assignment operator about list in Python

Question

I am a beginner in Python, I cannot understand assignment operator clearly, for example:

list1 = [\"Tom\", \"Sam\", \"Jim\"]
list2 = list1

Answer 1

In your example the identifiers list1 and list2 are references to the same underlying object (just different names for the same thing).

id() can be used to see if the same underlying object is being referenced.

>>> list1 = ["Tom", "Sam", "Jim"]
>>> list2 = list1
>>> id(list1)
44259368
>>> id(list2)
44259368

To create a copy of the defined list use the [:] notation, or deepcopy as Matthew has mentioned. You'll notice that when this is done the location/id has changed.

>>> list3 = list1[:]
>>> id(list3)
44280208

About the id command:

>>> help(id)
Help on built-in function id in module __builtin__:

id(...)
    id(object) -> integer

    Return the identity of an object.  This is guaranteed to be unique among
    simultaneously existing objects.  (Hint: it's the object's memory address.)