Colin J. Williams
1/15/2008 4:25:00 PM
Colin J. Williams wrote:
> Neil Cerutti wrote:
>> On Jan 15, 2008 10:10 AM, <skip@pobox.com> wrote:
>>> I've noticed that I can update() a set with a list but I can't extend a set
>>> with a list using the |= assignment operator.
>>>
>>> >>> s = set()
>>> >>> s.update([1,2,3])
>>> >>> s
>>> set([1, 2, 3])
>>> >>> s |= [4,5,6]
>>> Traceback (most recent call last):
>>> File "<stdin>", line 1, in <module>
>>> TypeError: unsupported operand type(s) for |=: 'set' and 'list'
>>> >>> s |= set([4,5,6])
>>> >>> s
>>> set([1, 2, 3, 4, 5, 6])
>>>
>>> Why is that? Doesn't the |= operator essentially map to an update() call?
>> No, according to 3.7 Set Types, s | t maps to s.union(t).
>>
> If the RHS is a set then it works OK:
>
> *** Python 2.5.1 (r251:54863, Apr 18
> 2007, 08:51:08) [MSC v.1310 32 bit
> (Intel)] on win32. ***
>>>> import sets
>>>> s1= sets.Set([2, 4, 5])
> Set([2, 4, 5])
>>>> s1= sets.Set([2, 4, 5])
>>>> s2= sets.Set([4, 5, 6])
>>>> s1|s2
> Set([2, 4, 5, 6])
>>>> s1|=s2
>>>> s1
> Set([2, 4, 5, 6])
>
> It could be modified to handle any
> iterable on the RHS.
>
> Colin W.
>
I'm sorry, there appears to be a bug:
# tSet.py
import sets
s1= sets.Set([1, 2, 3])
s1.union_update([3, 4,5])
print(s1)
s2= sets.Set([6, 7, 8])
s1 |+ s2 # This fails:
exceptions.TypeError: bad operand type
for unary +: 'Set'
print s1
Colin W.