What are literals in python? [duplicate]

Question

What exactly is a literal in python? I searched for the answer on google, and in the python docs, but google just references to string literals, and the python docs don't explicitly state what a literal is. I came across this page http://www.dalkescientific.com/writings/NBN/python_intro/literals.html that provided the following answer:

Objects are also called data structures. Python comes with some built-in objects. Some are used so often that Python has a quick way to make these objects, called literals. The literals include the string, unicode string, integer, float, long, list, tuple and dictionary types.

Is this correct? Can I assume that literals are just another term for python's built-in objects? Are there any more literals that were not covered in the description? I was under the impression that there was such a thing as a binary literal, and that booleans were also considered literals.

Answer 1

A literal is something that the parser recognizes as syntax for writing an object directly. Some examples in Python 2:

• 0, 1, 2, 3 (int literals)
  • -1, -2, etc are not literals themselves, but expressions involving the unary - operator.
• 5j, 3.14j (non-negative pure imaginary complex literals)
  • Other complex values, like 2+3j, 2-3j, and -5j, are expressions involving various operators.
• 3.5, -2.7 (float literals)
• "", "hello" (str literals)
• u"", u"hello" (unicode literals)
• None (I think this is considered a literal, and not a keyword or simple name.)

Other literal-like expressions called displays are used to create various containers. They aren't true literals because they can contain non-literal expressions (e.g., [x, y]).

• [], [1,2] (list displays)
• (), (1,), (1,2) (tuple displays)
• {}, {'a': 2} (dict displays)
• {1,2,3} (set display introduced in Python 2.7)

There is no literal or display for an empty set, as the obvious notation {} is already a dict display. Python 2 does not have true Boolean literals; True and False are simply built-in names for the Boolean objects. A tuple is technically created by the comma, and the parentheses are only necessary when you need to disambiguate the expression; the exception is the empty tuple ().

See phihag's answer for some differences in Python 3.