human
Complete the below
def _smart_subs(expr, sub_dict):

    ''''Performs subs, checking for conditions that may result in `nan` or
    `oo`, and attempts to simplify them out.
    The expression tree is traversed twice, and the following steps are
    performed on each expression node:
    - First traverse:
    Replace all `tan` with `sin/cos`.
    - Second traverse:
    If node is a fraction, check if the denominator evaluates to 0.
    If so, attempt to simplify it out. Then if node is in sub_dict,
    sub in the corresponding value.'
    '''
 What is a the Python program you requested?
assistant
#Here is the Python program you requested.
    expr = _crawl(expr, _tan_repl_func)
    def _recurser(expr, sub_dict):
        (num, den) = _fraction_decomp(expr)
        if (den != 1):
            denom_subbed = _recurser(den, sub_dict)
            if (denom_subbed.evalf() == 0):
                expr = simplify(expr)
            else:
                num_subbed = _recurser(num, sub_dict)
                return (num_subbed / denom_subbed)
        val = _sub_func(expr, sub_dict)
        if (val is not None):
            return val
        new_args = (_recurser(arg, sub_dict) for arg in expr.args)
        return expr.func(*new_args)
    return _recurser(expr, sub_dict)