human
Here's a good function header given the following:
I wrote the below code

    expr = sympify(expr)
    try:
        return expr._eval_simplify(ratio=ratio, measure=measure)
    except AttributeError:
        pass
    original_expr = expr = signsimp(expr)
    from sympy.simplify.hyperexpand import hyperexpand
    from sympy.functions.special.bessel import BesselBase
    from sympy import Sum, Product
    if ((not isinstance(expr, Basic)) or (not expr.args)):
        return expr
    if (not isinstance(expr, (Add, Mul, Pow, ExpBase))):
        if (isinstance(expr, Function) and hasattr(expr, 'inverse')):
            if ((len(expr.args) == 1) and (len(expr.args[0].args) == 1) and isinstance(expr.args[0], expr.inverse(argindex=1))):
                return simplify(expr.args[0].args[0], ratio=ratio, measure=measure, fu=fu)
        return expr.func(*[simplify(x, ratio=ratio, measure=measure, fu=fu) for x in expr.args])
    def shorter(*choices):
        'Return    the    choice    that    has    the    fewest    ops.    In    case    of    a    tie,\n                                the    expression    listed    first    is    selected.'
        if (not has_variety(choices)):
            return choices[0]
        return min(choices, key=measure)
    expr = bottom_up(expr, (lambda w: w.normal()))
    expr = Mul(*powsimp(expr).as_content_primitive())
    _e = cancel(expr)
    expr1 = shorter(_e, _mexpand(_e).cancel())
    expr2 = shorter(together(expr, deep=True), together(expr1, deep=True))
    if (ratio is S.Infinity):
        expr = expr2
    else:
        expr = shorter(expr2, expr1, expr)
    if (not isinstance(expr, Basic)):
        return expr
    expr = factor_terms(expr, sign=False)
    expr = hyperexpand(expr)
    expr = piecewise_fold(expr)
    if expr.has(BesselBase):
        expr = besselsimp(expr)
    if ((expr.has(TrigonometricFunction) and (not fu)) or expr.has(HyperbolicFunction)):
        expr = trigsimp(expr, deep=True)
    if expr.has(log):
        expr = shorter(expand_log(expr, deep=True), logcombine(expr))
    if expr.has(CombinatorialFunction, gamma):
        expr =...

What's a good function header?
assistant
#Here's a good function header.

def simplify(expr, ratio=1.7, measure=count_ops, fu=False):