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HTTP Form Data Parser

Project description

zope.httpform is a library that, given a WSGI or CGI environment dictionary, will return a dictionary back containing converted form/query string elements. The form and query string elements contained in the environment are converted into simple Python types when the form element names are decorated with special suffixes. For example, in an HTML form that you’d like this library to process, you might say:

<form action=".">
   Age : <input type="hidden" name="age:int" value="20"/>
   <input type="submit" name="Submit"/>

Likewise, in the query string of the URL, you could put:

In both of these cases, when provided the WSGI or CGI environment, and asked to return a value, this library will return a dictionary like so:


This functionality has lived for a long time inside Zope’s publisher, but now it has been factored into this small library, making it easier to explain, test, and use.

Form/Query String Element Parsing

zope.httpform provides a way for you to specify form input types in the form, rather than in your application code. Instead of converting the age variable to an integer in a controller or view, you can indicate that it is an integer in the form itself:

Age <input type="text" name="age:int" />

The :int appended to the form input name tells this library to convert the form input to an integer when it is invoked. If the user of your form types something that cannot be converted to an integer in the above case (such as “22 going on 23”) then this library will raise a ValueError.

Here is a list of the standard parameter converters.


Converts a variable to true or false. Empty strings are evaluated as false and non-empty strings are evaluated as true.


Converts a variable to an integer.


Converts a variable to a long integer.


Converts a variable to a floating point number.


Converts a variable to a string. Most variables are strings already, so this converter is not often used except to simplify file uploads.


Converts a variable to a string with normalized line breaks. Different browsers on various platforms encode line endings differently, so this script makes sure the line endings are consistent, regardless of how they were encoded by the browser.


Converts a variable to a Python list.


Converts a variable to a Python tuple.


Converts a string to a list by breaking it on white spaces.


Converts a string to a list by breaking it on new lines.


Raises an exception if the variable is not present.


Excludes the variable from the form data if the variable is an empty string.

These converters all work in more or less the same way to coerce a form variable, which is a string, into another specific type.

The :list and :tuple converters can be used in combination with other converters. This allows you to apply additional converters to each element of the list or tuple. Consider this form:

<form action=".">

  <p>I like the following numbers</p>

  <input type="checkbox" name="favorite_numbers:list:int"
  value="1" /> One<br />

  <input type="checkbox" name="favorite_numbers:list:int"
  value="2" />Two<br />

  <input type="checkbox" name="favorite_numbers:list:int"
  value="3" />Three<br />

  <input type="checkbox" name="favorite_numbers:list:int"
  value="4" />Four<br />

  <input type="checkbox" name="favorite_numbers:list:int"
  value="5" />5<br />

  <input type="submit" />

By using the :list and :int converters together, this library will convert each selected item to an integer and then combine all selected integers into a list named favorite_numbers.

A more complex type of form conversion is to convert a series of inputs into records. Records are structures that have attributes. Using records, you can combine a number of form inputs into one variable with attributes. The available record converters are:


Converts a variable to a record attribute.


Converts a variable to a record attribute in a list of records.


Provides a default value for a record attribute if the variable is empty.


Skips a record attribute if the variable is empty.

Here are some examples of how these converters are used:

<form action=".">

  First Name <input type="text" name="person.fname:record" /><br />
  Last Name <input type="text" name="person.lname:record" /><br />
  Age <input type="text" name="person.age:record:int" /><br />

  <input type="submit" />

If the information represented by this form post is passed to zope.httpform, the resulting dictionary will container one parameter, person. The person variable will have the attributes fname, lname and age. Here’s an example of how you might use zope.httpform to process the form post (assuming you have a WSGI or CGI environment in hand):

from zope.httpform import parse

info = parse(environ, environ['wsgi.input'])
person = info['person']
full_name = "%s %s" % (person.fname, person.lname)
if person.age < 21:
    return ("Sorry, %s. You are not old enough to adopt an "
            "aardvark." % full_name)
return "Thanks, %s. Your aardvark is on its way." % full_name

The records converter works like the record converter except that it produces a list of records, rather than just one. Here is an example form:

<form action=".">

  <p>Please, enter information about one or more of your next of

    First Name <input type="text" name="people.fname:records" />
    Last Name <input type="text" name="people.lname:records" />

    First Name <input type="text" name="people.fname:records" />
    Last Name <input type="text" name="people.lname:records" />

    First Name <input type="text" name="people.fname:records" />
    Last Name <input type="text" name="people.lname:records" />

  <input type="submit" />

If you call zope.httpform’s parse method with the information from this form post, a dictionary will be returned from it with a variable called people that is a list of records. Each record will have fname and lname attributes. Note the difference between the records converter and the list:record converter: the former would create a list of records, whereas the latter would produce a single record whose attributes fname and lname would each be a list of values.

The order of combined modifiers does not matter; for example, :int:list is identical to :list:int.


The file pointer passed to zope.httpform.parse() will be consumed. For all intents and purposes this means you should make a tempfile copy of the wsgi.input file pointer before calling parse() if you intend to use the POST file input data in your application.


This documentation was graciously donated by the team at Agendaless Consulting. The zope.httpform package is expected to replace the repoze.monty package.

Version 1.0.2 (2009-07-24)

  • Include package data in release.
  • Default to UTF-8 decoding
  • Fixed a test failure on Python 2.6

Version 1.0.1 (2009-02-07)

  • Fixed some misleading documentation.
  • Relaxed the requirement for REQUEST_METHOD because the zope.publisher tests do not set it.
  • Used documentation and design ideas from repoze.monty. Thanks, Chris and Agendaless.

Version 1.0.0 (2009-02-06)

  • First release of zope.httpform. Extracted from zope.publisher 3.5.5.

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