Python Blueprint duplicate Logs
Your problem is almost certainly that you have set up 5 different logging handlers as well as 5 different loggers.  Python's built-in logging system is a hierarchical logging system (unlike the normal loggers built for NodeJS, for example).  All the loggers form a tree at run time, and the log messages bubble up the tree and are handled by the handlers attached to the tree.  The normal handler registration registers the handlers at the root of the tree, so each handler sees messages from every logger (which is why your messages are created five times).
The solution is to create one logger per blueprint, but not register any handler for the blueprint's logger.  Instead, register one handler at the application level.
I have 5 Flask apps which are running under Blueprint. Each app has its independent logger which writes to stdout. The problem is whenever any HTTP API is invoked, the log in that API is printed on screen 5 times, but the request is executed only once. How do I fix logger, so that each requested is printed only once ? 
Python 2.7.10
Flask 0.10.1