feat(pygal): implement range-interval

plots/range-interval/implementations/pygal.py

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+""" pyplots.ai
+range-interval: Range Interval Chart
+Library: pygal 3.1.0 | Python 3.13.11
+Quality: 91/100 | Created: 2026-01-09
+"""
+
+import pygal
+from pygal.style import Style
+
+
+# Data: Monthly temperature ranges (daily high/low averages)
+months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
+temp_min = [-2, 0, 4, 8, 13, 17, 19, 18, 14, 9, 4, 0]  # Average daily lows (°C)
+temp_max = [6, 8, 12, 16, 21, 25, 28, 27, 22, 16, 10, 7]  # Average daily highs (°C)
+
+# Calculate the range (difference) for the visible portion
+temp_range = [high - low for low, high in zip(temp_min, temp_max, strict=True)]
+
+# Custom style for large canvas
+# The base (transparent) color needs to be invisible
+custom_style = Style(
+    background="white",
+    plot_background="white",
+    foreground="#333333",
+    foreground_strong="#333333",
+    foreground_subtle="#666666",
+    colors=("rgba(0, 0, 0, 0)", "#306998"),  # First series invisible, second visible
+    title_font_size=56,
+    label_font_size=36,
+    major_label_font_size=32,
+    legend_font_size=36,
+    value_font_size=28,
+    tooltip_font_size=24,
+    opacity=1.0,
+    opacity_hover=1.0,
+)
+
+# Create stacked bar chart - first bar is invisible base, second is visible range
+chart = pygal.StackedBar(
+    width=4800,
+    height=2700,
+    style=custom_style,
+    title="range-interval · pygal · pyplots.ai",
+    x_title="Month",
+    y_title="Temperature (°C)",
+    show_legend=True,
+    legend_at_bottom=True,
+    legend_at_bottom_columns=2,
+    show_y_guides=True,
+    show_x_guides=False,
+    print_values=False,
+    spacing=40,
+    margin=80,
+    margin_bottom=150,
+    margin_left=150,
+    truncate_legend=-1,
+)
+
+# Set x-axis labels
+chart.x_labels = months
+
+# Add invisible base (from 0 to min_value) - hidden from legend
+chart.add("", temp_min, show_dots=False)
+
+# Add visible range bars (from min to max)
+chart.add("Temperature Range (°C)", temp_range)
+
+# Render to PNG and HTML
+chart.render_to_png("plot.png")
+chart.render_to_file("plot.html")

plots/range-interval/metadata/pygal.yaml

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+library: pygal
+specification_id: range-interval
+created: '2026-01-09T23:49:05Z'
+updated: '2026-01-09T23:53:46Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20868894824
+issue: 3577
+python_version: 3.13.11
+library_version: 3.1.0
+preview_url: https://storage.googleapis.com/pyplots-images/plots/range-interval/pygal/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/range-interval/pygal/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/range-interval/pygal/plot.html
+quality_score: 91
+review:
+  strengths:
+  - Clever implementation using stacked bar with invisible base to create floating
+    range bars
+  - Clean, professional appearance with good color choice
+  - Realistic temperature data showing clear seasonal variation
+  - Proper title format and axis labels with units
+  - Good canvas utilization and layout balance
+  weaknesses:
+  - Grid & legend could be improved - the invisible series technique leaves legend
+    slightly awkward
+  - Missing optional endpoint markers at min/max points as suggested in spec notes
+  - Could leverage more pygal-specific interactive features
+  image_description: 'The plot displays a range interval chart showing monthly temperature
+    ranges across 12 months (Jan-Dec). Each month is represented by a blue (#306998)
+    floating bar that spans from the minimum to maximum temperature for that month.
+    The y-axis shows "Temperature (°C)" ranging from -2 to 28, and the x-axis shows
+    "Month" with abbreviated month labels. The title correctly reads "range-interval
+    · pygal · pyplots.ai" at the top. A legend at the bottom displays "Temperature
+    Range (°C)". Horizontal grid lines are visible at 2-degree intervals. The bars
+    effectively show the seasonal pattern with narrow ranges in winter months (Jan:
+    -2 to 6°C, Feb: 0 to 8°C) and wider, higher ranges in summer (Jul: 19 to 28°C).
+    The overall layout is clean with good use of whitespace.'
+  criteria_checklist:
+    visual_quality:
+      score: 36
+      max: 40
+      items:
+      - id: VQ-01
+        name: Text Legibility
+        score: 9
+        max: 10
+        passed: true
+        comment: Title and axis labels are clearly readable. Font sizes are appropriate
+          for the canvas size. Tick labels slightly small but still legible.
+      - id: VQ-02
+        name: No Overlap
+        score: 8
+        max: 8
+        passed: true
+        comment: No overlapping text elements. Month labels are well-spaced.
+      - id: VQ-03
+        name: Element Visibility
+        score: 7
+        max: 8
+        passed: true
+        comment: Bars are clearly visible with good sizing. Could benefit from slightly
+          more contrast or edge highlighting.
+      - id: VQ-04
+        name: Color Accessibility
+        score: 5
+        max: 5
+        passed: true
+        comment: Single blue color scheme is colorblind-safe. Good contrast against
+          white background.
+      - id: VQ-05
+        name: Layout Balance
+        score: 5
+        max: 5
+        passed: true
+        comment: Plot fills canvas well with balanced margins. Good use of space.
+      - id: VQ-06
+        name: Axis Labels
+        score: 2
+        max: 2
+        passed: true
+        comment: 'Descriptive labels with units: Temperature (°C) and Month.'
+      - id: VQ-07
+        name: Grid & Legend
+        score: 0
+        max: 2
+        passed: false
+        comment: Legend placement at bottom is acceptable but the invisible series
+          creates a gap. Grid is subtle but works.
+    spec_compliance:
+      score: 23
+      max: 25
+      items:
+      - id: SC-01
+        name: Plot Type
+        score: 8
+        max: 8
+        passed: true
+        comment: Correct range interval chart implementation using stacked bar technique.
+      - id: SC-02
+        name: Data Mapping
+        score: 5
+        max: 5
+        passed: true
+        comment: Categories on x-axis, range values on y-axis as specified.
+      - id: SC-03
+        name: Required Features
+        score: 4
+        max: 5
+        passed: true
+        comment: Shows min-max ranges effectively. Missing optional endpoint markers
+          mentioned in spec notes.
+      - id: SC-04
+        name: Data Range
+        score: 3
+        max: 3
+        passed: true
+        comment: Y-axis range appropriately shows all data from -2 to 28.
+      - id: SC-05
+        name: Legend Accuracy
+        score: 2
+        max: 2
+        passed: true
+        comment: Legend correctly identifies the temperature range.
+      - id: SC-06
+        name: Title Format
+        score: 1
+        max: 2
+        passed: true
+        comment: Title uses correct format but uses regular dot which displays correctly.
+    data_quality:
+      score: 19
+      max: 20
+      items:
+      - id: DQ-01
+        name: Feature Coverage
+        score: 7
+        max: 8
+        passed: true
+        comment: Shows variation in range sizes across seasons. Winter months have
+          narrow ranges, summer months have wider ranges. Good seasonal pattern.
+      - id: DQ-02
+        name: Realistic Context
+        score: 7
+        max: 7
+        passed: true
+        comment: Monthly temperature ranges for a temperate climate location. Realistic
+          and neutral scenario.
+      - id: DQ-03
+        name: Appropriate Scale
+        score: 5
+        max: 5
+        passed: true
+        comment: Temperature values are realistic for a temperate European climate.
+    code_quality:
+      score: 10
+      max: 10
+      items:
+      - id: CQ-01
+        name: KISS Structure
+        score: 3
+        max: 3
+        passed: true
+        comment: 'Simple script structure: imports, data, chart config, save. No functions
+          or classes.'
+      - id: CQ-02
+        name: Reproducibility
+        score: 3
+        max: 3
+        passed: true
+        comment: Data is deterministic (hardcoded values), no randomness.
+      - id: CQ-03
+        name: Clean Imports
+        score: 2
+        max: 2
+        passed: true
+        comment: Only pygal and Style imported, both are used.
+      - id: CQ-04
+        name: No Deprecated API
+        score: 1
+        max: 1
+        passed: true
+        comment: Uses current pygal API.
+      - id: CQ-05
+        name: Output Correct
+        score: 1
+        max: 1
+        passed: true
+        comment: Saves as plot.png and plot.html.
+    library_features:
+      score: 3
+      max: 5
+      items:
+      - id: LF-01
+        name: Distinctive Features
+        score: 3
+        max: 5
+        passed: true
+        comment: Uses pygal's StackedBar with custom Style effectively. The invisible
+          base bar technique is clever. Could use more pygal-specific features like
+          tooltips or animation.
+  verdict: APPROVED
+impl_tags:
+  dependencies: []
+  techniques:
+  - html-export
+  patterns: []
+  dataprep: []
+  styling: []