change line opacity, leave markers opaque

Is it possible to add an opacity to the line-attribute?change the line opacity but not the marker opacity? I found that I can set the opacity of the entire line including markers (opacity = .5) and the one of the marker (e.g. marker={"opacity":1}). However, it is seemingly impossible to reduce the opacity of just the line.

As shown in this example:

import plotly
import plotly.graph_objs as go
plotly.offline.init_notebook_mode(connected=True)  # I'm running in a jupyter notebook

x = np.arange(0,10)
ys = [np.random.rand(10) for _ in range(3)]

lines = []
for y in ys:
    line = go.Scatter(x=x, y=y, mode="markers+lines", opacity=.5, marker={'symbol': 'x', 'size': "15", "opacity":1},
        line={'opacity': 0.5}
    )
    lines.append(line)           
fig = go.Figure(
    data=lines,
    layout=go.Layout(showlegend=True)
)
plotly.offline.iplot(fig)

See result here:

My problem is the following: My data points are important, the lines are just visual aid. I want to make the lines .5-opaque but have the markers fully opaque.
However, when I set opacity=.5, marker={'opacity':1} the opacity of the marker is also reduced. (I believe that the marker-opacity is defined in the range [0, line-opacity].

PS: If there is an existing solution/workaround for this issue, it might be interesting to (also) answer on my post on Stackoverflow

[hidai]

I have the same use-case. Any plan to address the original issue (adding line.opacity)?

[raffg]

+3

My use case is the bottom right chart here https://covid-19-raffg.herokuapp.com/

Workaround is this:

def hex_to_rgba(h, alpha):
    '''
    converts color value in hex format to rgba format with alpha transparency
    '''
    return tuple([int(h.lstrip('#')[i:i+2], 16) for i in (0, 2, 4)] + [alpha])


import pandas as pd
import plotly
import plotly.graph_objects as go
trace_data = pd.DataFrame({'base': [0, 1, 2, 3, 4],
                           'trace1': [1, 2, 3, 4, 5],
                           'trace2': [1.5, 1.9, 2, 3.9, 6],
                           'trace3': [2, 1, 3.3, 4.4, 4.5],
                           'trace4': [0, 3, 2, 1, 3]})

trace_colors = plotly.colors.qualitative.D3
color_idx = 0

fig = go.Figure()
for trace in ['trace1', 'trace2', 'trace3', 'trace4']:
    marker_size = [0] * (len(trace_data) - 1)
    marker_size.append(6)
    color = trace_colors[color_idx % len(trace_colors)]
    marker_color = 'rgba' + str(hex_to_rgba(color, 1))
    line_color = 'rgba' + str(hex_to_rgba(color, .25))
    # Perform a lot of data wrangling in Pandas here...
    fig.add_trace(go.Scatter(x=trace_data['base'],
                             y=trace_data[trace],
                             mode='lines+markers',
                             marker=dict(color=marker_color,
                                         size=marker_size),
                             line=dict(color=line_color, width=1),
                             name=trace))
    color_idx += 1
fig.show()