[BUG] folium.GeoJson() with style_function changes input data

Please add a code sample or a nbviewer link, copy-pastable if possible

Example data:

pistes = {"features":[{'geometry': {'coordinates': [[13.7750875, 47.3894653],
     [13.7745458, 47.3897487],
     [13.7744245, 47.3899024],
     [13.7743022, 47.3901266],
     [13.7742754, 47.3904393],
     [13.7745857, 47.3913728],
     [13.7747696, 47.3922164]],
    'type': 'LineString'},
   'properties': {'difficulty': 'easy'},
   'type': 'Feature'},
  {'geometry': {'coordinates': [[13.7748277, 47.3951473],
     [13.7745382, 47.3955505],
     [13.7740868, 47.3961718],
     [13.7738771, 47.3965048],
     [13.7739069, 47.3967489],
     [13.77409, 47.3970407],
     [13.7744923, 47.3973698],
     [13.7748859, 47.3977331],
     [13.7753385, 47.3980947],
     [13.7756779, 47.3983777],
     [13.7758294, 47.3985963],
     [13.7758483, 47.3987251],
     [13.7758303, 47.3988537]],
    'type': 'LineString'},
   'properties': {'difficulty': 'advanced'},
   'type': 'Feature'},
  {'geometry': {'coordinates': [[13.7750875, 47.3894653],
     [13.7752798, 47.38999],
     [13.7753808, 47.3905846],
     [13.7754171, 47.391452],
     [13.7754382, 47.3919579],
     [13.7751964, 47.3927863],
     [13.7759708, 47.3937253],
     [13.7764045, 47.3944936],
     [13.7766345, 47.3947044],
     [13.7774691, 47.3955802],
     [13.7775424, 47.3958695],
     [13.7773201, 47.3963544],
     [13.7770295, 47.3965058],
     [13.777536, 47.3973757]],
    'type': 'LineString'},
   'properties': {'difficulty': 'intermediate'},
   'type': 'Feature'}]}

Example:

m = folium.Map(location=[47.4, 13.78],tiles='OpenStreetMap',zoom_start=14)

diff_to_colour = {'easy':'blue', 'intermediate':'red','advanced':'black'}
def piste_style_function(feature):
    return {'opacity': 1, 
            'weight': 1, 
            'color': diff_to_colour[feature['properties']['difficulty']]}

folium.GeoJson(pistes, style_function=piste_style_function).add_to(m)
m

Then, in a separate notebook cell (after map rendered):

pistes

{'features': [{'geometry': {'coordinates': [[13.7750875, 47.3894653],
     [13.7745458, 47.3897487],
     [13.7744245, 47.3899024],
     [13.7743022, 47.3901266],
     [13.7742754, 47.3904393],
     [13.7745857, 47.3913728],
     [13.7747696, 47.3922164]],
    'type': 'LineString'},
   'properties': {'difficulty': 'easy',
    'highlight': {},
    'style': {'color': 'blue', 'opacity': 1, 'weight': 1}},
   'type': 'Feature'},
  {'geometry': {'coordinat 
...

Notice the additional style property.

Problem description

The style function should NOT edit the data in place. This become problematic in the following cases:

• You want to re-use a pre-filtered collection of features
• You want to use several layers (where you tweak styles)

Expected Output

Unchanged pistes

Output of folium.__version__

‘0.5.0’

[arkanoid87]

been wasting hours on this and still I’ve not solved the problem

I’m adding more layers using a loop function over the target_col variable

            style_function=lambda feature: {
                'fillOpacity': 0.5,
                'weight': 0.5,
                'color': "#8b0000" if feature['properties'][target_col] > -1 else "#808080",
                'fillColor': colorscale(feature['properties'][target_col]) if feature['properties'][target_col] > -1 else "#d4d4d4"
            },

I always get TypeError: '>' not supported between instances of 'NoneType' and 'int' on m.save(…) on the second feature of the second layer added.

Everything works if I loop over the target_col only once, it always returns error on second layer even if I set global constant geodataframe in input, even when passing a fresh copied database in input.

Very frustrating

[Conengmo]

Hi @arkanoid87 , this issue you are replying to is no longer relevant, we no longer change the input data in recent folium versions. I suggest you double check you input data. If you really think the issue lies with folium, please open a new ticket and provide a minimal, self-contained example that will help us debug the issue.