Utility functions around state changes.

Latest release 20240214: Initial PyPI release.

Function delta(old, new, keys=None)

Return a mapping representing differences between the mappings old and new for the specified keys. If keys is not specified, the union of the keys of old and new is used.

The returned mapping has a key for each changed value. If the key does not exist in new the value is the MISSING sentinel object otherwise it is new[key]. Values are compared using ==; if that raises TypeError the values are considered not equal.

Example:

d1 = {1: 2, 3: 4, 5: 6} d2 = {1: 2, 3: 44, 7: 8} diff = delta(d1, d2) diff # doctest: +ELLIPSIS {3: 44, 5: <object object at ...>, 7: 8} diff[5] is MISSING True

Function monitor(get_state, keys=None, *, ifunchanged=False, interval=0.3, runstate=None)

A generator yielding 3-tuples of (old,new,delta(old,new,keys)) at poll intervals of interval seconds.

Parameters:

• get_state: a callable which polls the current state, returning a mapping
• keys: an optional iterable of keys of interest; if omitted, all the old and new mapping keys are examined
• ifunchanged: optional flag, default False; if true yield a tuple on every poll instead of only when a state change is seen
• interval: an optional interpoll time.sleep period, default 0.3s
• runstate: an optional RunState, whose cancelled attribute will be polled for loop termination

Release Log

Release 20240214: Initial PyPI release.