What's Python's equivalent to Java InputStream's available method?
You've got to tell us what type of object you're working with.  I'm assuming you're talking about a socket read.  Either you read the socket with blocking or you read without blocking.  You can measure how you have just read in a non-blocking read, if you are interested in that.  However, it sounds like you are trying to bend python into a java.io style stream-buffer paradigm that it just doesn't support in detail.
Java's InputStream provides a method named available which returns the number of bytes that can be read without blocking. 
How can I achieve this in Python?