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Objects in Python may be mutable or immutable.

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Mutable objects may change value; immutable objects may not.

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Some immutable objects at times may look like they are changing their values.

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They are not actually changing their values though. The distinction is visible

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using the id function.

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Integers, container objects, strings, things like these may appear to be

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changing values when they are not.

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For example, here in the Python shell, we can create an object, and we'll call it x,

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and we'll assign a number to it, 42.

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Integers are immutable objects in Python, and if we look at the value, we see that it's 42.

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If we look at its type, we see that its type is int.

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If we look at the id, we see that it has this unique identifier.

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Now if I change the value of x, and remember it's an immutable object so I cannot

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change the value of an integer, but I assign x = 43,

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what I've actually done is I've changed this variable x to refer to a different integer.

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Variables in Python are references to objects.

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So this reference is now referring to a different object.

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If I type id of x, you'll see I get a different identifier.

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If I type x, I see that it's 43.

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If I assign x back to 42 and take its id, you'll see that this id is now exactly

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the same as the one up there.

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So I did not actually change the immutable value. I simply changed the variable

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to refer to a different object.

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This is an important distinction, and it's one that may take a while for you

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to get your head around, but we'll cover some of those as we get into this in more detail.

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There will be times when something that you want to do, like change the value of

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a string or to insert objects in a tuple, you may find that you need to use a

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different type, a mutable type instead of an immutable type, in order to be able

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to accomplish where it is you are trying to accomplish.

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In fact, most fundamental types in Python are immutable. Numbers, strings, and

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tuples are the fundamental types that are immutable.

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Mutable objects include lists, dictionaries and some other objects, depending

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upon their implementation.

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So as you create your code in Python, simply be aware that there are some

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types that are immutable -

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and these are typically the more fundamental types - and other types that are mutable.

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And as we get into the details of these types, we'll talk about the things you

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can and cannot do with mutable and immutable objects.