Tag Expressions

2.0.1 · active · verified Thu Apr 16

Tag Expressions is a Python library that provides an implementation for parsing and evaluating Cucumber Tag Expressions. It allows you to check if a set of tags matches a given boolean expression string. The current version is 2.0.1, with releases typically occurring for maintenance or minor feature additions, following a stable core API.

Common errors

```
TypeError: evaluate() missing 1 required positional argument: 'tags'
```
cause The `evaluate` function was called without the required `tags` argument.

fix Provide a list or other iterable of tag strings as the second argument to `evaluate`. Example: `evaluate('my_expression', ['tag1', 'tag2'])`.
```
TypeError: argument of type 'str' is not iterable
```
cause A single string was passed as the `tags` argument to `evaluate` instead of an iterable of strings.

fix Wrap your single tag string in a list. Example: `evaluate('my_expression', ['my_tag'])` instead of `evaluate('my_expression', 'my_tag')`.
```
NameError: name 'evaluate' is not defined
```
cause The `evaluate` function was used without being correctly imported.

fix Add `from tag_expressions import evaluate` at the top of your Python file.

Warnings

breaking Version 2.0.0 dropped support for Python 2.x. The library is now Python 3.8+ only.
Fix: Ensure your project is running on Python 3.8 or newer. If you need Python 2 compatibility, you must use a version prior to 2.0.0 (e.g., `pip install 'tag-expressions<2.0.0'`).
gotcha The `evaluate` function expects the `tags` argument to be an iterable (e.g., a list or set) of strings, not a single string.
Fix: Always pass a list or other iterable of tag strings, even if there's only one tag. For example, `evaluate('tag1', ['tag1'])` not `evaluate('tag1', 'tag1')`.
gotcha This library implements the *Cucumber* Tag Expressions grammar, which has specific syntax and operator precedence. It is not a general-purpose boolean expression parser.
Fix: Refer to the Cucumber Tag Expressions documentation for the supported grammar and behavior to avoid unexpected evaluation results. Only `and`, `or`, `not`, and parentheses are supported.

Install

pip install tag-expressions Install latest version

Imports

evaluate
```
from tag_expressions import evaluate
```

Quickstart

This quickstart demonstrates how to import and use the `evaluate` function with various boolean tag expressions and tag lists.

from tag_expressions import evaluate

# Basic tag evaluation
assert evaluate('tag1', ['tag1']) is True
assert evaluate('tag1', ['tag2']) is False

# AND operator
assert evaluate('tag1 and tag2', ['tag1', 'tag2']) is True
assert evaluate('tag1 and tag2', ['tag1']) is False

# OR operator
assert evaluate('tag1 or tag2', ['tag1']) is True
assert evaluate('tag1 or tag2', ['tag2']) is True

# NOT operator
assert evaluate('not tag1', ['tag2']) is True
assert evaluate('not tag1', ['tag1']) is False

# Combined expression
assert evaluate('(tag1 or tag2) and not tag3', ['tag1', 'tag4']) is True
assert evaluate('(tag1 or tag2) and not tag3', ['tag2', 'tag4']) is True
assert evaluate('(tag1 or tag2) and not tag3', ['tag1', 'tag3']) is False

print("All tag expressions evaluated successfully!")

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