Widget: the base class

Widget is the abstract base class for the widget hierarchy. It provides the following facilities:

• widget name (name attribute, set_name() method)
• widget value (value attribute, set_value() and clear() methods)
• __str__() and __repr__() methods
• some facilities for writing composite widget classes

The Widget constructor signature is:

Widget(name : string, value : any = None)

name

the name of the widget. For non-compound widgets (ie. everything in the above class hierarchy), this will be used as the "name" attribute for the main HTML tag that defines the form element.

value

the current value of the form element. The type of 'value' depends on the widget class. Most widget classes support only a single type, eg. StringWidget always deals with strings and IntWidget with integers. The SelectWidget classes are different; see the descriptions below for details.

Common widget methods

The Widget base class also provides a couple of useful methods:

set_value(value:any)

use this to set the widget value; this is the same as supplying a value to the constructor (and the same type rules apply, ie. the type of 'value' depends on the widget class).

The following two methods will be used on every widget object you create; if you write your own widget classes, you will almost certainly have to define both of these:

render() : string

return a chunk of HTML that implements the form element corresponding to this widget.

parse() : any

extract the form value for this widget from request.form, parse it according to the rules for this widget class, and return the resulting value. The return value depends on the widget class, and will be of the same type as the value passed to the constructor and/or set_value().

StringWidget

Used for short, single-line string input with no validation (ie. any string will be accepted.) Generates an <input type="text"> form element.

StringWidget(name : string,
             value : string = None,
             size : int = None,
             maxlength : int = None)

>>> StringWidget("foo", value="hello").render()
'<input name="foo" type="text" value="hello">'

>>> StringWidget("foo", size=10, maxlength=20).render()
'<input name="foo" type="text" size="10" maxlength="20">'

PasswordWidget

PasswordWidget is identical to StringWidget except for the type of the HTML form element: password instead of text.

TextWidget

Used for multi-line text input. The value is a single string with newlines right where the browser supplied them. (\r\n, if present, is converted to \n.) Generates a <textarea> form element.

TextWidget(name : string,
           value : string = None,
           cols : int = None,
           rows : int = None,
           wrap : string = "physical")

CheckboxWidget

Used for single boolean (on/off) value. The value you supply can be anything, since Python has a boolean interpretation for all values; the value returned by parse() will always be 0 or 1 (but you shouldn't rely on that!). Generates an <input type="checkbox"> form element.

CheckboxWidget(name : string,
               value : boolean = false)

>>> CheckboxWidget("foo", value=0).render()
'<input name="foo" type="checkbox" value="yes">'

>>> CheckboxWidget("foo", value="you bet").render()
'<input name="foo" type="checkbox" value="yes" checked>'

RadiobuttonsWidget

Used for a set of related radiobuttons, ie. several <input type="radio"> tags with the same name and different values. The set of values are supplied to the constructor as allowed_values, which may be a list of any Python objects (not just strings). The current value must be either None (the default) or one of the values in allowed_values; if you supply a value not in allowed_values, it will be ignored. parse() will return either None or one of the values in allowed_values.

RadiobuttonsWidget(name : string,
                   value : any = None,
                   allowed_values : [any] = None,
                   descriptions : [string] = map(str, allowed_values),
                   quote : boolean = true,
                   delim : string = "\n")

>>> colours = ["red", "green", "blue", "pink"]
>>> widget = RadiobuttonsWidget("foo", allowed_values=colours)
>>> print widget.render()
<input name="foo" type="radio" value="0">red</input>
<input name="foo" type="radio" value="1">green</input>
<input name="foo" type="radio" value="2">blue</input>
<input name="foo" type="radio" value="3">pink</input>

>>> values = [val1, val2, val3]
>>> descs = ["thing <b>1</b>",
             "thing <b>2</b>",
             "thing <b>3</b>"]
>>> widget = RadiobuttonsWidget("bar",
                 allowed_values=values,
                 descriptions=descs,
                 value=val3,
                 delim="<br>\n",
                 quote=0)
>>> print widget.render()
<input name="bar" type="radio" value="0">thing <b>1</b></input><br>
<input name="bar" type="radio" value="1">thing <b>2</b></input><br>
<input name="bar" type="radio" value="2" checked="checked">thing <b>3</b></input>

SingleSelectWidget

Used to select a single value from a list that's too long or ungainly for a set of radiobuttons. (Most browsers implement this as a scrolling list; UNIX versions of Netscape 4.x and earlier used a pop-up menu.) The value can be any Python object; parse() will return either None or one of the values you supply to the constructor as allowed_values. Generates a <select>...</select> tag, with one <option> tag for each element of allowed_values.

SingleSelectWidget(name : string,
                   value : any = None,
                   allowed_values : [any] = None,
                   descriptions : [string] = map(str, allowed_values),
                   quote : boolean = true,
                   size : int = None)

>>> widget = SingleSelectWidget("foo",
                                allowed_values=["abc", 123, 5.5])
>>> print widget.render()
<select name="foo">
<option value="0">abc
<option value="1">123
<option value="2">5.5
</select>

>>> widget = SingleSelectWidget("bar",
                                value=val2,
                                allowed_values=[val1, val2, val3],
                                descriptions=["foo", "bar", "foo & bar"],
                                size=3)
>>> print widget.render()
<select name="bar" size="3">
<option value="0">foo
<option selected value="1">bar
<option value="2">foo &amp; bar
</select>

MultipleSelectWidget

Used to select multiple values from a list. Everything is just like SingleSelectWidget, except that value can be a list of objects selected from allowed_values (in which case every object in value will initially be selected). Generates a <select multiple>...</select> tag, with one <option> tag for each element of allowed_values.

MultipleSelectWidget(name : string,
                     value : any | [any] = None,
                     allowed_values : [any] = None,
                     descriptions : [string] = map(str, allowed_values),
                     quote : boolean = true,
                     size : int = None)

ButtonWidget

Base class of SubmitWidget and ResetWidget. A ButtonWidget does nothing except create a button on the page.

>>> ButtonWidget("button", value="hello").render()
'<input type="button" name="button" value="hello">'

SubmitWidget

Used for generating submit buttons. Note that HTML submit buttons are rather weird, and Quixote preserves this weirdness -- the Widget classes are meant to be a fairly thin wrapper around HTML form elements, after all.

In particular, the widget value for a submit button controls two things: what the user sees in their browser (the text in the button) and what the browser returns as the value for that form element. You can't control the two separately, as you can with radiobuttons or selection widgets.

SubmitButtonWidget(name : string = None,
                   value : string = None)

ResetWidget

Generates a button to reset the form:

>>> ResetWidget("reset").render()
'<input type="reset" name="reset">'

HiddenWidget

Used to generate HTML hidden widgets, which can be useful for carrying around non-sensitive application state. (The Quixote form framework uses hidden widgets for form tokens as a measure against cross-site request forgery [CSRF] attacks. So by "sensitive" I mean "information which should not be revealed", rather than "security-related". If you wouldn't put it in a cookie or in email, don't put it in a hidden form element.)

HiddenWidget(name : string,
             value : string)

>>> HiddenWidget("form_id", "2452345135").render()
'<input type="hidden" name="form_id" value="2452345135">'

IntWidget

The first derived widget class: this is a subclass of StringWidget specifically for entering integer values. As such, this is the first widget class we've covered that can reject certain user input. (The selection widgets all have to validate their input in case of broken or malicious clients, but they just drop bogus values.) If the user enters a string that Python's built-in int() can't convert to an integer, IntWidget's parse() method raises FormValueError (also defined in the quixote.form.widget module). This exception is handled by Quixote's form framework, but if you're using widget objects on their own, you'll have to handle it yourself.

IntWidget.parse() always returns an integer or None.

IntWidget(name : string,
          value : int = None,
          size : int = None,
          maxlength : int = None)

FloatWidget

FloatWidget is identical to IntWidget, except:

• value must be a float
• parse() returns a float or None
• parse() raises FormValueError if the string entered by the user cannot be converted by Python's built-in float() function

OptionSelectWidget

OptionSelectWidget is simply a SingleSelectWidget that uses a bit of Javascript to automatically submit the current form as soon as the user selects a value. This is useful for very simple one-element forms where you don't want to bother with a submit button, or for very complex forms where you need to revamp the user interface based on a user's selection. Your form-processing code could then detect that style of form submission, and regenerate a slightly different form for the user. (Or you could treat it as a full-blown form submission, if the only widget of interest is the OptionSelectWidget.)

For example, if you're asking a user for their address, some of the details will vary depending on which country they're in. You might make the country widget an OptionSelectWidget: if the user selects "Canada", you'll ask them for a province and a postal code; if they select "United States", you ask for a state and a zip code; and so forth. (I don't really recommend a user interface that works this way: you'll spend way too much time getting the details right ["How many states does Australia have again?"], and you're bound to get something wrong -- there are over 200 countries in the world, after all.)

Be warned that since OptionSelectWidget relies on Javascript to work, using it makes immediately makes your application less portable and more fragile. One thing to avoid: form elements with a name of submit, since that masks the Javascript function called by OptionSelectWidget.