Form Variable Types and Typechecking

Created by . Last modified on 2003/08/01.

Most of this information was stolen from the old Trinkets Tutorial by Jim Fulton (Digital Creations), which will probably disappear when the old Zope.org site is no more, so I'm preserving some still relevant sections here for posterity.

Form variable types

Normally, Zope copies values from form fields as strings. Zope can be told to perform type conversions automatically by including type information in form variable names.

In the form generated by the downloadForm method, the input tag for the hidden field, secret, has a name attribute of secret:int. The :int part of the name indicates to Zope that the field should be converted to an integer before passing it to the published method.

Currently supported type conversions

Type	Python Object Passed
float	Float
int	Integer
long	Long integer
string	String
required	Non-blank string
text	String with carriage-return newline pairs converted to newlines.
lines	List of values separated by newlines.
tokens	List of values entered as multiple space-separated tokens in a single field.
date	Date Time instance
list	List
tuple	Tuple
record	Record
ignore_empty	Ignore empty
default	default
records	List of records

Examples of some supported types

RECORD

<INPUT TYPE="text" NAME="person.name:record" SIZE="30">

The input tag for the name field is named person.name:record. The :record part of the name indicates to Zope that the field should be converted to a record before passing it to the published method. A record variable will be created called person and it will have an attribute called name.

IGNORE_EMPTY

<INPUT TYPE="text" NAME="person.email:record:ignore_empty" SIZE="30">

When the email form field is left blank, :ignore_empty skips over the variable rather than returning a null string as its value. When the record person is returned it will not have an attribute called email if the user did not enter one.

DEFAULT

<INPUT TYPE="hidden" NAME="person.toppings:record:list:default" VALUE="All">
<select multiple NAME = "person.toppings:record:list:ignore_empty">
<option>Bacon</option>
<option>Cheese</option>
<option>Tomato</option>
<option>Pepper</option>
<option>Egg<option>
</select>

The default type allows a specified value to be inserted when the form field is left blank. In the above example, if the user does not select values from the list of toppings, the default value will be used. The record person will have the attribute toppings and its value will be the list containing the word All (if the field is empty) or a list containing the selected toppings.

RECORDS

<P><H2>Member #1<H2></P><BR>
<P>Please enter your name:<BR>
<INPUT TYPE="text" NAME="member.name:records:ignore_empty" SIZE="30"><BR>
your email:<BR>
<INPUT TYPE="text" NAME="member.email:records:ignore_empty" SIZE="30"><BR>
your age:<BR>
<INPUT TYPE="hidden" NAME="member.age:int:records:default" Value="0"<BR>
<INPUT TYPE="text" NAME="member.age:int:records:ignore_empty"></P><BR>


<P><H2>Member #2</H2></P><BR>
<P>Please enter your name:<BR>
<INPUT TYPE="text" NAME="member.name:records:ignore_empty" SIZE="30"><BR>
your email:<BR>
<INPUT TYPE="text" NAME="member.email:records:ignore_empty" SIZE="30"><BR>
your age:<BR>
<INPUT TYPE="text" NAME="member.age:int:records:ignore_empty"><BR>
</P>

In this sample the form asks for a name and age for two different members of a club. The :records part appears in each input tag. This type will create a list called members that will hold records (in this case it will hold two records). Each record can have the attributes name, email and age.

Note:

Before creating a second record and adding an attribute, Zope gets the last record in the list and checks to see if that record has the attribute. If the first record doesn't have the attribute, it inserts the attribute and value instead of creating a new record. For example, if the user entered a name and age for Member #1 and only an email for Member #2, the list will have only one record. That record will contain the name and age attribute from Member #1 as well as the email attribute from Member #2.

Type checking

If a value entered in a form does not match a type specification, or if a form value is omitted, Zope automatically generates an error response. This frees the programmer from writing some error checking code. Note that as of Zope 2.0.1, this error response is your standard Zope error/traceback screen, so I wouldn't recommend using it to enforce numeric or date types unless you combine it with fancy JavaScript or just don't care.