In Python, all literal values result in the creation of objects

Question

What does this mean "In Python, all literal values result in the creation of objects"?

I am learning Python, and got this sentence from here: http://python4java.necaiseweb.org/Fundamentals/FunctionsAndMethods

But I does not really understand its meaning.

First, what are "literal values"?

Second, please explain this sentence.

If you could make some examples, that would be helpful!

Answer 1

Python actually has a few definitions for "literal" in different contexts, but if you just want the basic idea: Numbers like 123 and strings like "abc" are literals; expressions like 123 + 456 are not.

In Java, when you write 123, that's not a reference to a Java object, it's a "native" integer. In Python, it is a reference to a Python object.

Because everything is an object in Python, an integer has methods, can be stuck in collections, etc. There's no "boxing" and "unboxing" anywhere. If I want to stick 123 into a list, I just do it:

>>> my_list = list()
>>> my_list.append(123)
>>> my_list
[123]

And if I want to use the value from the list as an integer, I just do it:

>>> my_list[0] - 120
3

For that matter, I can just write a list display, using literals just like other objects:

>>> my_other_list = [my_list, 2]

(Just don't ask whether a list display is also a literal, because that's when the "different definitions for different contexts" actually matters…)

---

It's worth pointing out that it's not really true that "all literal values result in the creation of objects". A literal may be a new object, but it may also be a reference to existing object with the same value that. For example:

>>> a = 3
>>> b = 3
>>> a is b
True
>>> id(a) == id(b)
True

(This isn't guaranteed to be true by the language, but it usually will be on most Python implementations.)

So, b = 3 did not result in the creation of an object, just another reference to the same object in a = 3. (And in fact, that 3 was most likely already pre-built and pre-cached by the interpreter before even looking at your code.)

But you don't need to care about this, because 3 is immutable. It doesn't matter if you get the same 3 object or a different one because, short of is and id, there is no way to tell the difference. And the same is true for strings, floats, etc.

Answer 2

The following are examples of literal values

>>> 0
0
>>> 'a'
'a'
>>> 1.9
1.9
>>> 'foo'
'foo'

Everything is an object, even ints, as shown below you can see the methods of 0:

>>> dir(0)
['__abs__', '__add__', '__and__', '__class__', '__cmp__', '__coerce__', '__delattr__', '__div__', '__divmod__', '__doc__', '__float__', '__floordiv__', '__format__', '__getattribute__', '__getnewargs__', '__hash__', '__hex__', '__index__', '__init__', '__int__', '__invert__', '__long__', '__lshift__', '__mod__', '__mul__', '__neg__', '__new__', '__nonzero__', '__oct__', '__or__', '__pos__', '__pow__', '__radd__', '__rand__', '__rdiv__', '__rdivmod__', '__reduce__', '__reduce_ex__', '__repr__', '__rfloordiv__', '__rlshift__', '__rmod__', '__rmul__', '__ror__', '__rpow__', '__rrshift__', '__rshift__', '__rsub__', '__rtruediv__', '__rxor__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__truediv__', '__trunc__', '__xor__', 'bit_length', 'conjugate', 'denominator', 'imag', 'numerator', 'real']

If I want I can call:

>>> (-1).__abs__() # abs(-1) is better but this is just to show it's an object
1