How does the u and r prefixes work with strings in python?

Question

I know that we can use the r(raw string) and u(unicode) flags before a string to get what we might actually desired. However, I am wondering how these do work with strings. I tried this in the IDLE:

a = r"This is raw string and \n will come as is"
print a
# "This is raw string and \n will come as is"
help(r)
# ..... Will get NameError
help(r"")
# Prints empty

How Python knows that it should treat the r or u in the front of a string as a flag? Or as string literals to be specific? If I want to learn more about what are the string literals and their limitations, how can I learn them?

Answer 1

The u and r prefixes are a part of the string literal, as defined in the python grammar. When the python interpreter parses a textual command in order to understand what the command does, it reads r"foo" as a single string literal with the value "foo" . On the other hand, it reads b"foo" as a single bytes literal with an equivalent value.

For more information, you can refer to the literals section in python's documentation. Also, python has an ast module, that allows you to explore the way python parses commands.