Import Modules in Nifi ExecuteScript
The "python" engine used by ExecuteScript and InvokeScriptedProcessor is actually Jython, not pure Python. This means it cannot load native modules (.so files, compiled C files, etc.). According to this SO post, paramiko uses Crypto which has native libraries, so cannot be used in Jython (see the bottom of this post for my comment on that). My guess is that the sftp library does the same.
Jython can make use of pure Python modules, there is a discussion on the NiFi mailing list about how to point at (and include) those kinds of modules.
ExecuteScript processor uses its own Jython Engine to execute your python scripts. As the libraries which you are importing are not available in NIFI inbuild Jython Engine its throwing error.
SOLUTION:
If python is already installed on our machine with all those libraries (the same machine where your NIFI is installed) you can use that python engine to execute your script. you can execute your python code using ExecuteProcess processor. see the configuration of ExecuteProcess.