In python's OS module there is a method to open a file and a method to read a file.

The [docs](http://docs.python.org/2/library/os.html) for the open method say:

> 
> Open the file file and set various flags according to flags and
>  possibly its mode according to mode. The default mode is 0777 (octal),
>  and the current umask value is first masked out. Return the file
>  descriptor for the newly opened file.
> 
> 
> 

The docs for the read method say;

> 
> Read at most n bytes from file descriptor fd. Return a string
>  containing the bytes read. If the end of the file referred to by fd
>  has been reached, an empty string is returned.
> 
> 
> 

I understand what it means to read n bytes from a file. But how does this differ from open?