python Documentation Index' /> |
| 7 | <link rel="first" href="lib.html" title='Python Library Reference' /> |
| 8 | <link rel='contents' href='contents.html' title="Contents" /> |
| 9 | <link rel='index' href='genindex.html' title='Index' /> |
| 10 | <link rel='last' href='about.html' title='About this document...' /> |
| 11 | <link rel='help' href='about.html' title='About this document...' /> |
| 12 | <link rel="next" href="optparse-printing-version-string.html" /> |
| 13 | <link rel="prev" href="optparse-default-values.html" /> |
| 14 | <link rel="parent" href="optparse-tutorial.html" /> |
| 15 | <link rel="next" href="optparse-printing-version-string.html" /> |
| 16 | <meta name='aesop' content='information' /> |
| 17 | <title>6.21.2.6 Generating help</title> |
| 18 | </head> |
| 19 | <body> |
| 20 | <DIV CLASS="navigation"> |
| 21 | <div id='top-navigation-panel' xml:id='top-navigation-panel'> |
| 22 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> |
| 23 | <tr> |
| 24 | <td class='online-navigation'><a rel="prev" title="6.21.2.5 Default values" |
| 25 | href="optparse-default-values.html"><img src='../icons/previous.png' |
| 26 | border='0' height='32' alt='Previous Page' width='32' /></A></td> |
| 27 | <td class='online-navigation'><a rel="parent" title="6.21.2 Tutorial" |
| 28 | href="optparse-tutorial.html"><img src='../icons/up.png' |
| 29 | border='0' height='32' alt='Up One Level' width='32' /></A></td> |
| 30 | <td class='online-navigation'><a rel="next" title="6.21.2.7 Printing a version" |
| 31 | href="optparse-printing-version-string.html"><img src='../icons/next.png' |
| 32 | border='0' height='32' alt='Next Page' width='32' /></A></td> |
| 33 | <td align="center" width="100%">Python Library Reference</td> |
| 34 | <td class='online-navigation'><a rel="contents" title="Table of Contents" |
| 35 | href="contents.html"><img src='../icons/contents.png' |
| 36 | border='0' height='32' alt='Contents' width='32' /></A></td> |
| 37 | <td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png' |
| 38 | border='0' height='32' alt='Module Index' width='32' /></a></td> |
| 39 | <td class='online-navigation'><a rel="index" title="Index" |
| 40 | href="genindex.html"><img src='../icons/index.png' |
| 41 | border='0' height='32' alt='Index' width='32' /></A></td> |
| 42 | </tr></table> |
| 43 | <div class='online-navigation'> |
| 44 | <b class="navlabel">Previous:</b> |
| 45 | <a class="sectref" rel="prev" href="optparse-default-values.html">6.21.2.5 Default values</A> |
| 46 | <b class="navlabel">Up:</b> |
| 47 | <a class="sectref" rel="parent" href="optparse-tutorial.html">6.21.2 Tutorial</A> |
| 48 | <b class="navlabel">Next:</b> |
| 49 | <a class="sectref" rel="next" href="optparse-printing-version-string.html">6.21.2.7 Printing a version</A> |
| 50 | </div> |
| 51 | <hr /></div> |
| 52 | </DIV> |
| 53 | <!--End of Navigation Panel--> |
| 54 | |
| 55 | <H3><A NAME="SECTION0082126000000000000000"></A><A NAME="optparse-generating-help"></A> |
| 56 | <BR> |
| 57 | 6.21.2.6 Generating help |
| 58 | </H3> |
| 59 | |
| 60 | <P> |
| 61 | <tt class="module">optparse</tt>'s ability to generate help and usage text automatically is useful |
| 62 | for creating user-friendly command-line interfaces. All you have to do |
| 63 | is supply a <tt class="member">help</tt> value for each option, and optionally a short usage |
| 64 | message for your whole program. Here's an OptionParser populated with |
| 65 | user-friendly (documented) options: |
| 66 | <div class="verbatim"><pre> |
| 67 | usage = "usage: %prog [options] arg1 arg2" |
| 68 | parser = OptionParser(usage=usage) |
| 69 | parser.add_option("-v", "--verbose", |
| 70 | action="store_true", dest="verbose", default=True, |
| 71 | help="make lots of noise [default]") |
| 72 | parser.add_option("-q", "--quiet", |
| 73 | action="store_false", dest="verbose", |
| 74 | help="be vewwy quiet (I'm hunting wabbits)") |
| 75 | parser.add_option("-f", "--filename", |
| 76 | metavar="FILE", help="write output to FILE"), |
| 77 | parser.add_option("-m", "--mode", |
| 78 | default="intermediate", |
| 79 | help="interaction mode: novice, intermediate, " |
| 80 | "or expert [default: %default]") |
| 81 | </pre></div> |
| 82 | |
| 83 | <P> |
| 84 | If <tt class="module">optparse</tt> encounters either <code>"-h"</code> or <code>"-help"</code> on the command-line, |
| 85 | or if you just call <tt class="method">parser.print_help()</tt>, it prints the following to |
| 86 | standard output: |
| 87 | <div class="verbatim"><pre> |
| 88 | usage: <yourscript> [options] arg1 arg2 |
| 89 | |
| 90 | options: |
| 91 | -h, --help show this help message and exit |
| 92 | -v, --verbose make lots of noise [default] |
| 93 | -q, --quiet be vewwy quiet (I'm hunting wabbits) |
| 94 | -f FILE, --filename=FILE |
| 95 | write output to FILE |
| 96 | -m MODE, --mode=MODE interaction mode: novice, intermediate, or |
| 97 | expert [default: intermediate] |
| 98 | </pre></div> |
| 99 | |
| 100 | <P> |
| 101 | (If the help output is triggered by a help option, <tt class="module">optparse</tt> exits after |
| 102 | printing the help text.) |
| 103 | |
| 104 | <P> |
| 105 | There's a lot going on here to help <tt class="module">optparse</tt> generate the best possible |
| 106 | help message: |
| 107 | |
| 108 | <UL> |
| 109 | <LI> |
| 110 | the script defines its own usage message: |
| 111 | <div class="verbatim"><pre> |
| 112 | usage = "usage: %prog [options] arg1 arg2" |
| 113 | </pre></div> |
| 114 | |
| 115 | <P> |
| 116 | <tt class="module">optparse</tt> expands <code>"%prog"</code> in the usage string to the name of the current |
| 117 | program, i.e. <code>os.path.basename(sys.argv[0])</code>. The expanded string |
| 118 | is then printed before the detailed option help. |
| 119 | |
| 120 | <P> |
| 121 | If you don't supply a usage string, <tt class="module">optparse</tt> uses a bland but sensible |
| 122 | default: ``<code>usage: %prog [options]"</code>, which is fine if your script |
| 123 | doesn't take any positional arguments. |
| 124 | |
| 125 | <P> |
| 126 | </LI> |
| 127 | <LI> |
| 128 | every option defines a help string, and doesn't worry about line- |
| 129 | wrapping--<tt class="module">optparse</tt> takes care of wrapping lines and making the |
| 130 | help output look good. |
| 131 | |
| 132 | <P> |
| 133 | </LI> |
| 134 | <LI> |
| 135 | options that take a value indicate this fact in their |
| 136 | automatically-generated help message, e.g. for the ``mode'' option: |
| 137 | <div class="verbatim"><pre> |
| 138 | -m MODE, --mode=MODE |
| 139 | </pre></div> |
| 140 | |
| 141 | <P> |
| 142 | Here, ``MODE'' is called the meta-variable: it stands for the argument |
| 143 | that the user is expected to supply to <b class="programopt">-m</b>/<b class="programopt">--mode</b>. By default, |
| 144 | <tt class="module">optparse</tt> converts the destination variable name to uppercase and uses |
| 145 | that for the meta-variable. Sometimes, that's not what you want--for example, the <b class="programopt">--filename</b> option explicitly sets |
| 146 | <code>metavar="FILE"</code>, resulting in this automatically-generated option |
| 147 | description: |
| 148 | <div class="verbatim"><pre> |
| 149 | -f FILE, --filename=FILE |
| 150 | </pre></div> |
| 151 | |
| 152 | <P> |
| 153 | This is important for more than just saving space, though: the |
| 154 | manually written help text uses the meta-variable ``FILE'' to clue the |
| 155 | user in that there's a connection between the semi-formal syntax ``-f |
| 156 | FILE'' and the informal semantic description ``write output to FILE''. |
| 157 | This is a simple but effective way to make your help text a lot |
| 158 | clearer and more useful for end users. |
| 159 | |
| 160 | <P> |
| 161 | </LI> |
| 162 | <LI> |
| 163 | options that have a default value can include <code>%default</code> in |
| 164 | the help string--<tt class="module">optparse</tt> will replace it with <tt class="function">str()</tt> of the |
| 165 | option's default value. If an option has no default value (or the |
| 166 | default value is <code>None</code>), <code>%default</code> expands to <code>none</code>. |
| 167 | |
| 168 | <P> |
| 169 | </LI> |
| 170 | </UL> |
| 171 | |
| 172 | <P> |
| 173 | |
| 174 | <DIV CLASS="navigation"> |
| 175 | <div class='online-navigation'> |
| 176 | <p></p><hr /> |
| 177 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> |
| 178 | <tr> |
| 179 | <td class='online-navigation'><a rel="prev" title="6.21.2.5 Default values" |
| 180 | href="optparse-default-values.html"><img src='../icons/previous.png' |
| 181 | border='0' height='32' alt='Previous Page' width='32' /></A></td> |
| 182 | <td class='online-navigation'><a rel="parent" title="6.21.2 Tutorial" |
| 183 | href="optparse-tutorial.html"><img src='../icons/up.png' |
| 184 | border='0' height='32' alt='Up One Level' width='32' /></A></td> |
| 185 | <td class='online-navigation'><a rel="next" title="6.21.2.7 Printing a version" |
| 186 | href="optparse-printing-version-string.html"><img src='../icons/next.png' |
| 187 | border='0' height='32' alt='Next Page' width='32' /></A></td> |
| 188 | <td align="center" width="100%">Python Library Reference</td> |
| 189 | <td class='online-navigation'><a rel="contents" title="Table of Contents" |
| 190 | href="contents.html"><img src='../icons/contents.png' |
| 191 | border='0' height='32' alt='Contents' width='32' /></A></td> |
| 192 | <td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png' |
| 193 | border='0' height='32' alt='Module Index' width='32' /></a></td> |
| 194 | <td class='online-navigation'><a rel="index" title="Index" |
| 195 | href="genindex.html"><img src='../icons/index.png' |
| 196 | border='0' height='32' alt='Index' width='32' /></A></td> |
| 197 | </tr></table> |
| 198 | <div class='online-navigation'> |
| 199 | <b class="navlabel">Previous:</b> |
| 200 | <a class="sectref" rel="prev" href="optparse-default-values.html">6.21.2.5 Default values</A> |
| 201 | <b class="navlabel">Up:</b> |
| 202 | <a class="sectref" rel="parent" href="optparse-tutorial.html">6.21.2 Tutorial</A> |
| 203 | <b class="navlabel">Next:</b> |
| 204 | <a class="sectref" rel="next" href="optparse-printing-version-string.html">6.21.2.7 Printing a version</A> |
| 205 | </div> |
| 206 | </div> |
| 207 | <hr /> |
| 208 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> |
| 209 | </DIV> |
| 210 | <!--End of Navigation Panel--> |
| 211 | <ADDRESS> |
| 212 | See <i><a href="about.html">About this document...</a></i> for information on suggesting changes. |
| 213 | </ADDRESS> |
| 214 | </BODY> |
| 215 | </HTML> |