newbie Q: sequence membership

saccade trivik at gmail.com
Sat Nov 17 08:02:12 CET 2007


>>> a, b = [], []
>>> a.append(b)
>>> b.append(a)
>>> b in a
True
>>> a in a
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: maximum recursion depth exceeded in cmp
>>>
>>> a is a[0]
False
>>> a == a[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: maximum recursion depth exceeded in cmp

----------

I'm a little new to this language so my mental model on whats going on
may need to be refined.

I expect "a in a" to evaluate to "False". Since it does not it may be
that while checking equality it uses "==" and not "is". If that is the
reason then  the question becomes why doesn't "a == a[0]" evaluate to
"False"? As a side, and if that is the reason, is there a version of
"in" that uses "is"? "a is in a" does not work.

Thankx,
Trivik



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