sympy_utils

prairielearn.sympy_utils

Utility functions for parsing and evaluating SymPy expressions.

convert_string_to_sympy

convert_string_to_sympy(
    expr: str,
    variables: Iterable[str] | None = None,
    *,
    allow_hidden: bool = False,
    allow_complex: bool = False,
    allow_trig_functions: bool = True,
    custom_functions: Iterable[str] | None = None,
    assumptions: AssumptionsDictT | None = None,
) -> Expr

Convert a string to a sympy expression, with optional restrictions on the variables and functions that can be used. If the string is invalid, raise an exception with a message that can be displayed to the user.

Parameters:

Name	Type	Description	Default
expr	str	The string to convert to a sympy expression.	required
variables	Iterable[str] | None	A list of variable names that are allowed in the expression.	None
allow_hidden	bool	Whether to allow hidden variables (like pi and e).	False
allow_complex	bool	Whether to allow complex numbers (like i).	False
allow_trig_functions	bool	Whether to allow trigonometric functions.	True
custom_functions	Iterable[str] | None	A list of custom function names that are allowed in the expression.	None
assumptions	AssumptionsDictT | None	A dictionary of assumptions for variables in the expression.	None

Examples:

>>> convert_string_to_sympy("n * sin(7*m) + m**2 * cos(6*n)", variables=["m", "n"])
n * sympy.sin(m * 7) + m * m * sympy.cos(n * 6)
>>> convert_string_to_sympy("-infty")
-sympy.oo
>>> convert_string_to_sympy("z**2 + y - x", variables=["x", "y", "z"], allow_complex=True, assumptions={"x": {"positive": False}, "z": {"complex": True}})

AssumptionsDictT module-attribute

AssumptionsDictT = dict[str, dict[str, Any]]

A dictionary of assumptions for variables in the expression.

Examples:

>>> {"x": {"positive": True}, "y": {"real": True}}