在Python 3.X中具有相同名称的类型和函数？

Question

As I understand there are no declaration types in Python. When you need an integer or list you would do:

integer = 5
list_of_integers = [0, 1, 2]

This link to the documentation tells me that int in Python is a built-in function.

I'm aware of functions such as str() and int() to convert an integer to string and vice-versa.

But I have never seen a use of int as a type with dot notation Eg *int.[function_name]*

How come it can be both a type and a function with the same name? Are there other types such as float , double , and etc. which can be used with dot notation and as well as a function?

Answer 1

int and str are classes . As with any class in Python, calling it gives you an instance. And as with any instance, you certainly can call methods on it. int doesn't have that many user-callable methods, but str certainly does: some of the common ones include strip , split , upper , etc.

>>> x = str()
>>> x.upper()
''

Edit

It's still a class. You can do exactly the same with any class, even ones you define yourself:

>>> class Foo(object):
...   def bar(self):
...     print self.baz
...
>>> f=Foo()
>>> f.baz = 'quux'
>>> f.bar()
quux
>>> Foo.bar(f)
quux

The last operation here is exactly the same idea as calling str.upper(x)

Answer 2

int and str aren't functions. They are basically data types which in python are actually classes containing different functions of their own. That's why you can convert an integer to a string using the str(int) method but you can't do the same with int(string) to convert a string to an integer. And as these are classes one can say that there are different functions (methods) in the class which are in turn use with the dot notation.