Iterating through rows and saving result in a new column

[kiton]

Hello everyone! I am seeking your help on the following task.

So, thankfully to you I was able to extract geo coordinates from a tweet, and save latitude/longitude as float64 in separate columns. Now, I need to convert coordinates to FIPS codes. The easiest way seems to be using -stateplane-:

import stateplane
stateplane.identify(-78.873165, 39.207769, fmt='fips') # lon first
'4701'

To create a new column with identifed FIPS code, I do the following:

for index, row in df.iterrow():
     df["FIPS"] = df[stateplane.identify('lon', 'lat', fmt='fips')]

But I guess I am doing it incorrectly -- i.e., specifying lon/lat columns to get values from, as I get the following error:

Error:
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
/Users/mymac/anaconda/lib/python3.6/site-packages/shapely/geometry/point.py in geos_point_from_py(ob, update_geom, update_ndim)
    201         # From array protocol
--> 202         array = ob.__array_interface__
    203         assert len(array['shape']) == 1

AttributeError: 'tuple' object has no attribute '__array_interface__'

During handling of the above exception, another exception occurred:

TypeError                                 Traceback (most recent call last)
<ipython-input-20-e8453e36b340> in <module>()
      1 for index, row in test.iterrows():
----> 2     text["FIPS"] = stateplane.identify('lon', 'lat', fmt='fips') # lon then lat

/Users/mymac/anaconda/lib/python3.6/site-packages/stateplane/stateplane.py in identify(lon, lat, fmt, statefp, countyfp)
     83     '''
     84 
---> 85     result = _id(lon, lat, statefp=statefp, countyfp=countyfp)
     86 
     87     try:

/Users/mymac/anaconda/lib/python3.6/site-packages/stateplane/stateplane.py in _id(lon, lat, statefp, countyfp)
     63         raise ValueError("SPCS not found for statefp={}".format(statefp))
     64 
---> 65     target = Point(lon, lat)
     66     result = None
     67 

/Users/mymac/anaconda/lib/python3.6/site-packages/shapely/geometry/point.py in __init__(self, *args)
     47         BaseGeometry.__init__(self)
     48         if len(args) > 0:
---> 49             self._set_coords(*args)
     50 
     51     # Coordinate getters and setters

/Users/mymac/anaconda/lib/python3.6/site-packages/shapely/geometry/point.py in _set_coords(self, *args)
    127             self._geom, self._ndim = geos_point_from_py(args[0])
    128         else:
--> 129             self._geom, self._ndim = geos_point_from_py(tuple(args))
    130 
    131     coords = property(BaseGeometry._get_coords, _set_coords)

/Users/mymac/anaconda/lib/python3.6/site-packages/shapely/geometry/point.py in geos_point_from_py(ob, update_geom, update_ndim)
    233             coords = ob
    234         n = len(coords)
--> 235         dx = c_double(coords[0])
    236         dy = c_double(coords[1])
    237         dz = None

TypeError: must be real number, not str

Please advise how to do it right.