provide hovermode compare

[eromoe]

I want hover a position show all data accross vertical line, like :

I found javascript version have this plotly/plotly.js#2155 (comment)

But hovermode='compare' got error

ValueError: 
    Invalid value of type 'builtins.str' received for the 'hovermode' property of layout
        Received value: 'compare'

    The 'hovermode' property is an enumeration that may be specified as:
      - One of the following enumeration values:
            ['x', 'y', 'closest', False]

PS: I really think bokeh's hovertool is much better than plotly , at least they put all hover relative things in one place with examples , easy to found what you want, simply add mode='vline' would work

HoverTool(
    tooltips=[
        ( 'date',   '@date{%F}'            ),
        ( 'close',  '$@{adj close}{%0.2f}' ), # use @{ } for field names with spaces
        ( 'volume', '@volume{0.00 a}'      ),
    ],
    formatters={
        'date'      : 'datetime', # use 'datetime' formatter for 'date' field
        'adj close' : 'printf',   # use 'printf' formatter for 'adj close' field
                                  # use default 'numeral' formatter for other fields
    },
    # display a tooltip whenever the cursor is vertically in line with a glyph
    mode='vline
')

plotly document contain many things but didn't group well, find a solution is not easy .

[mogrein]

plotly.py provides "x" and "y" instead of "compare", according to axis you need.

[eromoe]

@mogrein The key requirement is hover a position show **all data** accross **vertical line**
Just look the plotl js version, it show all data(feature) at one x position(by vertical line) .

For example , default behavious don't show all data around this vertical line :

You only can hover show one point (no comparsion to orther features ) , only show green feature below, however there are four different points at here :

[efouquet]

I would also like to be able to use hovermode='compare' as part of the layout specification. Once the plots are actually rendered, clicking on "compare data on hover" in the plotly menu works fine, but there doesn't seem to be any programatic way to have this be the default.

[DradeAW]

Having hovermode="compare" would be really useful in python.
I have multiple subplots with a Scatter plot on each, and when I'm hovering one dot, I'd like it to hover on the other subplots (but the dot doesn't have the same x or y value, it would match by the index in the list).

I don't think it's doable without the "compare" argument.