Question

In python I can do things like:

d = dict()
i = int()
f = float()
l = list()

but there is no constructor for strings

>>> s = string()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'string' is not defined

Why is that? Or, IS there a constructor for string types?

Also, following the definitions above,

d['a'] = 1

works, but

>>> l[0] = 1
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IndexError: list assignment index out of range

does not.

Can someone explain this to me?

Answer 1

As others have noted, you want str, not string.

But to answer your other question, lists cannot be extended by assignment. If you try to assign outside the bounds of a list, you get an error. On the other hand, dictionaries have no bounds in any meaningful sense; they have only defined keys and undefined keys.

Think of a dictionary as a bag of objects tied together, and a list as a tray with a fixed number of compartments. You can throw a pair of things into the bag anytime, but you can’t put something in a tray’s compartment if no such compartment exists. You have to create the compartment, using append or something similar. Since your “tray” has no compartments yet, l[0] = x fails.