>>> a = "my string"
>>> b = "my string"
>>> id(a)
7570480
>>> id(b)
7574128
>>> id("my string")
7574192
>>> id("my string")
7574192
>>> del(a)
>>> del(b)
>>> id("my string")
7574320

>>> a = "my string"
>>> b = "my string"
>>> a is b
False
>>> def f():
...     a = "my string"
...     b = "my string"
...     return a is b
...
>>> f()
True

>>> a = "my string"; b = "my string"
>>> id(a)
11175280
>>> id(b)
11175280