is and '==' i'm confused

[hshivaraj]

Hi all

>>> a = "this is test string"
>>> b = "this is test string"
>>> a == b
True

>>> a is b
False

>>> a = "test"
>>> b = "test"

>>> a is b
True

Why is a is b True in the second time compared to first time. If appears when the string with multiple words causes the it produce. AIs this because the underlying memory management is different?