Stream handles and the predefined streams sys.stdin, sys.stdout, sys.stderr

Python, like most languages, treats input and output sources as streams: sequences of data you read from or write to in order. A stream handle is the object your program holds to work with a stream. open() returns one, and all file operations (read, write, close) are methods called on it. The handle also keeps track of the current position in the file, which moves forward as you read or write.