You should use these comparisons for their semantics.
Use is to check identity and == to check equality.

In Python names refer to objects, for example in this case value1 and value2 refer to an int instance storing the value 1000:

value1 = 1000
value2 = value1
>>> value1 == value2
True
>>> value1 is value2
True

In the following example the names value1 and value2 refer to different int instances, even if both store the same integer. Because the same value (integer) is stored == will be True, that's why it's often called "value comparison". However is will return False because these are different objects:

>>> value1 = 1000
>>> value2 = 1000

>>> value1 == value2
True
>>> value1 is value2
False