ForLoopPT duration evaluation fails with floor arguments

[shumpohl]

from qupulse.pulses import *
body = FunctionPT('sin(2*pi*i*t*f)', '1/f')
pt = ForLoopPT(body , 'i', 'floor(total_time*f)')
pt.duration.evaluate_in_scope({'f': 1., 'total_time': 500})

fails with

  File "<lambdifygenerated-1>", line 2, in _lambdifygenerated
    return select([less_equal(floor(f*total_time), 0),True], [0,(builtins.sum(f**(-1.0) for i in range(0, amax((1,floor(f*total_time)), axis=0) - 1+1)))], default=nan)

TypeError: 'numpy.float64' object cannot be interpreted as an integer