handing Null return in rpy2
Question: I am using rpy2 to call R function from python.

    
    
    from rpy2.robjects import *
    result=r.someFunctioninR()   #someFunctioninR is a R function written by myself
    if result==r('as.null()'):
         do something
    else:
         do something else
    

The "result" returned by someFunctioninR() can be either NULL or other format.
result==r('as.null()') does not work. Is there any other way I can get a True
when result is NULL?


Answer: Try `rpy2.rinterface.NULL` or `robj.r("NULL")`:

    
    
    In [1]: from rpy2 import robjects as robj
    

Create an R function that returns NULL:

    
    
    In [2]: robj.r("nullfn = function(){NULL}")
    Out[2]: <SignatureTranslatedFunction - Python:0x104ea5ef0 / R:0x1058be4a8>
    
    In [3]: result = robj.r.nullfn()
    
    In [4]: print result
    NULL
    
    In [5]: print result == robj.rinterface.NULL
    True
    
    In [6]: print result == None
    False
    

**edit** : I just realized that your code above should work as is. I think
your error is probably due to the return type of r.someFunctionInR() -- is it
possible it's returning a vector of NULL values? Have you tried printing the
value of `result`? If this doesn't work, you might share what
`someFunctionInR()` is.

