memory location in unicode strings

Question

I know someone explain why when I create equal unicode strings in Python 2.7 they do not point to the same location in memory As in "normal" strings

>>> a1 = 'a'
>>> a2 = 'a'
>>> a1 is a2
True

ok that was what I expected, but

>>> ua1 = u'a'
>>> ua2 = u'a'
>>> ua1 is ua2
False

why? how?

Answer 1

I think regular strings are interned but unicode strings are not. This simple test seems to support my theory (Python 2.6.6):

>>> intern("string")
'string'
>>> intern(u"unicode string")

Traceback (most recent call last):
  File "<pyshell#18>", line 1, in <module>
    intern(u"unicode string")
TypeError: intern() argument 1 must be string, not unicode