<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def length_curve(obj):
 """ Computes the approximate length of the parametric curve. Uses the following equation to compute the approximate length: .. math:: \\sum_{i=0}^{n-1} \\sqrt{P_{i + 1}^2-P_{i}^2} where :math:`n` is number of evaluated curve points and :math:`P` is the n-dimensional point. :param obj: input curve :type obj: abstract.Curve :return: length :rtype: float """

    if not isinstance(obj, abstract.Curve):
        raise GeomdlException("Input shape must be an instance of abstract.Curve class")

    length = 0.0
    evalpts = obj.evalpts
    num_evalpts = len(obj.evalpts)
    for idx in range(num_evalpts - 1):
        length += linalg.point_distance(evalpts[idx], evalpts[idx + 1])
    return length