[BUG] Two Calendar objects with different events should not == each other

[Lx]

Describe the bug

Given two Calendar objects being loaded from a .ics file (one fresh, one cached):

calendar_a: icalendar.cal.Calendar
calendar_b: icalendar.cal.Calendar

I would expect (and attempted to rely upon) the == operator to reliably test whether they're the same or not (so I can avoid emitting "changes" when no changes have occurred).

calendar_a == calendar_b in all cases, regardless of whether their contents differ.

Expected behavior

The == operator correctly returns True or False depending on content.

[niccokunzmann]

Hello Alex, thanks for reporting this. Can you show a bit more code of how you load the calendars? When are they not equal? I did not fully understand how equality is determined. Also: How is this equality universal for all the sub-components?

[Lx]

Thanks for looking into this.

• In my use case, an ICS file is periodically downloaded and parsed via Calendar.from_ical(ics_file_as_bytes).
• On subsequent loads, the calendar needs to be compared with the previous one and act only if any event changes have occurred.
  • For avoidance of doubt, two different Calendar object instances are being compared—that is, id(calendar_a) != id(calendar_b).
• Most of the time, there is no change, and calendar_a == calendar_b has evaluated to True (as expected if Calendar equality checking has overridden the default mechanism of comparing ids).
• When the calendars do differ, calendar_a == calendar_b still evaluates to True (which is very unexpected).

I did not fully understand how equality is determined.

My expectation would be that calendar_a == calendar_b if and only if both calendars convey exactly the same information. If calendar_b had an additional event, or if one of its events' descriptions had been changed, I would expect that calendar_a != calendar_b. I may be misunderstanding your request for clarification—does this help?

How is this equality universal for all the sub-components?

Sorry, but I don't immediately understand what is being asked. Could you please rephrase?

Looking broadly at the codebase, it seems that the equality checking is done in CaselessDict:

icalendar/src/icalendar/caselessdict.py

Lines 88 to 89 in b8ff114

	def __eq__(self, other):
	return self is other or dict(self.items()) == dict(other.items())

which to me is doubly surprising, because at first glance, this should return False whenever two objects' items aren't in the exact same order, let alone if the two objects have a different number of keys. Could this be a hashing issue maybe?

[niccokunzmann]

I am wondering: Could you post two ICS files that evaluate as equal but are actually not equal?

[yassirasad]

@niccokunzmann
This issue occurred to me as well, you can verify it with any two ICS files which are different.

[niccokunzmann]

See also #570.