<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"><span class="pre">Validator</span></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"><span class="pre">None</span></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"><span class="pre">validate.py</span></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"><span class="pre">Validator</span></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>
<li><p class="first"><a class="reference external" href="http://www.voidspace.org.uk/cgi-bin/voidspace/downman.py?file=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://svn.pythonutils.python-hosting.com/trunk/pythonutils/">Subversion Repository</a>.</p>
<p><a class="reference external" href="http://www.voidspace.org.uk/python/validate.html">Validate</a> is also part of the <a class="reference external" href="http://www.voidspace.org.uk/python/pythonutils.html">Pythonutils</a> set of modules. This contains
various other useful helper modules, and is required by many of the <a class="reference external" href="http://www.voidspace.org.uk/python">Voidspace
Python Projects</a>.</p>
</div>
</div>
<div class="section" id="the-standard-functions">
<h1><a class="toc-backref" href="#id7">3 The standard functions</a></h1>
<p>The standard functions come built-in to every <tt class="docutils literal"><span class="pre">Validator</span></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>
<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">'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
</span><span class="pytext">vtor</span> <span class="pyoperator">=</span> <span class="pytext">Validator</span><span class="pyoperator">(</span><span class="pytext">fdict</span><span class="pyoperator">)</span><span class="pytext"></span></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"><span class="pre">vtor.functions</span></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
<span class="pytext">vtor</span><span class="pyoperator">.</span><span class="pytext">functions</span><span class="pyoperator">[</span><span class="pystring">'check_name3'</span><span class="pyoperator">]</span> <span class="pyoperator">=</span> <span class="pytext">function3</span><span class="pytext"></span></div><p><tt class="docutils literal"><span class="pre">vtor.functions</span></tt> is just a dictionary that maps names to functions, so we
could also have called <tt class="docutils literal"><span class="pre">vtor.functions.update(fdict)</span></tt>.</p>
</div>
<div class="section" id="writing-the-check">
<h2><a class="toc-backref" href="#id11">4.3 Writing the check</a></h2>
<p>As we've heard, the checks map to the names in the <tt class="docutils literal"><span class="pre">functions</span></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"><span class="pre">Validator</span></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="#id12">4.4 The check method</a></h2>
<p>If you're not using <tt class="docutils literal"><span class="pre">Validator</span></tt> from ConfigObj, then you'll need to call the
<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"><span class="pre">missing=True</span></tt> to the <tt class="docutils literal"><span class="pre">check</span></tt> method, as
well as a <tt class="docutils literal"><span class="pre">default=value</span></tt> in the check. (Constructing these checks is done
automatically by ConfigObj: you only need to know about the <tt class="docutils literal"><span class="pre">default=value</span></tt>
<span class="pykeyword">assert</span> <span class="pytext">vtor</span><span class="pyoperator">.</span><span class="pytext">check</span><span class="pyoperator">(</span><span class="pytext">check2</span><span class="pyoperator">,</span> <span class="pystring">''</span><span class="pyoperator">,</span> <span class="pytext">missing</span><span class="pyoperator">=</span><span class="pytext">True</span><span class="pyoperator">)</span> <span class="pyoperator">==</span> <span class="pystring">"val 1"</span><span class="pytext"></span></div><p>If you pass in <tt class="docutils literal"><span class="pre">missing=True</span></tt> to the check method, then the actual value is
ignored. If no default is specified in the check, a <tt class="docutils literal"><span class="pre">ValidateMissingValue</span></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"><span class="pre">default=None</span></tt> (case sensitive) then <tt class="docutils literal"><span class="pre">vtor.check</span></tt> will
<em>always</em> return <tt class="docutils literal"><span class="pre">None</span></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"><span class="pre">None</span></tt>) then it will be interpreted as the string <tt class="docutils literal"><span class="pre">'None'</span></tt>.</p>
</div>
</div>
<div class="section" id="list-values">
<h3><a class="toc-backref" href="#id14">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"><span class="pre">default</span></tt> value.
<p><tt class="docutils literal"><span class="pre">Validator</span></tt> instances have a <tt class="docutils literal"><span class="pre">get_default_value</span></tt> method. It takes a <tt class="docutils literal"><span class="pre">check</span></tt> string
(the same string you would pass to the <tt class="docutils literal"><span class="pre">check</span></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"><span class="pre">KeyError</span></tt>.</p>
<p>If the <tt class="docutils literal"><span class="pre">check</span></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>
<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"><span class="pre">vtor.check</span></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"><span class="pre">ValidateError</span></tt>. All errors (except for <tt class="docutils literal"><span class="pre">VdtParamError</span></tt>)
raised are sub-classes of this.</p>
<p>If an unrecognised check is specified then <tt class="docutils literal"><span class="pre">VdtUnknownCheckError</span></tt> is
raised.</p>
<p>There are also <tt class="docutils literal"><span class="pre">VdtTypeError</span></tt> and <tt class="docutils literal"><span class="pre">VdtValueError</span></tt>.</p>
<p>If incorrect parameters are passed to a check function then it will (or should)
raise <tt class="docutils literal"><span class="pre">VdtParamError</span></tt>. As this indicates <em>programmer</em> error, rather than an error
in the value, it is a subclass of <tt class="docutils literal"><span class="pre">SyntaxError</span></tt> instead of <tt class="docutils literal"><span class="pre">ValidateError</span></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"><span class="pre">VdtTypeError</span></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"><span class="pre">VdtValueError</span></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"><span class="pre">VdtTypeError</span></tt> and <tt class="docutils literal"><span class="pre">VdtValueError</span></tt> are initialised with the
incorrect value. In other words you raise them like this :</p>
</span><span class="pykeyword">raise</span> <span class="pytext">VdtValueError</span><span class="pyoperator">(</span><span class="pytext">value</span><span class="pyoperator">)</span><span class="pytext"></span></div><p><tt class="docutils literal"><span class="pre">VdtValueError</span></tt> has the following subclasses, which should be raised if
<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"><span class="pre">VdtParamError</span></tt>.</p>
<p>Next we check that the value is a list. Anything else should raise a
<tt class="docutils literal"><span class="pre">VdtTypeError</span></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"><span class="pre">VdtValueTooShortError</span></tt> or a <tt class="docutils literal"><span class="pre">VdtValueTooLongError</span></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"><span class="pre">VdtTypeError</span></tt>, any other value is a
<tt class="docutils literal"><span class="pre">VdtValueError</span></tt> (either too big, or too small).</p>
</span> <span class="pycomment"># if we got this far, all is well<br />
</span> <span class="pycomment"># return the new list<br />
</span> <span class="pykeyword">return</span> <span class="pytext">out</span><span class="pytext"></span></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"><span class="pre">VdtValueError</span></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"><span class="pre">ValidateError</span></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"><span class="pre">VdtTypeError</span></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"><span class="pre">ValidateError</span></tt>, that convey more specific information.</p>
</div>
</div>
<div class="section" id="known-issues">
<h1><a class="toc-backref" href="#id19">7 Known Issues</a></h1>
<p>The following parses and then blows up. The resulting error message
<li>A timestamp check function ? (Using the <tt class="docutils literal"><span class="pre">parse</span></tt> function from <tt class="docutils literal"><span class="pre">DateUtil</span></tt> perhaps).</li>
<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
<h2><a class="toc-backref" href="#id23">10.1 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">10.2 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">10.3 2008/02/05 - Version 0.3.0</a></h2>
<p>Improved performance with a parse cache.</p>
<p>New <tt class="docutils literal"><span class="pre">get_default_value</span></tt> method. Given a check it returns the default
value (converted to the correct type) or raises a <tt class="docutils literal"><span class="pre">KeyError</span></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">10.4 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">10.5 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"><span class="pre">boolean</span></tt> instead of <tt class="docutils literal"><span class="pre">bool</span></tt>; changed the
<tt class="docutils literal"><span class="pre">is_bool</span></tt> function to <tt class="docutils literal"><span class="pre">is_boolean</span></tt> (Sourceforge bug #1531525).</p>
</div>
<div class="section" id="version-0-2-2">
<h2><a class="toc-backref" href="#id28">10.6 2006/04/29 Version 0.2.2</a></h2>
<p>Addressed bug where a string would pass the <tt class="docutils literal"><span class="pre">is_list</span></tt> test. (Thanks to
Konrad Wojas.)</p>
</div>
<div class="section" id="version-0-2-1">
<h2><a class="toc-backref" href="#id29">10.7 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
