Below a small example of Python in case you have single part features (use the Multipart To Singlepart—Help | ArcGIS for Desktop tool). I digitized some roads and buffered them:
After running the Multipart to Singlepart tool I ended up with two features. When I run the code below (creating a new featureclass, not overwriting the input geometries), I end up with this:
Code used:
def main():
import arcpy
fc = r'D:\Xander\GeoNet\EliminateHoles\gdb\data.gdb\roads_buf_sp'
fc_out = r'D:\Xander\GeoNet\EliminateHoles\gdb\data.gdb\result01'
sr = arcpy.Describe(fc).spatialReference
lst_feats = []
with arcpy.da.SearchCursor(fc, ('SHAPE@')) as curs:
for row in curs:
polygon = row[0]
polyline = polygon.boundary()
first_part = polyline.getPart(0)
polygon_new = arcpy.Polygon(first_part, sr)
lst_feats.append(polygon_new)
arcpy.CopyFeatures_management(lst_feats, fc_out)
if __name__ == '__main__':
main()