I can't remember which version of RxPY I installed and the obvious does not seem to work:
In[33]: import rx
In[34]: rx.__version__
Traceback (most recent call last):
  File "C:\Program Files\Python\2.7\lib\site-packages\IPython\core\interactiveshell.py", line 3035, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-34-b9c56e77da3a>", line 1, in <module>
    rx.__version__
AttributeError: 'module' object has no attribute '__version__'
In[35]: any(map(lambda x: 'version' in x.lower(), dir(rx)))
Out[35]: False
Edit
Also, help doesn't contain the version:
In[38]: help(rx)
Help on package rx:
NAME
    rx
FILE
    c:\Program Files\python\2.7\lib\site-packages\rx\__init__.py
PACKAGE CONTENTS
    abstractobserver
    anonymousobservable
    anonymousobserver
    autodetachobserver
    backpressure (package)
    blockingobservable
    checkedobserver
    concurrency (package)
    disposables (package)
    internal (package)
    joins (package)
    linq (package)
    notification
    observable
    observeonobserver
    observer
    scheduledobserver
    subjects (package)
    testing (package)
DATA
    Future = None
    asyncio = None
    config = {'Future': None, 'Lock': <function RLock>, 'asyncio': None}
 
                        
If you are using
pipthen just runpip list.This will show you the installed packages and their versions.
You are looking for a package called
Rx. You could combine withgrep(depending on OS / Shell). See screenshot below: