double-underscore

I'm fairly new to actual programming languages, and Python is my first one. I know my way around Linux a bit, enough to get a summer job with it (I'm still in high school), and on the job, I have a lot of free time which I'm using to learn Python. One thing's been getting me though. What exactly is different in Python when you have expressions such as x.__add__(y) <==> x+y x.__getattribute__('foo') <==> x.foo I know what methods do and stuff, and I get what they do, but my question is: How are those double underscore methods above different from their simpler looking equivalents? P.S., I don't

I was having a look through some open source C++ code and notice a lot of double under scores where used in the code, mainly at the start of variable names. return __CYGWIN__; Just wondering is there a reason for this, or is it just some people code styles? I would think that I makes it hard to read. From Programming in C++, Rules and Recommendations : The use of two underscores (`__') in identifiers is reserved for the compiler's internal use according to the ANSI-C standard. Underscores (`_') are often used in names of library functions (such as "_main" and "_exit"). In order to avoid