Using Python to field calculate Lat/Long with decimal degrees rather than meters

As stated in the tool documentation for Calculate Field:

Python expressions can use the geometry area and length properties with an areal or linear unit to convert the value to a different unit of measure (for example, !shape.length@kilometers!)

These expressions are not usable with points or individual coordinates. Fortunately, you can use other properties and methods of the pointGeometry and point classes to get your desired result.

Since your data is already in a geographic coordinate system, the following will return latitude and longitude values of your points. (Technically this returns the coordinates of the first part of each point, but that's only relevant if you are using MultiPoint geometry).

!SHAPE!.firstPoint.X #Longitude
!SHAPE!.firstPoint.Y #Latitude

If your data were in a different coordinate system, the following field calculator expressions convert each point to a PointGeometry object and then use the projectAs to project each point to the WGS84 geographic coordinate system before getting the coordinates. If your data has a datum other than WGS84, you should use the appropriate SpatialReference object constructed using the name or well-known ID of the datum.

arcpy.PointGeometry(!Shape!.firstPoint,!Shape!.spatialReference).projectAs(arcpy.SpatialReference(4326)).firstPoint.X
arcpy.PointGeometry(!Shape!.firstPoint,!Shape!.spatialReference).projectAs(arcpy.SpatialReference(4326)).firstPoint.X

I don't know why it's necessary to create the PointGeometry object instead of just running projectAs on !SHAPE!. On ArcMap 10.3 the !SHAPE! object is <type 'geoprocessing describe geometry object'> while the PointGeometry is <class 'arcpy.arcobjects.geometries.PointGeometry'> in ArcMap 10.3. This is not necessary when using cursors in Python.

I was able to figure it out with a work around. I added the Lat/Long Fields and then us Convert Coordinate Notation. That generated a new feature class with two new fields: DDLat and DDLon. That got me what I needed even though I had to add a couple additional steps. The output was 076.###W, 37.####N as opposed to what I wanted which was (-76.###, 37.####) so I am adding steps now to recalculate the fields to make them into that format and delete the old file etc...

The specific steps that I had to do were:

## Field Calculate
input_FeatureClass = "wPM_Points_Converted"
expression3 = "{0}".format("!DDLat![:-1]") 
expression4 = "{0}".format("!DDLon![1:-1]")
expression5 = "{0}".format("- !Longitude!")

arcpy.CalculateField_management(input_FeatureClass, "Latitude", expression3, "PYTHON_9.3")
print "Latitude Field Calculation Complete"
arcpy.CalculateField_management(input_FeatureClass, "Longitude", expression4, "PYTHON_9.3")
arcpy.CalculateField_management(input_FeatureClass, "Longitude", expression5, "PYTHON_9.3")
print "Longitude Field Calculation Complete"

## Delete fields that were created from Coordinate Notation
arcpy.DeleteField_management(input_FeatureClass,  ["DDLat", "DDLon"])
print "Deleted fields that were created from Coordinate Notation"