plotly / plotly/plotly.py

Default bar width on date axes should be smarter

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feature P3
Dominant language
Python
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Description

This is likely a similar issue to https://github.com/plotly/plotly.js/issues/6199

Plotly version: 6.2.0

Minimal Example
import plotly.graph_objects as go
import pandas as pd
import datetime

data = [
    {"date": datetime.date(2025,7,20), "net_sales": 23.34, "gross_sales": 32.98},
    {"date": datetime.date(2025,7,21), "net_sales": 45.21, "gross_sales": 68.12},
    {"date": datetime.date(2025,7,22), "net_sales": 12.98, "gross_sales": 34.54},
    {"date": datetime.date(2025,7,23), "net_sales": 41.32, "gross_sales": 45.32},
]

df = pd.DataFrame.from_records(data)

def make_figure(df, width=None):
    fig = go.Figure()
    fig.add_trace(go.Bar(
        x=df['date'],
        y=df['net_sales'],
        xperiod=24*60*60*1000,
        xperiod0=df['date'].min(),
        xperiodalignment="middle"
    ))
    fig.add_trace(go.Bar(
        x=df['date'],
        y=df['gross_sales'],
        xperiod=24*60*60*1000,
        xperiod0=df['date'].min(),
        xperiodalignment="middle"
    ))
    fig.update_layout(
        xaxis={
            'ticklabelmode': 'period',
            'tickmode': 'auto',
            'dtick': 24*60*60*1000,
            'range': (df['date'].min(), df['date'].max() + datetime.timedelta(days=1))
        })
    fig.show(renderer="browser")

make_figure(df)
make_figure(df[0:1])

When plotting a bar chart of aggregated timeseries data, strange behaviour happens when there's only 1 data point or group. When there are multiple bars each bar is displayed as one would expect (first screenshot below), but when there's only a single data point the bar is invisible, and specifically the bar width is set to 1ms or 0.5px (second screenshot).

Image Image

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the minimal Python example in the issue and compare the behavior with plotly.js issue #6199. Done means a single date point renders a visible bar with a sensible default width while multi-point bars retain their current behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
data-visualization
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
38/100

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