Stream Objects From Non-File Sources

Imagine you’re writing a library, and one of your library functions is going to read some data from a file. The function could simply take a filename as a string, go open the file for reading, read it, and close it before exiting. But you shouldn’t do that. Instead, your api should take an arbitrary stream object.

In the simplest case, a stream object is anything with a read() method which takes an optional size parameter and returns a string. When called with no size parameter, the read() method should read everything there is to read from the input source and return all the data as a single value. When called with a size parameter, it reads that much from the input source and returns that much data. When called again, it picks up where it left off and returns the next chunk of data.

To read from a fake file, just call read().

That sounds exactly like the stream object you get from opening a real file. The difference is that you’re not limiting yourself to real files. The input source that’s being “read” could be anything: a web page, a string in memory, even the output of another program. As long as your functions take a stream object and simply call the object’s read() method, you can handle any input source that acts like a file, without specific code to handle each kind of input.