Visualization

Visualization Skill

Technology Stack

• pyecharts: Python wrapper for Apache ECharts
• Apache ECharts: JavaScript charting library
• Output: Self-contained HTML with embedded JS

Chart Types Reference

Bar Charts

from pyecharts.charts import Bar
from pyecharts import options as opts

chart = Bar()
chart.add_xaxis(labels)
chart.add_yaxis("Series Name", values)
chart.set_global_opts(
    title_opts=opts.TitleOpts(title="Chart Title"),
    tooltip_opts=opts.TooltipOpts(trigger="axis"),
    xaxis_opts=opts.AxisOpts(axislabel_opts=opts.LabelOpts(rotate=45)),
)

Line Charts

from pyecharts.charts import Line

chart = Line()
chart.add_xaxis(dates)
chart.add_yaxis("Actual", values, is_smooth=True)
chart.add_yaxis("7-Day MA", moving_avg_7, is_smooth=True, linestyle_opts=opts.LineStyleOpts(type_="dashed"))

Pie Charts

from pyecharts.charts import Pie

chart = Pie()
chart.add("", list(zip(labels, values)))
chart.set_global_opts(legend_opts=opts.LegendOpts(orient="vertical", pos_left="left"))

Heatmaps

from pyecharts.charts import HeatMap

chart = HeatMap()
chart.add_xaxis(x_labels)
chart.add_yaxis("", y_labels, value=[[x, y, val], ...])
chart.set_global_opts(
    visualmap_opts=opts.VisualMapOpts(min_=0, max_=max_val),
)

Scatter Plots (for anomalies)

from pyecharts.charts import Scatter

chart = Scatter()
chart.add_xaxis(dates)
chart.add_yaxis("Cost", costs, symbol_size=10)
# Add anomaly markers with different color/size

Critical: Browser Compatibility

Always convert to lists for JavaScript:

# CORRECT
chart.add_xaxis(df['column'].tolist())
chart.add_yaxis("Label", df['values'].tolist())

# WRONG - causes rendering issues
chart.add_xaxis(df['column'].values)  # numpy array
chart.add_xaxis(df['column'])  # pandas Series

Theme Options

Available themes in pyecharts:

• macarons (default) - Colorful, professional
• shine - Bright colors
• roma - Muted, elegant
• vintage - Retro feel
• dark - Dark background
• light - Light, minimal

Usage:

from pyecharts.globals import ThemeType
chart = Bar(init_opts=opts.InitOpts(theme=ThemeType.MACARONS))

HTML Report Structure

def generate_html_report(self, output_path: str, top_n: int = 10) -> str:
    # Create all charts
    charts = [
        self.create_cost_by_service_chart(top_n),
        self.create_cost_by_account_chart(),
        # ... more charts
    ]

    # Combine into page
    page = Page(layout=Page.SimplePageLayout)
    for chart in charts:
        page.add(chart)

    # Render to file
    page.render(output_path)
    return output_path

Formatting Numbers

# Currency formatting in tooltips
tooltip_opts=opts.TooltipOpts(
    trigger="axis",
    formatter="{b}: ${c:,.2f}"
)

# Axis label formatting
yaxis_opts=opts.AxisOpts(
    axislabel_opts=opts.LabelOpts(formatter="${value:,.0f}")
)

Common Issues & Solutions

Empty Charts

1. Check browser console for JS errors
2. Verify .tolist() on all data
3. Hard refresh (Ctrl+Shift+R)
4. Check data exists in HTML source

Chart Too Small

init_opts=opts.InitOpts(width="100%", height="400px")

Labels Overlapping

xaxis_opts=opts.AxisOpts(
    axislabel_opts=opts.LabelOpts(rotate=45, interval=0)
)

Legend Too Long

legend_opts=opts.LegendOpts(
    type_="scroll",
    orient="horizontal",
    pos_bottom="0%"
)

Testing Visualizations

# Test chart creation
uv run pytest tests/test_visualizer.py -v

# Regenerate example report
uv run pytest tests/test_examples.py -v -s

# View in browser
open examples/example_report.html