HElement
May 30, 2006

HElement, or HTML-element, is a simple, straight-forward, and non-magical HTML generation engine. An HElement is made of two parts: attrs - the attributes of the tag, and elems - the sub-elements of the tag. Sub-elements can be either HElements by themselves, or plain objects whose str() is used to embed them into the enclosing element.

No validations are performed on the structure -- it's up to you to create something the browser can chew. If you want to do Table(Html(TextField(name = "blah"))), be my guest. Both pretty (indentation and newlines) and compact HTML can be generated.

Code

#
# module helement.py
# requires the AttrDict recipe
#
from AttrDict import AttrDict


class HElementError(Exception):
    pass

_html_mapping = (
    ("&", "&"),
    ("  ", "  "),
    (">", ">"),
    ("<", "&lt;"),
    ('"', "&quot;"),
)

def encode_html(obj):
    text = str(obj)
    for chr, enc in _html_mapping:
        text = text.replace(chr, enc)
    return text

class HElement(object):
    _name = None
    _enclosing = True
    _defaults = {}
    _pretty = True
    
    def __init__(self, *elems, **attrs):
        if self._name is None:
            self.name = self.__class__.__name__.lower()
        else:
            self.name = self._name
        if self._enclosing:
            self.elems = list(elems)
        elif elems:
            raise ElementError("element is not a container")
        self.attrs = AttrDict(self._defaults)
        AttrDict.update(self.attrs, attrs)
    
    def _render(self, nesting, pretty):
        items = []
        if pretty:
            indent = "    " * nesting
            subindent = "    " * (nesting + 1)
            items.append(indent)
        items.append("<")
        items.append(self.name)
        for k, v in self.attrs:
            if isinstance(v, bool):
                if v:
                    items.append(" ")
                    items.append(k)
            else:
                items.append(" ")
                items.append(k)
                items.append('="')
                items.append(encode_html(v))
                items.append('"')
        items.append(">")
        if pretty: 
            items.append("\n")
        if self._enclosing:
            for elem in self.elems:
                if isinstance(elem, HElement):
                    items.extend(elem._render(nesting + 1, pretty))
                elif pretty:
                    for line in encode_html(elem).splitlines():
                        items.append(subindent)
                        items.append(line)
                        items.append("\n")
                else:
                    items.append(" ".join(encode_html(elem).splitlines()))
            if pretty:
                items.append(indent)
            items.append("</")
            items.append(self.name)
            items.append(">")
            if pretty:
                items.append("\n")
        return items
    
    def render(self, nesting = 0, pretty = None):
        if pretty is None:
            pretty = self._pretty
        return "".join(self._render(nesting, pretty))
    
    def __repr__(self):
        return self.render(pretty = False)
    
    __str__ = render


class SimpleElement(HElement): 
    _enclosing = False

# headers
class Root(HElement): _name = "html"
class Head(HElement): pass
class Title(HElement): pass
class Meta(HElement): pass
class Body(HElement): pass

# formatting
class Break(SimpleElement): _name = "br"
class Para(HElement): _name = "p"
class Bold(HElement): _name = "b"
class Italics(HElement): _name = "i"
class Underline(HElement): _name = "u"
class Font(HElement): pass
class BulletGroup(HElement): _name = "ul"
class Bullet(HElement): _name = "li"
class Quote(HElement): _name = "q"
class Pre(HElement): pass
class Mono(HElement): _name = "tt"

# forms
class Form(HElement): pass
class Field(SimpleElement): _name = "input"
class TextField(Field): _defaults = {"type" : "text"}
class PasswordField(Field): _defaults = {"type" : "password"}
class CheckboxField(Field): _defaults = {"type" : "checkbox"}
class RadioButton(Field): _defaults = {"type" : "radio"}
class SubmitButton(Field): _defaults = {"type" : "submit"}
class ResetButton(Field): _defaults = {"type" : "reset"}
class SelectField(HElement): _name = "select"
class OptionField(HElement): _name = "option"
class TextArea(HElement): pass

# tables
class Table(HElement): pass
class Row(HElement): _name = "tr"
class Col(HElement): _name = "td"

Exampel

>>> f = Form(
...     "some text",
...     Table(
...         Row(
...             Col(
...                 "hello moshe",
...                 Bold("kaki\npipi"),
...                 TextField(name = "moshe"),
...                 Break(),
...                 "lala",
...                 bgcolor = "white"),
...         ),
...         Row(
...             Col(
...                 SubmitButton(value = "send")
...             )
...         ),
...         width = "100%",
...     ),
...     action = "login",
...     method = "post"
... )
>>>
>>> f
<form action="login" method="post">some text<table width="100%"><tr><td bgcolo
r="white">hello moshe<b>kaki pipi</b><input type="text" name="moshe"><br>lala<
/td></tr><tr><td><input type="submit" value="send"></td></tr></table></form>

>>> print f
<form action="login" method="post">
    some text
    <table width="100%">
        <tr>
            <td bgcolor="white">
                hello moshe
                <b>
                    kaki
                    pipi
                </b>
                <input type="text" name="moshe">
                <br>
                lala
            </td>
        </tr>
        <tr>
            <td>
                <input type="submit" value="send">
            </td>
        </tr>
    </table>
</form>

>>> f.elems[1].elems.append("and some more text")
>>> f.attrs.method = "get"
>>>
>>> print f
<form action="login" method="get">
    some text
    <table width="100%">
        <tr>
            <td bgcolor="white">
                hello moshe
                <b>
                    kaki
                    pipi
                </b>
                <input type="text" name="moshe">
                <br>
                lala
            </td>
        </tr>
        <tr>
            <td>
                <input type="submit" value="send">
            </td>
        </tr>
        and some more text
    </table>
</form>