Safer Sympify

Convert unsanitized user input into SymPy expression.

This does not prevent all possible attacks. However, this is much safer than using eval(), which SymPy still does.

See SymPy PR12524 for more details: https://github.com/sympy/sympy/pull/12524

Examples

    Create a SymPy expression from user input. 
    This uses pure Python syntax. 
    Whitelisted operators and functions only are allowed.
    >>> expr = SaferSympify().str2sympy('-sqrt(1 + a**b*b)/((a**b)*b+1)')
    >>> expr
    -1/sqrt(a**b*b + 1)

    Get free symbols:
    >>> sorted(expr.free_symbols, key=lambda x: str(x))
    [a, b]

    Evaluate expression:
    >>> expr.evalf(subs={'a': 1, 'b': 3, 'c': 5})  # Note extra values can be passed too
    -0.500000000000000

    Simplify expression:
    >>> expr.simplify()
    -1/sqrt(a**b*b + 1)

    Pretty-print expression as Latex (could be displayed in browser with MathJax)
    >>> sympy.latex(expr)
    '- \\frac{1}{\\sqrt{a^{b} b + 1}}'