Print a line/multiline in a new layer over a map using Folium

Some of the functions in the earlier example are now deprecated; apparently, the preferred method is now something like:

import folium

# Coordinates are 10 points on the great circle from Boston to
# San Francisco.
# Reference: http://williams.best.vwh.net/avform.htm#Intermediate
coordinates = [
    [42.3581, -71.0636],
    [42.82995815, -74.78991444],
    [43.17929819, -78.56603306],
    [43.40320216, -82.37774519],
    [43.49975489, -86.20965845],
    [41.4338549, -108.74485069],
    [40.67471747, -112.29609954],
    [39.8093434, -115.76190821],
    [38.84352776, -119.13665678],
    [37.7833, -122.4167]]

# Create the map and add the line
m = folium.Map(location=[41.9, -97.3], zoom_start=4)
my_PolyLine=folium.PolyLine(locations=coordinates,weight=5)
m.add_child(my_PolyLine)
# m.save('line_example_newer.html')

Neither of the above worked for me for adding lines as a new layer to a folium.Map object (using folium 0.11). What works for me is using folium.FeatureGroup:

coords = [[[42.3554025, -71.0728116], [42.3554142, -71.0728438]],
 [[42.3554142, -71.0728438], [42.3554296, -71.0728738]]]
test_map = folium.Map([42.3554025, -71.0728116], tiles='Cartodb Positron', zoom_start=15)
fg = folium.FeatureGroup("Lines")
folium.PolyLine(coords).add_to(fg)
f.add_to(test_map)
folium.LayerControl(position='bottomright').add_to(test_map)
test_map

This prints a map that has a "Lines" layer which, when toggled, will show the lines plotted at the coordinates above.

I finally found a way implemented in Folium in January 2014 and not documented. Its the line method.

Here appears an example provided by the author of this addon.