The pystack is to python as jstack is to java.
It's a debug tool to print python threads or greenlet stacks.
Idea stolen from pyrasite.
$ pip install pystack-debugger
You may need to run it with
$ sudo pystack [--include-greenlet] <pid>
The pystack is compatible with CPython 2.7+ and CPython 3.6+ in both client (the debugger) and server (the destination process).
Using PyPy may work in client (the debugger) but it is untested. Do not attempt to attach a PyPI process as destination since the pystack debugger uses gdb/lldb to invoke the CPython ABI.