Regular expressions¶

When a constraint type of Regex is specified, the corresponding constraint value is normalized as follows:

csv2shex will try to replace the value with a compiled Python regular expression for value.
If the value does not compile correctly (e.g., because it is malformed), csv2shex will replace the constraint value with None so as not to pass a bad regular expression to processes or applications downstream.
If no constraint constraint value is specified, csv2shex will leave it unspecified.

propertyID	constraint_value	constraint_type
:status	approved_*	Regex
:status		Regex
:status	approved_(*	Regex
:status	/approved_*/	Regex
:status	^2020 August	Regex

This is interpreted as:

DCAP
    Shape
        shapeID: @default
        start: True
        Statement
            propertyID: :status
            value_type: Literal
            constraint_value: re.compile('approved_*')
            constraint_type: Regex
        Statement
            propertyID: :status
            value_type: Literal
            constraint_type: Regex
        Statement
            propertyID: :status
            value_type: Literal
            constraint_type: Regex
        Statement
            propertyID: :status
            value_type: Literal
            constraint_value: re.compile('/approved_*/')
            constraint_type: Regex
        Statement
            propertyID: :status
            value_type: Literal
            constraint_value: re.compile('^2020 August')
            constraint_type: Regex

Note:

For the third statement, csv2shex drops the malformed constraint value and displays an error message:
```
'approved_(*' is not a valid (Python) regular expression.
```
While regular expressions are commonly enclosed in forward slashes, csv2shex reads the forward slashes as part of the regular expression. In other words, re.compile(‘/NOW/’) will match the string /NOW/. Enclosing quotes will also be considered part of the regular expression, so a constraint value of ‘NOW’ will be normalized as re.compile(“‘NOW’”).
Regular expressions can include spaces.
The Regex constraint typically applies to a Literal constraint value, so where a value type has been left unspecified, csv2shex will assign to it the value ‘Literal’. However, where a different value type has already been assigned (eg, URI or BNode), csv2shex will leave the assigned value unchanged; the user is responsible for catching such errors.