dev: specification of the interface of the Sweep class

[asarhaddon]

Hello.

Some changes I have submitted for the Sweep class have been reverted (without much comments), I have also reverted the related changes in tests (6eb24f2, d09b55e, dbea311). And now python (rightfully) complains because the default value Properties() for the property field of the dataclass Sweep is mutable.
This dance (and lots of anterior commits) could probably be avoided by first explicitly defining the intent of this string, either in comments or doc strings.
Here are a few questions that a newcomer like me would like to see answered in the code.

• Why a separate Properties class? How are its fields different from the other ones in the Sweep class?

• Is it possible to use private fields in the usual way? Namely:

def set_start(self, start): with self._lock: self._start = start
def start(self): return self._start
def span(self): return self._end - self._start

Such declarations make evident that other classes should not modify self.start or self.span (which are functions) and self._start (which is private).

• I suggest to remove the @property syntactic sugar, which trades some confusion for a few keystrokes. The code does not contain much comments, it may be useful to search all calls to sweep.set_start. Also, the fact that implementations in the Sweep class do use hidden accessors is surprising, they are intended for public interfaces.

• What is the intent of self.lock? In some places, it seems that it should be a private field of the Sweep class, used in setters like above, in order to ensure that any change of the field value is protected. But...

  DeviceSettings.py sets sweep.points without locking.

  SweepSettings.py locks while calling self.app.vna.setTXPower(...), which does not seem to affect self.app.sweep.

• Comparison of Sweep classes should probably use a documented function instead of redefining the python equality, so that it is easy to find where it is called from. For example, this portion of SweepWorker.py

with self.app.sweep.lock:
    sweep = self.app.sweep.copy()
if sweep != self.sweep:  # parameters changed
    self.sweep = sweep

is hard to understand even with a comment.
May it be simplified like this ? (the answer probably depends on the intent of the lock)

if self.app.sweep != self.sweep:  # parameters changed
    self.sweep = self.app.sweep.copy()

Thanks