'exit' is not a keyword in Python, but no error occurs while using it

Question

I learn that exit is not a keyword in Python by,

import keyword
print('exit' in keyword.kwlist)     # Output: False

But there is no reminder of NameError: name 'exit' is not defined while using it. The output of the following snippet code makes me confused. Can anyone help me out?

for i in range(5):
    print(i)
    cur=i if i<2 else exit

print(cur)
# Output
0
1
2
3
4
Use exit() or Ctrl-D (i.e. EOF) to exit

I am unable to get related info about exit from Python documentations, except for exit([code=None]).

Answer 1

Keywords are part of the python syntax. They usually have special meaning in statements (e.g. for, del, if ...). This has other consequences -- e.g. you can't make a variable with the same name as a keyword.

builtins are callable objects (e.g. functions or at least function-like) that python provides in the namespace by default. examples of builtin functions are things like sorted, id, vars, ...

It's worth noting that exit is a convenience provided when in an interactive session. It's highly encouraged to use sys.exit instead.

Answer 2

exit is an instance of the Quitter class. The Quitter class defines an __repr__ method that returns the string that you see when you type exit into the shell. It also defines a __call__ method. Just as __init__ is called when you use a class like a function, __call__ is called when an instance is used like a function. Therefore, exit() calls the __call__ method, which exits the program.