Possible Duplicate:
accessing a python int literals methods
In Python, everything is an object.
But then again, why doesn't the following snippet work?
1.__add__(2)
However, this does work:
n = 1
n.__add__(2)
What is the difference between n and 1?
Isn't it a design failure that it doesn't work?
For instance, it does work with string literals as well.
"one".__add__("two")
For comparison, it works well on other purely object oriented languages too.
Let's take a closer look at this compiling c# example:
Console.WriteLine(100.ToString());
Then again, what distinguishes Python from C# in the perspective of everything is an object?
Python's parser is deliberately very simple - one of the constraints it enforces on itself is that, to figure out what a token means, it can only look one token to the right (it is an LL(1) parser).
So, it sees [number][dot], and determines that it is a floating point literal. '_' isn't a valid character to have in a floating point literal, so it gives a syntax error.
The most obvious and most common way to overcome this is to put the number in parentheses:
(1).__add__(2)
This forces it to interpret the 1 as an integer literal, and the dot as attribute access, within the limitations of the parser.
Another interesting workaround is this:
>>> 1 .__add__(2)
3
That is, add a space before the .. It turns out that Python always allows a space there for any attribute lookup:
>>> range(4) .count(3)
1
I found this quite surprising, but it seems that Python treats . under similar rules to +, and so will allow as much space as you like around it.
Python interprets 1. as float so you have to add parens:
>>> (1).__add__(2)
3
or space:
>>> 1 .__add__(2)
3
If you want float value here just put 2 dots.
>>> 1..__add__(2) #float
3.0
来源：https://stackoverflow.com/questions/12025531/why-does-1-add-2-not-work-out