Is everything an object in python like ruby?

问题

A comment on another Stack Overflow question states that Python was just like Ruby, as it relates to \"everything\'s an object,\" and everything in Python was an object, just like Ruby.

Is this true? Is everything an object in python like ruby?

How are the two different in this respect or are they really the same? For example, can you take a number and do the ruby stuff I\'ve seen like:

y = 5.plus 6

Can that be done the same way in Python?

回答1:

DiveIntoPython - Everything Is an Object

Everything in Python is an object, and almost everything has attributes and methods. All functions have a built-in attribute __doc__, which returns the doc string defined in the function's source code. The sys module is an object which has (among other things) an attribute called path. And so forth.

Still, this begs the question. What is an object? Different programming languages define “object” in different ways. In some, it means that all objects must have attributes and methods; in others, it means that all objects are subclassable. In Python, the definition is looser; some objects have neither attributes nor methods (more on this in Chapter 3), and not all objects are subclassable (more on this in Chapter 5). But everything is an object in the sense that it can be assigned to a variable or passed as an argument to a function (more in this in Chapter 4).

Ruby Docs - To Ruby From Python

As with Python, in Ruby,... Everything is an object

So there you have it from Ruby's own website: in Python everything is an object.

回答2:

While everything is an object in Python, it differs from Ruby in its approach to resolving names and interacting with objects.

For example, while Ruby provides you with a 'to_s' method on the Object base class, in order to expose that functionality, Python integrates it into the string type itself - you convert a type to a string by constructing a string from it. Instead of 5.to_s, you have str(5).

Don't be fooled, though. There's still a method behind the scenes - which is why this code works:

(5).__str__()

So in practice, the two are fundamentally similar, but you use them differently. Length for sequences like lists and tuples in Python is another example of this principle at work - the actual feature is built upon methods with special names, but exposed through a simpler, easier-to-use interface (the len function).

The python equivalent to what you wrote in your question would thus be:

(5).__add__(6)

The other difference that's important is how global functions are implemented. In python, globals are represented by a dictionary (as are locals). This means that the following:

foo(5)

Is equivalent to this in python:

globals()["foo"].__call__(5)

While ruby effectively does this:

Object.foo(5)

This has a large impact on the approach used when writing code in both languages. Ruby libraries tend to grow through the addition of methods to existing types like Object, while Python libraries tend to grow through the addition of global functions to a given module.

回答3:

"everything" is a tad of an overbid, for both Python and Ruby -- for example, if is not "an object", rather it's a keyword used to start a conditional statement or (in Python) inside list comprehensions and generator expressions. The enthusiasm of finding out that functions, classes, methods, and all sort of such things that aren't really objects in (say) C++, are objects in Ruby or Python, causes such enthusiasm. Other things may be objects in Ruby but not Python or viceversa (code blocks, regular expressions, ...).

回答4:

In answer to your second question, yes:

>>> (1).__add__(2)
3

回答5:

Yep, as far as I know everything is an object in Python. Certainly the primitive and builtin types (int, long, str, float, etc.) can be subclassed - and in fact the types themselves are objects. Functions are objects, classes are objects, even code blocks are objects in a sense... I can't think of anything in Python that can't be treated as an object.

回答6:

To add a comment to other people's excellent answers: everything is an object, but some – notably strings and numeric types – are immutable. This means that these types behave the way they do in languages like C or Java (where integers, etc. are not objects) with respect to assignment, parameter passing, etc, and you never have to worry about traps caused by pass-by-reference. It's rather a good solution :-)

来源：https://stackoverflow.com/questions/865911/is-everything-an-object-in-python-like-ruby