evalis 0.2.1

A polyglot, safe, user-friendly expression evaluator.

Evalis

A secure, user-friendly expression evaluator for Python.

Early Release: This is an early release with core functionality. More features are in active development. Check the main project for roadmap and updates.

Installation

pip install evalis

Quick Start

from evalis import evaluate_expression

context = {"a": {"b": 5}}
value = evaluate_expression("a.b + 2", context)

print(value)  # 7

Features

• Safe evaluation - No eval(). No access to global namespace.
• Simple syntax - Familiar expressions with property access, operators, and comprehensions.
• Type-safe - Full type hints included for static type checking.

Supported Operations

• Arithmetic: +, -, *, /
• Comparison: ==, !=, <, <=, >, >=
• Logical: and, or, not
• Property access: obj.property, obj['key']
• Array access: arr[0]
• List comprehensions: [x * 2 for x in numbers]
• Membership: x in collection
• String literals: Both 'single' and "double" quotes supported

Note on + operator:

• Numbers: 5 + 3 → 8
• Strings: "hello" + "world" → "helloworld" (coerces primitives to string)
• Arrays: [1, 2] + [3, 4] → [1, 2, 3, 4]
• Mixed types (list + string) will raise EvalisError

API Reference

evaluate_expression(expression, context, options)

Evaluates an expression string with the given context.

Parameters:

• expression (str): The expression to evaluate
• context (dict): Variable context for the expression
• options (EvaluatorOptions, optional): Evaluation options

Returns: The evaluated result

Example:

from evalis import evaluate_expression

result = evaluate_expression("x * 2", {"x": 21})
# result = 42

parse_ast(expression)

Parses an expression into an AST without evaluating it.

Parameters:

• expression (str): The expression to parse

Returns: An AST node representing the expression

Example:

from evalis import parse_ast

ast = parse_ast("a + b")
# Returns: BinaryOpNode(op=BinaryOpType.ADD, left=..., right=...)

evaluate_ast(node, context, options)

Evaluates a pre-parsed AST node.

Parameters:

• node (EvalisNode): The AST node to evaluate
• context (dict): Variable context for evaluation
• options (EvaluatorOptions, optional): Evaluation options

Returns: The evaluated result

Example:

from evalis import parse_ast, evaluate_ast

ast = parse_ast("x + 1")
result = evaluate_ast(ast, {"x": 5})
# result = 6

EvaluatorOptions

Configuration options for evaluation.

Fields:

• should_null_on_bad_access (bool, default=False): Return None instead of raising errors on invalid property access

Example:

from evalis import evaluate_expression, EvaluatorOptions

options = EvaluatorOptions(should_null_on_bad_access=True)
result = evaluate_expression("foo.missing", {}, options)
# result = None (instead of raising an error)

More Information

This is the Python implementation of Evalis. For more details about the project:

• Main Project
• Architecture
• TypeScript Implementation

License

MIT