tag-expressions

tag-expressions

Package to evaluate logical tag expressions by using a modified version of the Shunting Yard algorithm <https://en.wikipedia.org/wiki/Shunting-yard_algorithm>_. This package is a Python port of cucumbers tag expression.

It's also used by radish <https://github.com/radish-bdd/radish>_.

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Installing

.. code:: bash

$ pip install tag-expressions

Here is a tease

.. code:: python

>>> 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

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