Exception in SymPy Live while running example from docstring of KanesMethod object

[Keshavinee]

I executed the example mentioned in the docstring of the KanesMethod object. It shows me an error in the Sympy Live shell when I tried to display the variable "FL" (Forces/torque list).

from sympy import symbols
from sympy.physics.mechanics import dynamicsymbols, ReferenceFrame
from sympy.physics.mechanics import Point, Particle, KanesMethod
q, u = dynamicsymbols('q u')
qd, ud = dynamicsymbols('q u', 1)
m, c, k = symbols('m c k')
N = ReferenceFrame('N')
P = Point('P')
P.set_vel(N, u * N.x)
kd = [qd - u]
FL = [(P, (-k * q - c * u) * N.x)]
pa = Particle('pa', P, m)
BL = [pa]
FL
Exception in SymPy Live of type
<type 'exceptions.RuntimeError'>
for reference the last 5 stack trace entries are
Traceback (most recent call last):
File "/base/data/home/apps/ssympy-live-hrd/66.426491309333028408/app/handlers.py", line 271, in post
live.evaluate(statement, session, printer, stream)
File "/base/data/home/apps/ssympy-live-hrd/66.426491309333028408/app/shell.py", line 370, in evaluate
session.set_global('_', val)
File "/base/data/home/apps/ssympy-live-hrd/66.426491309333028408/app/models.py", line 61, in set_global
blob = self.fast_dumps(value, 1)
File "/base/data/home/apps/ssympy-live-hrd/66.426491309333028408/app/models.py", line 127, in fast_dumps
p.dump(obj)
File "/base/alloc/tmpfs/dynamic_runtimes/python27g/6138304582e07bba/python27/python27_dist/lib/python2.7/pickle.py", line 224, in dump
self.save(obj)
RuntimeError: maximum recursion depth exceeded while calling a Python object