MvInterface: wm wait for connection?

[slactjohnson]

Current Behavior

The wm method tries to immediately return, without waiting for the PV to connect.

Expected Behavior

This is in contrast with the user_readback signal, which implements a timeout.

Context / environment

This lead to a SmarAct motor class erroring out when attempting to use it as part of a script.

Steps to Reproduce (for bugs)

Script:

from pcdsdevices.epics_motor import SmarAct
motor = SmarAct('LM1K2:MCS2:01:m10', name='tst diag motor')
print(motor.wm())

[ZLLentz]

Pros:

• user scripts and interactive use less likely to error in confusing ways

Cons:

• scripts that run with never-connecting devices get slowed down
• some movable devices may not require full connection to return their position

Maybe implement similar to:

def wm():
    try:
        return self.position
    except DisconnectedError:
        self.wait_for_connection()
        return self.position