Definition Nodes

Using the checker classes themselves, defining complex checkers can lead to complicated code that is harder to parse, as in this simple rolodex entry:

nick = BoolCheck('nick', required=False)
fname = TextCheck('first', min_length = 1)
fname.addattribute(nick)

lname = TextCheck('last', min_length = 1)
code = IntCheck('code', min_occurs = 1, max_occurs = 5)
code.addattribute(TextCheck('word', required=False) )
name = XCheck('name', children=[fname, lname, code])

emailtype = SelectionCheck('type', values = ['home','work', 'personal'])
email = EmailCheck('email', max_occurs=2)
email.addattribute(emailtype)
street = TextCheck('street')
city = TextCheck('city')

address = XCheck('address', children=[street, city, email], max_occurs=4)

dude = XCheck('dude', children=[name, address],
    help="A simple contact list item")
idch = IntCheck('id', required=True)
dude.addattribute(idch)

This style creates the children checkers, then creates the main object. Alternately, this could be created in a top-down manner:

dude = XCheck('dude', help="A simple contact list item")

# can add some attributes without creating them seprately first
dude.addattribute(IntCheck('id', required=True))

# complex children can be defined and added

name = XCheck('name')
fname = TextCheck('first', min_length = 1)
fname.addattribute(BoolCheck('nick', required=False))
lname = TextCheck('last', min_length = 1)
code = IntCheck('code', min_occurs = 1, max_occurs = 5)
code.addattribute(TextCheck('word', required=False) )

name.add_children(fname, lname, code)

# ... etc

The load_checker() function allows users to write definition nodes in XML:

dude_defition = """<xcheck name="dude">
<attributes>
    <int name="id" required="true" />
</attributes>
<children>
    <xcheck name="name">
        <text name="first" min_length="1">
            <attributes>
                <text name="nick" required="false"/>
            </attributes>
        </text>
        <text name="last" min_length="1" />
        <int name="code" min_occurs="1" max_accurs="5">
            <attributes>
                <text name="word" required="false" />
            </attributes>
        </int>
    </xcheck>
    <xcheck name="address" max_occurs="4">
        <children>
            <text name="street" />
            <text name="city" />
            <email name="email" max_occurs="2">
                <attributes>
                    <selection name="type" values="home, work, personal" />
                </attrubutes>
            </email>
        </children>
    </xcheck>
</children>
</xcheck>
"""

Note

Future plans include removing the children tag, assuming every child under the xchecx definition node is a child unless they are under the attributes child or has a special is_attribute xml attribute.

Other future plans include an RNG to XCheck converter.

Definition nodes use tags defining the checker:

tag	Checker Created
xcheck	XCheck
text	TextCheck
email	EmailCheck
url	URLCheck
int	IntCheck
decimal	DecimalCheck
datetime	DatetimeCheck
bool	BoolCheck
selection	SelectionCheck
list	ListCheck

Each XML element must have a name attribute, which is the tag the checker will look for. Other attributes are mapped to the keyword arguments that are called when load_checker() creates the XCheck object.

If you define your own checker class (see Rolling your own), you can get load_checker() to accept your class by calling:

xcheck.loader.LOAD_RULES[name] = YourClass

before you call load_checker().

The load_checker() function recognizes several custom attributes. If your custome checker class uses these attributes, load_cheker() will work.

attribute	Treated as
min	int or decimal
max	int or decimal
min_value	int or decimal
max_value	int or decimal
min_length	int
max_length	int
min_occurs	int
max_occurs	int
required	bool
unique	bool
check_children	bool
ordered	bool
allow_none	bool
allow_blank	bool
none_is_false	bool
pattern	string
delimiter	string [1]
error	exception [2]

If you have a custom attribute not listed here, load_checker() will fail.

Footnotes

[1]	The SelectionCheck class does not have a delimiter, but the definition node does.

[2]	If the exception class is not in globals() then load_checker() will raise an UnmatchedError