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| 55 | <H3><A NAME="SECTION0082151000000000000000"></A><A NAME="optparse-adding-new-types"></A> | |
| 56 | <BR> | |
| 57 | 6.21.5.1 Adding new types | |
| 58 | </H3> | |
| 59 | ||
| 60 | <P> | |
| 61 | To add new types, you need to define your own subclass of <tt class="module">optparse</tt>'s Option | |
| 62 | class. This class has a couple of attributes that define <tt class="module">optparse</tt>'s types: | |
| 63 | <tt class="member">TYPES</tt> and <tt class="member">TYPE_CHECKER</tt>. | |
| 64 | ||
| 65 | <P> | |
| 66 | <tt class="member">TYPES</tt> is a tuple of type names; in your subclass, simply define a new | |
| 67 | tuple <tt class="member">TYPES</tt> that builds on the standard one. | |
| 68 | ||
| 69 | <P> | |
| 70 | <tt class="member">TYPE_CHECKER</tt> is a dictionary mapping type names to type-checking | |
| 71 | functions. A type-checking function has the following signature: | |
| 72 | <div class="verbatim"><pre> | |
| 73 | def check_mytype(option, opt, value) | |
| 74 | </pre></div> | |
| 75 | ||
| 76 | <P> | |
| 77 | where <code>option</code> is an <tt class="class">Option</tt> instance, <code>opt</code> is an option string | |
| 78 | (e.g., <code>"-f"</code>), and <code>value</code> is the string from the command line that | |
| 79 | must be checked and converted to your desired type. <code>check_mytype()</code> | |
| 80 | should return an object of the hypothetical type <code>mytype</code>. The value | |
| 81 | returned by a type-checking function will wind up in the OptionValues | |
| 82 | instance returned by <tt class="method">OptionParser.parse_args()</tt>, or be passed to a | |
| 83 | callback as the <code>value</code> parameter. | |
| 84 | ||
| 85 | <P> | |
| 86 | Your type-checking function should raise OptionValueError if it | |
| 87 | encounters any problems. OptionValueError takes a single string | |
| 88 | argument, which is passed as-is to OptionParser's <tt class="method">error()</tt> method, | |
| 89 | which in turn prepends the program name and the string <code>"error:"</code> and | |
| 90 | prints everything to stderr before terminating the process. | |
| 91 | ||
| 92 | <P> | |
| 93 | Here's a silly example that demonstrates adding a <code>complex</code> option | |
| 94 | type to parse Python-style complex numbers on the command line. (This | |
| 95 | is even sillier than it used to be, because <tt class="module">optparse</tt> 1.3 added built-in | |
| 96 | support for complex numbers, but never mind.) | |
| 97 | ||
| 98 | <P> | |
| 99 | First, the necessary imports: | |
| 100 | <div class="verbatim"><pre> | |
| 101 | from copy import copy | |
| 102 | from optparse import Option, OptionValueError | |
| 103 | </pre></div> | |
| 104 | ||
| 105 | <P> | |
| 106 | You need to define your type-checker first, since it's referred to later | |
| 107 | (in the <tt class="member">TYPE_CHECKER</tt> class attribute of your Option subclass): | |
| 108 | <div class="verbatim"><pre> | |
| 109 | def check_complex(option, opt, value): | |
| 110 | try: | |
| 111 | return complex(value) | |
| 112 | except ValueError: | |
| 113 | raise OptionValueError( | |
| 114 | "option %s: invalid complex value: %r" % (opt, value)) | |
| 115 | </pre></div> | |
| 116 | ||
| 117 | <P> | |
| 118 | Finally, the Option subclass: | |
| 119 | <div class="verbatim"><pre> | |
| 120 | class MyOption (Option): | |
| 121 | TYPES = Option.TYPES + ("complex",) | |
| 122 | TYPE_CHECKER = copy(Option.TYPE_CHECKER) | |
| 123 | TYPE_CHECKER["complex"] = check_complex | |
| 124 | </pre></div> | |
| 125 | ||
| 126 | <P> | |
| 127 | (If we didn't make a <tt class="function">copy()</tt> of <tt class="member">Option.TYPE_CHECKER</tt>, we would end | |
| 128 | up modifying the <tt class="member">TYPE_CHECKER</tt> attribute of <tt class="module">optparse</tt>'s Option class. | |
| 129 | This being Python, nothing stops you from doing that except good manners | |
| 130 | and common sense.) | |
| 131 | ||
| 132 | <P> | |
| 133 | That's it! Now you can write a script that uses the new option type | |
| 134 | just like any other <tt class="module">optparse</tt>-based script, except you have to instruct your | |
| 135 | OptionParser to use MyOption instead of Option: | |
| 136 | <div class="verbatim"><pre> | |
| 137 | parser = OptionParser(option_class=MyOption) | |
| 138 | parser.add_option("-c", type="complex") | |
| 139 | </pre></div> | |
| 140 | ||
| 141 | <P> | |
| 142 | Alternately, you can build your own option list and pass it to | |
| 143 | OptionParser; if you don't use <tt class="method">add_option()</tt> in the above way, you | |
| 144 | don't need to tell OptionParser which option class to use: | |
| 145 | <div class="verbatim"><pre> | |
| 146 | option_list = [MyOption("-c", action="store", type="complex", dest="c")] | |
| 147 | parser = OptionParser(option_list=option_list) | |
| 148 | </pre></div> | |
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