Disallow inserting attributes into an instance of Session

[marcoskirsch]

Say you have this code:

def test_take_simple_measurement_works(device_info):
    with nidmm.Session(device_info['name']) as session:
        session.rannge = 50 # Coerces up!
        value = session.read(1000) != 0 # Assumes DMM reading is not exactly zero to support non-

Interestingly, this appears to work, but notice the typo when setting the range property! The range property was never set on the session and no error occurred.

Given that:

• Our Python bindings are abstractions on top of pre-established APIs
• We'll release as 0.1 and there's a chance that attribute names will get tweaked (as happened in test_system_nidmm.py test_ViSession_attribute fails #95)

I propose that we disallow inserting any attributes into an instance of Session. How to do that is TBD.

[marcoskirsch]

Defining __setattr__ is most likely the way to go.