CmdDef arguments fail if not provided as keyword arguments

[taalexander]

Information

• Qiskit Terra version:
• Python version:
• Operating system:

What is the current behavior?

cmd_def.get('u3', control, np.pi, 0, np.pi)

Raises error

---------------------------------------------------------------------------
PulseError                                Traceback (most recent call last)
<ipython-input-16-5eef41f492e0> in <module>
----> 1 control_xgate = cmd_def.get('u3', control, np.pi, 0, np.pi)

~/anaconda3/envs/qiskit/lib/python3.7/site-packages/qiskit/pulse/cmd_def.py in get(self, cmd_name, qubits, *params, **kwparams)
    134 
    135             if isinstance(schedule, ParameterizedSchedule):
--> 136                 return schedule.bind_parameters(*params, **kwparams)
    137 
    138             return schedule.flatten()

~/anaconda3/envs/qiskit/lib/python3.7/site-packages/qiskit/pulse/schedule.py in bind_parameters(self, *args, **kwargs)
    414                 predefined = self.parameters
    415             sub_params = {k: v for k, v in named_parameters.items() if k in predefined}
--> 416             schedules.append(param_sched(**sub_params))
    417 
    418         # construct evaluated schedules

~/anaconda3/envs/qiskit/lib/python3.7/site-packages/qiskit/pulse/schedule.py in __call__(self, *args, **kwargs)
    424     def __call__(self, *args: List[Union[float, complex]],
    425                  **kwargs: Dict[str, Union[float, complex]]) -> Schedule:
--> 426         return self.bind_parameters(*args, **kwargs)

~/anaconda3/envs/qiskit/lib/python3.7/site-packages/qiskit/pulse/schedule.py in bind_parameters(self, *args, **kwargs)
    414                 predefined = self.parameters
    415             sub_params = {k: v for k, v in named_parameters.items() if k in predefined}
--> 416             schedules.append(param_sched(**sub_params))
    417 
    418         # construct evaluated schedules

~/anaconda3/envs/qiskit/lib/python3.7/site-packages/qiskit/qobj/converters/pulse_instruction.py in gen_fc_sched(*args, **kwargs)
    346 
    347             def gen_fc_sched(*args, **kwargs):
--> 348                 phase = abs(phase_expr(*args, **kwargs))
    349                 return commands.FrameChange(phase)(channel) << t0
    350 

~/anaconda3/envs/qiskit/lib/python3.7/site-packages/qiskit/pulse/parser.py in __call__(self, *args, **kwargs)
    134                 return PulseExpression(expr, self._partial_binding)
    135             else:
--> 136                 raise PulseError('Parameters %s are not all bound.' % self.params)
    137         return expr.body.n
    138 

PulseError: "Parameters ['P2'] are not all bound."

Steps to reproduce the problem

What is the expected behavior?

Suggested solutions

I believe this may have something to do with qiskit assuming a specific format for the order/names of commands, these should instead be ordered alphabetically. As they will typically be P{n}.