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<title>Validation Schema with validate.py</title>
<meta name="authors" content="Michael Foord Nicola Larosa Mark Andrews" />
<meta name="date" content="2010/01/09" />
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<div class="document" id="validation-schema-with-validate-py">
<h1 class="title">Validation Schema with validate.py</h1>
<h2 class="subtitle" id="using-the-validator-class">Using the Validator class</h2>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr><th class="docinfo-name">Authors:</th>
<td>Michael Foord
<br />Nicola Larosa
<br />Mark Andrews</td></tr>
<tr><th class="docinfo-name">Version:</th>
<td>Validate 1.0.1</td></tr>
<tr><th class="docinfo-name">Date:</th>
<td>2010/01/09</td></tr>
<tr class="field"><th class="docinfo-name">Homepage:</th><td class="field-body"><a class="reference external" href="http://www.voidspace.org.uk/python/validate.html">Validate Homepage</a></td>
</tr>
<tr class="field"><th class="docinfo-name">Repository:</th><td class="field-body"><a class="reference external" href="http://code.google.com/p/configobj/">Google code homepage</a></td>
</tr>
<tr class="field"><th class="docinfo-name">PyPI Entry:</th><td class="field-body"><a class="reference external" href="http://pypi.python.org/pypi/validate">Validate on Python Packaging Index</a></td>
</tr>
<tr class="field"><th class="docinfo-name">License:</th><td class="field-body"><a class="reference external" href="http://www.voidspace.org.uk/python/license.shtml">BSD License</a></td>
</tr>
<tr class="field"><th class="docinfo-name">Support:</th><td class="field-body"><a class="reference external" href="http://lists.sourceforge.net/lists/listinfo/configobj-develop">Mailing List</a></td>
</tr>
</tbody>
</table>
<div class="contents topic" id="validate-manual">
<p class="topic-title first">Validate Manual</p>
<ul class="auto-toc simple">
<li><a class="reference internal" href="#introduction" id="id1">1 Introduction</a></li>
<li><a class="reference internal" href="#downloading" id="id2">2 Downloading</a><ul class="auto-toc">
<li><a class="reference internal" href="#files" id="id3">2.1 Files</a></li>
<li><a class="reference internal" href="#documentation" id="id4">2.2 Documentation</a></li>
</ul>
</li>
<li><a class="reference internal" href="#the-standard-functions" id="id5">3 The standard functions</a></li>
<li><a class="reference internal" href="#using-validator" id="id6">4 Using Validator</a><ul class="auto-toc">
<li><a class="reference internal" href="#instantiate" id="id7">4.1 Instantiate</a></li>
<li><a class="reference internal" href="#adding-functions" id="id8">4.2 Adding functions</a></li>
<li><a class="reference internal" href="#writing-the-check" id="id9">4.3 Writing the check</a></li>
<li><a class="reference internal" href="#the-check-method" id="id10">4.4 The check method</a><ul class="auto-toc">
<li><a class="reference internal" href="#default-values" id="id11">4.4.1 Default Values</a></li>
<li><a class="reference internal" href="#list-values" id="id12">4.4.2 List Values</a></li>
</ul>
</li>
<li><a class="reference internal" href="#get-default-value" id="id13">4.5 get_default_value</a></li>
</ul>
</li>
<li><a class="reference internal" href="#validator-exceptions" id="id14">5 Validator Exceptions</a></li>
<li><a class="reference internal" href="#writing-check-functions" id="id15">6 Writing check functions</a><ul class="auto-toc">
<li><a class="reference internal" href="#example" id="id16">6.1 Example</a></li>
</ul>
</li>
<li><a class="reference internal" href="#known-issues" id="id17">7 Known Issues</a></li>
<li><a class="reference internal" href="#todo" id="id18">8 TODO</a></li>
<li><a class="reference internal" href="#issues" id="id19">9 ISSUES</a></li>
<li><a class="reference internal" href="#changelog" id="id20">10 CHANGELOG</a><ul class="auto-toc">
<li><a class="reference internal" href="#version-1-0-1" id="id21">10.1 2009/10/25 - Version 1.0.1</a></li>
<li><a class="reference internal" href="#version-1-0-0" id="id22">10.2 2009/04/13 - Version 1.0.0</a></li>
<li><a class="reference internal" href="#version-0-3-2" id="id23">10.3 2008/02/24 - Version 0.3.2</a></li>
<li><a class="reference internal" href="#version-0-3-1" id="id24">10.4 2008/02/05 - Version 0.3.1</a></li>
<li><a class="reference internal" href="#version-0-3-0" id="id25">10.5 2008/02/05 - Version 0.3.0</a></li>
<li><a class="reference internal" href="#version-0-2-3" id="id26">10.6 2007/02/04 Version 0.2.3</a></li>
<li><a class="reference internal" href="#version-0-2-3-alpha1" id="id27">10.7 2006/12/17 Version 0.2.3-alpha1</a></li>
<li><a class="reference internal" href="#version-0-2-2" id="id28">10.8 2006/04/29 Version 0.2.2</a></li>
<li><a class="reference internal" href="#version-0-2-1" id="id29">10.9 2005/12/16 Version 0.2.1</a></li>
<li><a class="reference internal" href="#version-0-2-0" id="id30">10.10 2005/08/18 Version 0.2.0</a></li>
<li><a class="reference internal" href="#version-0-1-0" id="id31">10.11 2005/02/01 Version 0.1.0</a></li>
</ul>
</li>
</ul>
</div>
<div class="section" id="introduction">
<h1><a class="toc-backref" href="#id1">1 Introduction</a></h1>
<p>Validation is used to check that supplied values conform to a specification.</p>
<p>The value can be supplied as a string, e.g. from a config file. In this case
the check will also <em>convert</em> the value to the required type. This allows you
to add validation as a transparent layer to access data stored as strings. The
validation checks that the data is correct <em>and</em> converts it to the expected
type.</p>
<p>Checks are also strings, and are easy to write. One generic system can be used
to validate information from different sources via a single consistent
mechanism.</p>
<p>Checks look like function calls, and map to function calls. They can include
parameters and keyword arguments. These arguments are passed to the relevant
function by the <tt class="docutils literal">Validator</tt> instance, along with the value being checked.</p>
<p>The syntax for checks also allows for specifying a default value. This default
value can be <tt class="docutils literal">None</tt>, no matter what the type of the check. This can be used
to indicate that a value was missing, and so holds no useful value.</p>
<p>Functions either return a new value, or raise an exception. See <a class="reference internal" href="#validator-exceptions">Validator
Exceptions</a> for the low down on the exception classes that <tt class="docutils literal">validate.py</tt>
defines.</p>
<p>Some standard functions are provided, for basic data types; these come built
into every validator. Additional checks are easy to write: they can be provided
when the <tt class="docutils literal">Validator</tt> is instantiated, or added afterwards.</p>
<p>Validate was primarily written to support <a class="reference external" href="http://www.voidspace.org.uk/python/configobj.html">ConfigObj</a>, but is designed to be
applicable to many other situations.</p>
<p>For support and bug reports please use the ConfigObj <a class="reference external" href="http://lists.sourceforge.net/lists/listinfo/configobj-develop">Mailing List</a>.</p>
</div>
<div class="section" id="downloading">
<h1><a class="toc-backref" href="#id2">2 Downloading</a></h1>
<p>The current version is <strong>1.0.1</strong>, dated 9th January 2010.</p>
<p>You can get obtain validate in the following ways :</p>
<div class="section" id="files">
<h2><a class="toc-backref" href="#id3">2.1 Files</a></h2>
<ul>
<li><p class="first"><a class="reference external" href="http://www.voidspace.org.uk/cgi-bin/voidspace/download/validate.py">validate.py</a> from Voidspace</p>
</li>
<li><p class="first">configobj.zip from Voidspace - See the homepage of <a class="reference external" href="http://www.voidspace.org.uk/python/configobj.html">ConfigObj</a> for the latest
version and download links.</p>
<blockquote>
<p>This contains validate.py and <a class="reference external" href="http://www.voidspace.org.uk/python/validate.html">this document</a>. (As well as <a class="reference external" href="http://www.voidspace.org.uk/python/configobj.html">ConfigObj</a> and
the ConfigObj documentation).</p>
</blockquote>
</li>
<li><p class="first">The latest development version can be obtained from the <a class="reference external" href="http://code.google.com/p/configobj/">Subversion Repository</a>.</p>
</li>
</ul>
</div>
<div class="section" id="documentation">
<h2><a class="toc-backref" href="#id4">2.2 Documentation</a></h2>
<p><em>configobj.zip</em> contains <a class="reference external" href="http://www.voidspace.org.uk/python/validate.html">this document</a>.</p>
<ul class="simple">
<li>You can view <a class="reference external" href="http://www.voidspace.org.uk/python/validate.html">this document</a> online as the <a class="reference external" href="http://www.voidspace.org.uk/python/validate.html">Validate Homepage</a>.</li>
</ul>
</div>
</div>
<div class="section" id="the-standard-functions">
<h1><a class="toc-backref" href="#id5">3 The standard functions</a></h1>
<p>The standard functions come built-in to every <tt class="docutils literal">Validator</tt> instance. They work
with the following basic data types :</p>
<ul class="simple">
<li>integer</li>
<li>float</li>
<li>boolean</li>
<li>string</li>
<li>ip_addr</li>
</ul>
<p>plus lists of these datatypes.</p>
<p>Adding additional checks is done through coding simple functions.</p>
<p>The full set of standard checks are :</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">'integer':</th><td class="field-body"><p class="first">matches integer values (including negative). Takes optional 'min'
and 'max' arguments:</p>
<pre class="literal-block">
integer()
integer(3, 9) # any value from 3 to 9
integer(min=0) # any positive value
integer(max=9)
</pre>
</td>
</tr>
<tr class="field"><th class="field-name">'float':</th><td class="field-body"><p class="first">matches float values
Has the same parameters as the integer check.</p>
</td>
</tr>
<tr class="field"><th class="field-name">'boolean':</th><td class="field-body"><dl class="first docutils">
<dt>matches boolean values: <tt class="docutils literal">True</tt> or <tt class="docutils literal">False</tt>.</dt>
<dd><p class="first">Acceptable string values for True are:</p>
<pre class="last literal-block">
true, on, yes, 1
</pre>
</dd>
</dl>
<p>Acceptable string values for False are:</p>
<pre class="literal-block">
false, off, no, 0
</pre>
<p>Any other value raises an error.</p>
</td>
</tr>
<tr class="field"><th class="field-name">'string':</th><td class="field-body"><p class="first">matches any string. Takes optional keyword args 'min' and 'max' to
specify min and max length of string.</p>
</td>
</tr>
<tr class="field"><th class="field-name">'ip_addr':</th><td class="field-body"><p class="first">matches an Internet Protocol address, v.4, represented by a
dotted-quad string, i.e. '1.2.3.4'.</p>
</td>
</tr>
<tr class="field"><th class="field-name">'list':</th><td class="field-body"><p class="first">matches any list. Takes optional keyword args 'min', and 'max' to
specify min and max sizes of the list. The list checks always
return a list.</p>
</td>
</tr>
<tr class="field"><th class="field-name">force_list:</th><td class="field-body"><p class="first">matches any list, but if a single value is passed in will
coerce it into a list containing that value. Useful for
configobj if the user forgot the trailing comma to turn
a single value into a list.</p>
</td>
</tr>
<tr class="field"><th class="field-name">'tuple':</th><td class="field-body"><p class="first">matches any list. This check returns a tuple rather than a list.</p>
</td>
</tr>
<tr class="field"><th class="field-name">'int_list':</th><td class="field-body"><p class="first">Matches a list of integers. Takes the same arguments as list.</p>
</td>
</tr>
<tr class="field"><th class="field-name">'float_list':</th><td class="field-body"><p class="first">Matches a list of floats. Takes the same arguments as list.</p>
</td>
</tr>
<tr class="field"><th class="field-name">'bool_list':</th><td class="field-body"><p class="first">Matches a list of boolean values. Takes the same arguments as
list.</p>
</td>
</tr>
<tr class="field"><th class="field-name">'string_list':</th><td class="field-body"><p class="first">Matches a list of strings. Takes the same arguments as list.</p>
</td>
</tr>
<tr class="field"><th class="field-name">'ip_addr_list':</th><td class="field-body"><p class="first">Matches a list of IP addresses. Takes the same arguments as
list.</p>
</td>
</tr>
<tr class="field"><th class="field-name">'mixed_list':</th><td class="field-body"><p class="first">Matches a list with different types in specific positions.
List size must match the number of arguments.</p>
<p>Each position can be one of:</p>
<pre class="literal-block">
int, str, boolean, float, ip_addr
</pre>
<p>So to specify a list with two strings followed by two integers,
you write the check as:</p>
<pre class="literal-block">
mixed_list(str, str, int, int)
</pre>
</td>
</tr>
<tr class="field"><th class="field-name">'pass':</th><td class="field-body"><p class="first">matches everything: it never fails and the value is unchanged. It is
also the default if no check is specified.</p>
</td>
</tr>
<tr class="field"><th class="field-name">'option':</th><td class="field-body"><p class="first">matches any from a list of options.
You specify this test with:</p>
<pre class="last literal-block">
option('option 1', 'option 2', 'option 3')
</pre>
</td>
</tr>
</tbody>
</table>
<p>The following code will work without you having to specifically add the
functions yourself.</p>
<div class="highlight"><pre><span class="kn">from</span> <span class="nn">validate</span> <span class="kn">import</span> <span class="n">Validator</span>
<span class="c">#</span>
<span class="n">vtor</span> <span class="o">=</span> <span class="n">Validator</span><span class="p">()</span>
<span class="n">newval1</span> <span class="o">=</span> <span class="n">vtor</span><span class="o">.</span><span class="n">check</span><span class="p">(</span><span class="s">'integer'</span><span class="p">,</span> <span class="n">value1</span><span class="p">)</span>
<span class="n">newval2</span> <span class="o">=</span> <span class="n">vtor</span><span class="o">.</span><span class="n">check</span><span class="p">(</span><span class="s">'boolean'</span><span class="p">,</span> <span class="n">value2</span><span class="p">)</span>
<span class="c"># etc ...</span>
</pre></div>
<div class="note">
<p class="first admonition-title">Note</p>
<p class="last">Of course, if these checks fail they raise exceptions. So you should wrap
them in <tt class="docutils literal"><span class="pre">try...except</span></tt> blocks. Better still, use ConfigObj for a higher
level interface.</p>
</div>
</div>
<div class="section" id="using-validator">
<h1><a class="toc-backref" href="#id6">4 Using Validator</a></h1>
<p>Using <tt class="docutils literal">Validator</tt> is very easy. It has one public attribute and one public
method.</p>
<p>Shown below are the different steps in using <tt class="docutils literal">Validator</tt>.</p>
<p>The only additional thing you need to know, is about <a class="reference internal" href="#writing-check-functions">Writing check
functions</a>.</p>
<div class="section" id="instantiate">
<h2><a class="toc-backref" href="#id7">4.1 Instantiate</a></h2>
<div class="highlight"><pre><span class="kn">from</span> <span class="nn">validate</span> <span class="kn">import</span> <span class="n">Validator</span>
<span class="n">vtor</span> <span class="o">=</span> <span class="n">Validator</span><span class="p">()</span>
</pre></div>
<p>or even :</p>
<div class="highlight"><pre><span class="kn">from</span> <span class="nn">validate</span> <span class="kn">import</span> <span class="n">Validator</span>
<span class="c">#</span>
<span class="n">fdict</span> <span class="o">=</span> <span class="p">{</span>
<span class="s">'check_name1'</span><span class="p">:</span> <span class="n">function1</span><span class="p">,</span>
<span class="s">'check_name2'</span><span class="p">:</span> <span class="n">function2</span><span class="p">,</span>
<span class="s">'check_name3'</span><span class="p">:</span> <span class="n">function3</span><span class="p">,</span>
<span class="p">}</span>
<span class="c">#</span>
<span class="n">vtor</span> <span class="o">=</span> <span class="n">Validator</span><span class="p">(</span><span class="n">fdict</span><span class="p">)</span>
</pre></div>
<p>The second method adds a set of your functions as soon as your validator is
created. They are stored in the <tt class="docutils literal">vtor.functions</tt> dictionary. The 'key' you
give them in this dictionary is the name you use in your checks (not the
original function name).</p>
<p>Dictionary keys/functions you pass in can override the built-in ones if you
want.</p>
</div>
<div class="section" id="adding-functions">
<h2><a class="toc-backref" href="#id8">4.2 Adding functions</a></h2>
<p>The code shown above, for adding functions on instantiation, has exactly the
same effect as the following code :</p>
<div class="highlight"><pre><span class="kn">from</span> <span class="nn">validate</span> <span class="kn">import</span> <span class="n">Validator</span>
<span class="c">#</span>
<span class="n">vtor</span> <span class="o">=</span> <span class="n">Validator</span><span class="p">()</span>
<span class="n">vtor</span><span class="o">.</span><span class="n">functions</span><span class="p">[</span><span class="s">'check_name1'</span><span class="p">]</span> <span class="o">=</span> <span class="n">function1</span>
<span class="n">vtor</span><span class="o">.</span><span class="n">functions</span><span class="p">[</span><span class="s">'check_name2'</span><span class="p">]</span> <span class="o">=</span> <span class="n">function2</span>
<span class="n">vtor</span><span class="o">.</span><span class="n">functions</span><span class="p">[</span><span class="s">'check_name3'</span><span class="p">]</span> <span class="o">=</span> <span class="n">function3</span>
</pre></div>
<p><tt class="docutils literal">vtor.functions</tt> is just a dictionary that maps names to functions, so we
could also have called <tt class="docutils literal">vtor.functions.update(fdict)</tt>.</p>
</div>
<div class="section" id="writing-the-check">
<h2><a class="toc-backref" href="#id9">4.3 Writing the check</a></h2>
<p>As we've heard, the checks map to the names in the <tt class="docutils literal">functions</tt> dictionary.
You've got a full list of <a class="reference internal" href="#the-standard-functions">The standard functions</a> and the arguments they
take.</p>
<p>If you're using <tt class="docutils literal">Validator</tt> from ConfigObj, then your checks will look like:</p>
<pre class="literal-block">
keyword = int_list(max=6)
</pre>
<p>but the check part will be identical .</p>
</div>
<div class="section" id="the-check-method">
<h2><a class="toc-backref" href="#id10">4.4 The check method</a></h2>
<p>If you're not using <tt class="docutils literal">Validator</tt> from ConfigObj, then you'll need to call the
<tt class="docutils literal">check</tt> method yourself.</p>
<p>If the check fails then it will raise an exception, so you'll want to trap
that. Here's the basic example :</p>
<div class="highlight"><pre><span class="kn">from</span> <span class="nn">validate</span> <span class="kn">import</span> <span class="n">Validator</span><span class="p">,</span> <span class="n">ValidateError</span>
<span class="c">#</span>
<span class="n">vtor</span> <span class="o">=</span> <span class="n">Validator</span><span class="p">()</span>
<span class="n">check</span> <span class="o">=</span> <span class="s">"integer(0, 9)"</span>
<span class="n">value</span> <span class="o">=</span> <span class="mi">3</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">newvalue</span> <span class="o">=</span> <span class="n">vtor</span><span class="o">.</span><span class="n">check</span><span class="p">(</span><span class="n">check</span><span class="p">,</span> <span class="n">value</span><span class="p">)</span>
<span class="k">except</span> <span class="n">ValidateError</span><span class="p">:</span>
<span class="k">print</span> <span class="s">'Check Failed.'</span>
<span class="k">else</span><span class="p">:</span>
<span class="k">print</span> <span class="s">'Check passed.'</span>
</pre></div>
<div class="caution">
<p class="first admonition-title">Caution!</p>
<p class="last">Although the value can be a string, if it represents a list it should
already have been turned into a list of strings.</p>
</div>
<div class="section" id="default-values">
<h3><a class="toc-backref" href="#id11">4.4.1 Default Values</a></h3>
<p>Some values may not be available, and you may want to be able to specify a
default as part of the check.</p>
<p>You do this by passing the keyword <tt class="docutils literal">missing=True</tt> to the <tt class="docutils literal">check</tt> method, as
well as a <tt class="docutils literal">default=value</tt> in the check. (Constructing these checks is done
automatically by ConfigObj: you only need to know about the <tt class="docutils literal">default=value</tt>
part) :</p>
<div class="highlight"><pre><span class="n">check1</span> <span class="o">=</span> <span class="s">'integer(default=50)'</span>
<span class="n">check2</span> <span class="o">=</span> <span class="s">'option("val 1", "val 2", "val 3", default="val 1")'</span>
<span class="k">assert</span> <span class="n">vtor</span><span class="o">.</span><span class="n">check</span><span class="p">(</span><span class="n">check1</span><span class="p">,</span> <span class="s">''</span><span class="p">,</span> <span class="n">missing</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span> <span class="o">==</span> <span class="mi">50</span>
<span class="k">assert</span> <span class="n">vtor</span><span class="o">.</span><span class="n">check</span><span class="p">(</span><span class="n">check2</span><span class="p">,</span> <span class="s">''</span><span class="p">,</span> <span class="n">missing</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span> <span class="o">==</span> <span class="s">"val 1"</span>
</pre></div>
<p>If you pass in <tt class="docutils literal">missing=True</tt> to the check method, then the actual value is
ignored. If no default is specified in the check, a <tt class="docutils literal">ValidateMissingValue</tt>
exception is raised. If a default is specified then that is passed to the
check instead.</p>
<p>If the check has <tt class="docutils literal">default=None</tt> (case sensitive) then <tt class="docutils literal">vtor.check</tt> will
<em>always</em> return <tt class="docutils literal">None</tt> (the object). This makes it easy to tell your program
that this check contains no useful value when missing, i.e. the value is
optional, and may be omitted without harm.</p>
<div class="note">
<p class="first admonition-title">Note</p>
<p class="last">As of version 0.3.0, if you specify <tt class="docutils literal"><span class="pre">default='None'</span></tt> (note the quote marks
around <tt class="docutils literal">None</tt>) then it will be interpreted as the string <tt class="docutils literal">'None'</tt>.</p>
</div>
</div>
<div class="section" id="list-values">
<h3><a class="toc-backref" href="#id12">4.4.2 List Values</a></h3>
<p>It's possible that you would like your default value to be a list. It's even
possible that you will write your own check functions - and would like to pass
them keyword arguments as lists from within the check.</p>
<p>To avoid confusing syntax with commas and quotes you use a list constructor to
specify that keyword arguments are lists. This includes the <tt class="docutils literal">default</tt> value.
This makes checks look something like:</p>
<pre class="literal-block">
checkname(default=list('val1', 'val2', 'val3'))
</pre>
</div>
</div>
<div class="section" id="get-default-value">
<h2><a class="toc-backref" href="#id13">4.5 get_default_value</a></h2>
<p><tt class="docutils literal">Validator</tt> instances have a <tt class="docutils literal">get_default_value</tt> method. It takes a <tt class="docutils literal">check</tt> string
(the same string you would pass to the <tt class="docutils literal">check</tt> method) and returns the default value,
converted to the right type. If the check doesn't define a default value then this method
raises a <tt class="docutils literal">KeyError</tt>.</p>
<p>If the <tt class="docutils literal">check</tt> has been seen before then it will have been parsed and cached already,
so this method is not expensive to call (however the conversion is done each time).</p>
</div>
</div>
<div class="section" id="validator-exceptions">
<h1><a class="toc-backref" href="#id14">5 Validator Exceptions</a></h1>
<div class="note">
<p class="first admonition-title">Note</p>
<p class="last">If you only use Validator through ConfigObj, it traps these Exceptions for
you. You will still need to know about them for writing your own check
functions.</p>
</div>
<p><tt class="docutils literal">vtor.check</tt> indicates that the check has failed by raising an exception.
The appropriate error should be raised in the check function.</p>
<p>The base error class is <tt class="docutils literal">ValidateError</tt>. All errors (except for <tt class="docutils literal">VdtParamError</tt>)
raised are sub-classes of this.</p>
<p>If an unrecognised check is specified then <tt class="docutils literal">VdtUnknownCheckError</tt> is
raised.</p>
<p>There are also <tt class="docutils literal">VdtTypeError</tt> and <tt class="docutils literal">VdtValueError</tt>.</p>
<p>If incorrect parameters are passed to a check function then it will (or should)
raise <tt class="docutils literal">VdtParamError</tt>. As this indicates <em>programmer</em> error, rather than an error
in the value, it is a subclass of <tt class="docutils literal">SyntaxError</tt> instead of <tt class="docutils literal">ValidateError</tt>.</p>
<div class="note">
<p class="first admonition-title">Note</p>
<p class="last">This means it <em>won't</em> be caught by ConfigObj - but propagated instead.</p>
</div>
<p>If the value supplied is the wrong type, then the check should raise
<tt class="docutils literal">VdtTypeError</tt>. e.g. the check requires the value to be an integer (or
representation of an integer) and something else was supplied.</p>
<p>If the value supplied is the right type, but an unacceptable value, then the
check should raise <tt class="docutils literal">VdtValueError</tt>. e.g. the check requires the value to
be an integer (or representation of an integer) less than ten and a higher
value was supplied.</p>
<p>Both <tt class="docutils literal">VdtTypeError</tt> and <tt class="docutils literal">VdtValueError</tt> are initialised with the
incorrect value. In other words you raise them like this :</p>
<div class="highlight"><pre><span class="k">raise</span> <span class="n">VdtTypeError</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
<span class="c">#</span>
<span class="k">raise</span> <span class="n">VdtValueError</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
</pre></div>
<p><tt class="docutils literal">VdtValueError</tt> has the following subclasses, which should be raised if
they are more appropriate.</p>
<ul class="simple">
<li><tt class="docutils literal">VdtValueTooSmallError</tt></li>
<li><tt class="docutils literal">VdtValueTooBigError</tt></li>
<li><tt class="docutils literal">VdtValueTooShortError</tt></li>
<li><tt class="docutils literal">VdtValueTooLongError</tt></li>
</ul>
</div>
<div class="section" id="writing-check-functions">
<h1><a class="toc-backref" href="#id15">6 Writing check functions</a></h1>
<p>Writing check functions is easy.</p>
<p>The check function will receive the value as its first argument, followed by
any other parameters and keyword arguments.</p>
<p>If the check fails, it should raise a <tt class="docutils literal">VdtTypeError</tt> or a
<tt class="docutils literal">VdtValueError</tt> (or an appropriate subclass).</p>
<p>All parameters and keyword arguments are <em>always</em> passed as strings. (Parsed
from the check string).</p>
<p>The value might be a string (or list of strings) and need
converting to the right type - alternatively it might already be a list of
integers. Our function needs to be able to handle either.</p>
<p>If the check passes then it should return the value (possibly converted to the
right type).</p>
<p>And that's it !</p>
<div class="section" id="example">
<h2><a class="toc-backref" href="#id16">6.1 Example</a></h2>
<p>Here is an example function that requires a list of integers. Each integer
must be between 0 and 99.</p>
<p>It takes a single argument specifying the length of the list. (Which allows us
to use the same check in more than one place). If the length can't be converted
to an integer then we need to raise <tt class="docutils literal">VdtParamError</tt>.</p>
<p>Next we check that the value is a list. Anything else should raise a
<tt class="docutils literal">VdtTypeError</tt>. The list should also have 'length' entries. If the list
has more or less entries then we will need to raise a
<tt class="docutils literal">VdtValueTooShortError</tt> or a <tt class="docutils literal">VdtValueTooLongError</tt>.</p>
<p>Then we need to check every entry in the list. Each entry should be an integer
between 0 and 99, or a string representation of an integer between 0 and 99.
Any other type is a <tt class="docutils literal">VdtTypeError</tt>, any other value is a
<tt class="docutils literal">VdtValueError</tt> (either too big, or too small).</p>
<div class="highlight"><pre><span class="k">def</span> <span class="nf">special_list</span><span class="p">(</span><span class="n">value</span><span class="p">,</span> <span class="n">length</span><span class="p">):</span>
<span class="sd">"""</span>
<span class="sd"> Check that the supplied value is a list of integers,</span>
<span class="sd"> with 'length' entries, and each entry between 0 and 99.</span>
<span class="sd"> """</span>
<span class="c"># length is supplied as a string</span>
<span class="c"># we need to convert it to an integer</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">length</span> <span class="o">=</span> <span class="nb">int</span><span class="p">(</span><span class="n">length</span><span class="p">)</span>
<span class="k">except</span> <span class="ne">ValueError</span><span class="p">:</span>
<span class="k">raise</span> <span class="n">VdtParamError</span><span class="p">(</span><span class="s">'length'</span><span class="p">,</span> <span class="n">length</span><span class="p">)</span>
<span class="c">#</span>
<span class="c"># Check the supplied value is a list</span>
<span class="k">if</span> <span class="ow">not</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">value</span><span class="p">,</span> <span class="nb">list</span><span class="p">):</span>
<span class="k">raise</span> <span class="n">VdtTypeError</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
<span class="c">#</span>
<span class="c"># check the length of the list is correct</span>
<span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">value</span><span class="p">)</span> <span class="o">></span> <span class="n">length</span><span class="p">:</span>
<span class="k">raise</span> <span class="n">VdtValueTooLongError</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
<span class="k">elif</span> <span class="nb">len</span><span class="p">(</span><span class="n">value</span><span class="p">)</span> <span class="o"><</span> <span class="n">length</span><span class="p">:</span>
<span class="k">raise</span> <span class="n">VdtValueTooShortError</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
<span class="c">#</span>
<span class="c"># Next, check every member in the list</span>
<span class="c"># converting strings as necessary</span>
<span class="n">out</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">for</span> <span class="n">entry</span> <span class="ow">in</span> <span class="n">value</span><span class="p">:</span>
<span class="k">if</span> <span class="ow">not</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">entry</span><span class="p">,</span> <span class="p">(</span><span class="nb">str</span><span class="p">,</span> <span class="nb">unicode</span><span class="p">,</span> <span class="nb">int</span><span class="p">)):</span>
<span class="c"># a value in the list</span>
<span class="c"># is neither an integer nor a string</span>
<span class="k">raise</span> <span class="n">VdtTypeError</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
<span class="k">elif</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">entry</span><span class="p">,</span> <span class="p">(</span><span class="nb">str</span><span class="p">,</span> <span class="nb">unicode</span><span class="p">)):</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">entry</span><span class="o">.</span><span class="n">isdigit</span><span class="p">():</span>
<span class="k">raise</span> <span class="n">VdtTypeError</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">entry</span> <span class="o">=</span> <span class="nb">int</span><span class="p">(</span><span class="n">entry</span><span class="p">)</span>
<span class="k">if</span> <span class="n">entry</span> <span class="o"><</span> <span class="mi">0</span><span class="p">:</span>
<span class="k">raise</span> <span class="n">VdtValueTooSmallError</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
<span class="k">elif</span> <span class="n">entry</span> <span class="o">></span> <span class="mi">99</span><span class="p">:</span>
<span class="k">raise</span> <span class="n">VdtValueTooBigError</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
<span class="n">out</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">entry</span><span class="p">)</span>
<span class="c">#</span>
<span class="c"># if we got this far, all is well</span>
<span class="c"># return the new list</span>
<span class="k">return</span> <span class="n">out</span>
</pre></div>
<p>If you are only using validate from ConfigObj then the error type (<em>TooBig</em>,
<em>TooSmall</em>, etc) is lost - so you may only want to raise <tt class="docutils literal">VdtValueError</tt>.</p>
<div class="caution">
<p class="first admonition-title">Caution!</p>
<p>If your function raises an exception that isn't a subclass of
<tt class="docutils literal">ValidateError</tt>, then ConfigObj won't trap it. This means validation will
fail.</p>
<p class="last">This is why our function starts by checking the type of the value. If we
are passed the wrong type (e.g. an integer rather than a list) we get a
<tt class="docutils literal">VdtTypeError</tt> rather than bombing out when we try to iterate over
the value.</p>
</div>
<p>If you are using validate in another circumstance you may want to create your
own subclasses of <tt class="docutils literal">ValidateError</tt> which convey more specific information.</p>
</div>
</div>
<div class="section" id="known-issues">
<h1><a class="toc-backref" href="#id17">7 Known Issues</a></h1>
<p>The following parses and then blows up. The resulting error message
is confusing:</p>
<blockquote>
<tt class="docutils literal">checkname(default=list(1, 2, 3, 4)</tt></blockquote>
<p>This is because it parses as: <tt class="docutils literal"><span class="pre">checkname(default="list(1",</span> 2, 3, 4)</tt>.
That isn't actually unreasonable, but the error message won't help you
work out what has happened.</p>
</div>
<div class="section" id="todo">
<h1><a class="toc-backref" href="#id18">8 TODO</a></h1>
<ul class="simple">
<li>A regex check function ?</li>
<li>A timestamp check function ? (Using the <tt class="docutils literal">parse</tt> function from <tt class="docutils literal">DateUtil</tt> perhaps).</li>
</ul>
</div>
<div class="section" id="issues">
<h1><a class="toc-backref" href="#id19">9 ISSUES</a></h1>
<div class="note">
<p class="first admonition-title">Note</p>
<p class="last">Please file any bug reports to <a class="reference external" href="mailto:fuzzyman%40voidspace.org.uk">Michael Foord</a> or the ConfigObj
<a class="reference external" href="http://lists.sourceforge.net/lists/listinfo/configobj-develop">Mailing List</a>.</p>
</div>
<p>If we could pull tuples out of arguments, it would be easier
to specify arguments for 'mixed_lists'.</p>
</div>
<div class="section" id="changelog">
<h1><a class="toc-backref" href="#id20">10 CHANGELOG</a></h1>
<div class="section" id="version-1-0-1">
<h2><a class="toc-backref" href="#id21">10.1 2009/10/25 - Version 1.0.1</a></h2>
<ul class="simple">
<li>BUGFIX: Fixed compatibility with Python 2.3.</li>
</ul>
</div>
<div class="section" id="version-1-0-0">
<h2><a class="toc-backref" href="#id22">10.2 2009/04/13 - Version 1.0.0</a></h2>
<ul class="simple">
<li>BUGFIX: can now handle multiline strings.</li>
<li>Addition of 'force_list' validation option.</li>
</ul>
<p>As the API is stable and there are no known bugs or outstanding feature requests I am marking this 1.0.</p>
</div>
<div class="section" id="version-0-3-2">
<h2><a class="toc-backref" href="#id23">10.3 2008/02/24 - Version 0.3.2</a></h2>
<p>BUGFIX: Handling of None as default value fixed.</p>
</div>
<div class="section" id="version-0-3-1">
<h2><a class="toc-backref" href="#id24">10.4 2008/02/05 - Version 0.3.1</a></h2>
<p>BUGFIX: Unicode checks no longer broken.</p>
</div>
<div class="section" id="version-0-3-0">
<h2><a class="toc-backref" href="#id25">10.5 2008/02/05 - Version 0.3.0</a></h2>
<p>Improved performance with a parse cache.</p>
<p>New <tt class="docutils literal">get_default_value</tt> method. Given a check it returns the default
value (converted to the correct type) or raises a <tt class="docutils literal">KeyError</tt> if the
check doesn't specify a default.</p>
<p>Added 'tuple' check and corresponding 'is_tuple' function (which always returns a tuple).</p>
<p>BUGFIX: A quoted 'None' as a default value is no longer treated as None,
but as the string 'None'.</p>
<p>BUGFIX: We weren't unquoting keyword arguments of length two, so an
empty string didn't work as a default.</p>
<p>BUGFIX: Strings no longer pass the 'is_list' check. Additionally, the
list checks always return lists.</p>
<p>A couple of documentation bug fixes.</p>
<p>Removed CHANGELOG from module.</p>
</div>
<div class="section" id="version-0-2-3">
<h2><a class="toc-backref" href="#id26">10.6 2007/02/04 Version 0.2.3</a></h2>
<p>Release of 0.2.3</p>
</div>
<div class="section" id="version-0-2-3-alpha1">
<h2><a class="toc-backref" href="#id27">10.7 2006/12/17 Version 0.2.3-alpha1</a></h2>
<p>By Nicola Larosa</p>
<p>Fixed validate doc to talk of <tt class="docutils literal">boolean</tt> instead of <tt class="docutils literal">bool</tt>; changed the
<tt class="docutils literal">is_bool</tt> function to <tt class="docutils literal">is_boolean</tt> (Sourceforge bug #1531525).</p>
</div>
<div class="section" id="version-0-2-2">
<h2><a class="toc-backref" href="#id28">10.8 2006/04/29 Version 0.2.2</a></h2>
<p>Addressed bug where a string would pass the <tt class="docutils literal">is_list</tt> test. (Thanks to
Konrad Wojas.)</p>
</div>
<div class="section" id="version-0-2-1">
<h2><a class="toc-backref" href="#id29">10.9 2005/12/16 Version 0.2.1</a></h2>
<p>Fixed bug so we can handle keyword argument values with commas.</p>
<p>We now use a list constructor for passing list values to keyword arguments
(including <tt class="docutils literal">default</tt>):</p>
<pre class="literal-block">
default=list("val", "val", "val")
</pre>
<p>Added the <tt class="docutils literal">_test</tt> test.</p>
<p>Moved a function call outside a try...except block.</p>
</div>
<div class="section" id="version-0-2-0">
<h2><a class="toc-backref" href="#id30">10.10 2005/08/18 Version 0.2.0</a></h2>
<p>Updated by <a class="reference external" href="mailto:fuzzyman%40voidspace.org.uk">Michael Foord</a> and <a class="reference external" href="mailto:nico%40teknico.net">Nicola Larosa</a></p>
<p>Does type conversion as well.</p>
</div>
<div class="section" id="version-0-1-0">
<h2><a class="toc-backref" href="#id31">10.11 2005/02/01 Version 0.1.0</a></h2>
<p>Initial version developed by <a class="reference external" href="mailto:fuzzyman%40voidspace.org.uk">Michael Foord</a>
and Mark Andrews.</p>
</div>
</div>
</div>
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