tag-expressions

Package to evaluate logical tag expressions by using a modified version of the Shunting Yard algorithm. This package is a Python port of cucumbers tag expression.

It's also used by radish.

Installing

$ pip install tag-expressions

Here is a tease

>>> from tagexpressions import parse
>>>
>>> expression = '( a and b ) or ( c and d )'
>>> compiled_expression = parse(expression)
>>> print(compiled_expression)
( ( a and b ) or ( c and d ) )
>>>
>>> data = ['a', 'b', 'c', 'd']
>>> assert compiled_expression.evaluate(data) == True
>>>
>>> data = ['a', 'c']
>>> assert compiled_expression.evaluate(data) == False
>>>
>>>
>>> expression = 'not a or b and not c or not d or e and f'
>>> compiled_expression = parse(expression)
>>> print(compiled_expression)
( ( ( not ( a ) or ( b and not ( c ) ) ) or not ( d ) ) or ( e and f ) )
>>>
>>> data = ['b', 'e', 'f']
>>> assert compiled_expression.evaluate(data) == True
>>>
>>> data = ['a', 'c', 'd']
>>> assert compiled_expression.evaluate(data) == False

Usage

Available operators

• or - "or" conjunction of two given variables
• and - "and" conjunction of two given variables
• not - negation of a single variable

Every other token given in an infix is considered a variable.

Operator precedence

From high to low:

• ()
• or
• and
• not