Using update to initialize an empty array property fails

[jonmmease]

From #1050

Looks like there's a little more to this one - I also can't use update for layout.shapes even with Plotly 3.1.0. The following code prints an empty tuple.

import plotly.graph_objs as go
layout = go.Layout()
shapes = [
    # Line Vertical
    {
        'type': 'line',
        'x0': 1,
        'y0': 0,
        'x1': 1,
        'y1': 2,
        'line': {
            'color': 'rgb(55, 128, 191)',
            'width': 3,
        },
    },
    # Line Horizontal
    {
        'type': 'line',
        'x0': 2,
        'y0': 2,
        'x1': 5,
        'y1': 2,
        'line': {
            'color': 'rgb(50, 171, 96)',
            'width': 4,
            'dash': 'dashdot',
        },
    },
    # Line Diagonal
    {
        'type': 'line',
        'x0': 4,
        'y0': 0,
        'x1': 6,
        'y1': 2,
        'line': {
            'color': 'rgb(128, 0, 128)',
            'width': 4,
            'dash': 'dot',
        },
    },
]
layout.update(shapes=shapes)
print(layout.shapes)

[jonmmease]

Legacy (version 2.7) behavior:

1. If the original layout.shapes property is uninitialized, then the shapes variable is used to initialize the property:

from pprint import pprint
import plotly.graph_objs as go

layout = go.Layout()
shapes = [
    # Line Vertical
    {
        'type': 'line',
        'x0': 1,
        'y0': 0,
        'x1': 1,
        'y1': 2,
        'line': {
            'color': 'rgb(55, 128, 191)',
            'width': 3,
        },
    },
    # Line Horizontal
    {
        'type': 'line',
        'x0': 2,
        'y0': 2,
        'x1': 5,
        'y1': 2,
        'line': {
            'color': 'rgb(50, 171, 96)',
            'width': 4,
            'dash': 'dashdot',
        },
    },
    # Line Diagonal
    {
        'type': 'line',
        'x0': 4,
        'y0': 0,
        'x1': 6,
        'y1': 2,
        'line': {
            'color': 'rgb(128, 0, 128)',
            'width': 4,
            'dash': 'dot',
        },
    },
]
layout.update(shapes=shapes)
pprint(layout.shapes)

[{'line': {'color': 'rgb(55, 128, 191)', 'width': 3},
  'type': 'line',
  'x0': 1,
  'x1': 1,
  'y0': 0,
  'y1': 2},
 {'line': {'color': 'rgb(50, 171, 96)', 'dash': 'dashdot', 'width': 4},
  'type': 'line',
  'x0': 2,
  'x1': 5,
  'y0': 2,
  'y1': 2},
 {'line': {'color': 'rgb(128, 0, 128)', 'dash': 'dot', 'width': 4},
  'type': 'line',
  'x0': 4,
  'x1': 6,
  'y0': 0,
  'y1': 2}]

2. If the original layout.shapes property is initialized to a list of length N, then the properties of the first N elements of the shapes variable are merged in. Elements beyond N are ignored.

layout2 = go.Layout(shapes=[{'line': {'dash': 'dot'}}])
layout2.update(shapes=shapes)
pprint(layout2.shapes)

[{'line': {'color': 'rgb(55, 128, 191)', 'dash': 'dot', 'width': 3},
  'type': 'line',
  'x0': 1,
  'x1': 1,
  'y0': 0,
  'y1': 2}]

3. If the original layout.shapes property is an empty list, then N is zero and so the entire shapes variable is ignored

layout3 = go.Layout(shapes=[])
layout3.update(shapes=shapes)
pprint(layout3.shapes)

[]

In plotly.py version 3, what used to be case 1 is now falling into case 3. So we just need to check for the difference between an uninitialized shapes property and an empty shapes property.