feat(pygal): implement ohlc-bar

plots/ohlc-bar/implementations/pygal.py

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+""" pyplots.ai
+ohlc-bar: OHLC Bar Chart
+Library: pygal 3.1.0 | Python 3.13.11
+Quality: 90/100 | Created: 2026-01-08
+"""
+
+import numpy as np
+import pandas as pd
+import pygal
+from pygal.style import Style
+
+
+# Data - Generate realistic stock price data
+np.random.seed(42)
+n_days = 40
+
+# Starting price and generate daily returns
+start_price = 150.0
+daily_returns = np.random.normal(0.001, 0.02, n_days)
+
+# Generate OHLC data
+dates = pd.date_range("2024-06-01", periods=n_days, freq="B")  # Business days
+closes = start_price * np.cumprod(1 + daily_returns)
+opens = np.roll(closes, 1)
+opens[0] = start_price
+
+# Generate highs and lows based on volatility
+daily_volatility = np.abs(np.random.normal(0.01, 0.005, n_days))
+highs = np.maximum(opens, closes) * (1 + daily_volatility)
+lows = np.minimum(opens, closes) * (1 - daily_volatility)
+
+# Custom style for 4800x2700 px canvas
+# Use green for up bars, red for down bars
+up_color = "#27AE60"
+down_color = "#E74C3C"
+
+custom_style = Style(
+    background="white",
+    plot_background="white",
+    foreground="#333333",
+    foreground_strong="#333333",
+    foreground_subtle="#999999",
+    guide_stroke_color="#CCCCCC",
+    opacity=".95",
+    opacity_hover=".85",
+    colors=(up_color, down_color),
+    title_font_size=60,
+    label_font_size=32,
+    major_label_font_size=28,
+    legend_font_size=32,
+    value_font_size=28,
+    tooltip_font_size=24,
+    stroke_width=6,
+)
+
+# Create date labels for x-axis (every 5th date for clarity)
+date_labels = {i: dates[i].strftime("%b %d") for i in range(0, n_days, 5)}
+
+# Create XY chart with legend near plot
+chart = pygal.XY(
+    width=4800,
+    height=2700,
+    style=custom_style,
+    title="ohlc-bar · pygal · pyplots.ai",
+    x_title="Date (Jun-Aug 2024)",
+    y_title="Price ($)",
+    show_legend=True,
+    legend_at_bottom=True,
+    legend_at_bottom_columns=2,
+    legend_box_size=24,
+    show_x_guides=False,
+    show_y_guides=True,
+    truncate_label=-1,
+    truncate_legend=-1,
+    stroke=True,
+    show_dots=False,
+    x_labels=list(date_labels.values()),
+    x_labels_major_every=1,
+)
+
+# Tick width for open/close marks (slightly wider for visibility)
+tick_width = 0.4
+
+# Build OHLC bar segments - each bar needs:
+# 1. Vertical line from low to high
+# 2. Open tick (left horizontal)
+# 3. Close tick (right horizontal)
+
+# Separate up and down bars into different series
+up_bars = []  # Each bar as list of points with None separators
+down_bars = []
+
+for i in range(n_days):
+    x = float(i)
+    o, h, lo, c = opens[i], highs[i], lows[i], closes[i]
+
+    # Each OHLC bar: vertical line + open tick + close tick
+    bar_points = [
+        # Vertical line (low to high)
+        (x, lo),
+        (x, h),
+        # Break
+        (None, None),
+        # Open tick (left horizontal)
+        (x - tick_width, o),
+        (x, o),
+        # Break
+        (None, None),
+        # Close tick (right horizontal)
+        (x, c),
+        (x + tick_width, c),
+        # Break for next bar
+        (None, None),
+    ]
+
+    if c >= o:  # Up bar (bullish)
+        up_bars.extend(bar_points)
+    else:  # Down bar (bearish)
+        down_bars.extend(bar_points)
+
+# Add series with descriptive legend labels
+chart.add("Bullish (Close ≥ Open)", up_bars)
+chart.add("Bearish (Close < Open)", down_bars)
+
+# Save outputs
+chart.render_to_png("plot.png")
+chart.render_to_file("plot.html")

plots/ohlc-bar/metadata/pygal.yaml

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+library: pygal
+specification_id: ohlc-bar
+created: '2026-01-08T16:12:54Z'
+updated: '2026-01-08T16:24:48Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20823200220
+issue: 3293
+python_version: 3.13.11
+library_version: 3.1.0
+preview_url: https://storage.googleapis.com/pyplots-images/plots/ohlc-bar/pygal/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/ohlc-bar/pygal/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/ohlc-bar/pygal/plot.html
+quality_score: 90
+review:
+  strengths:
+  - Correct OHLC bar representation using pygal XY chart with creative line segment
+    approach
+  - Good color differentiation between bullish (green) and bearish (red) bars
+  - Clean code structure following KISS principles
+  - Appropriate font sizes for the 4800x2700 canvas
+  - Realistic stock price data generation with proper OHLC relationships
+  weaknesses:
+  - X-axis shows numeric indices instead of actual date labels despite dates being
+    generated
+  - Missing horizontal grid lines which spec mentions for reading price levels
+  - Legend labels in output differ from code comments (Up/Down vs Bullish/Bearish)
+  image_description: 'The plot displays an OHLC (Open-High-Low-Close) bar chart with
+    40 trading days of stock price data on a white background. Green bars indicate
+    bullish days (close ≥ open) and red bars indicate bearish days (close < open).
+    Each OHLC bar correctly shows: a vertical line for the high-low range, a left
+    horizontal tick for the opening price, and a right horizontal tick for the closing
+    price. The chart shows a general downtrend from approximately $150 to $130 over
+    the period. The title "ohlc-bar · pygal · pyplots.ai" appears at top center. Y-axis
+    is labeled "Price ($)" ranging from ~130 to ~166. X-axis is labeled "Trading Day"
+    with numeric indices 0-36. A legend at the bottom shows "Up (Close ≥ Open)" in
+    green and "Down (Close < Open)" in red. Light gray dashed vertical grid lines
+    are visible.'
+  criteria_checklist:
+    visual_quality:
+      score: 35
+      max: 40
+      items:
+      - id: VQ-01
+        name: Text Legibility
+        score: 10
+        max: 10
+        passed: true
+        comment: Title, axis labels, and tick labels are all clearly readable at the
+          canvas size
+      - id: VQ-02
+        name: No Overlap
+        score: 8
+        max: 8
+        passed: true
+        comment: No overlapping text elements; bars are well-spaced
+      - id: VQ-03
+        name: Element Visibility
+        score: 7
+        max: 8
+        passed: true
+        comment: OHLC bars are visible and distinguishable, though some bars overlap
+          slightly due to data density
+      - id: VQ-04
+        name: Color Accessibility
+        score: 5
+        max: 5
+        passed: true
+        comment: Green/red color scheme is standard for financial charts and has good
+          contrast on white background
+      - id: VQ-05
+        name: Layout Balance
+        score: 3
+        max: 5
+        passed: true
+        comment: Good use of canvas space, but x-axis shows numeric indices instead
+          of date labels which reduces context
+      - id: VQ-06
+        name: Axis Labels
+        score: 2
+        max: 2
+        passed: true
+        comment: Y-axis has Price ($) with units, X-axis has Trading Day which is
+          descriptive
+      - id: VQ-07
+        name: Grid & Legend
+        score: 0
+        max: 2
+        passed: false
+        comment: Only vertical grid lines visible; missing horizontal guides for price
+          levels; legend is well-placed but uses different label format than code
+    spec_compliance:
+      score: 23
+      max: 25
+      items:
+      - id: SC-01
+        name: Plot Type
+        score: 8
+        max: 8
+        passed: true
+        comment: Correct OHLC bar chart with vertical lines and horizontal ticks
+      - id: SC-02
+        name: Data Mapping
+        score: 5
+        max: 5
+        passed: true
+        comment: Date on X-axis, price on Y-axis, OHLC values correctly mapped
+      - id: SC-03
+        name: Required Features
+        score: 4
+        max: 5
+        passed: true
+        comment: Has open/close ticks, high-low lines, color coding; but spec mentions
+          horizontal grid lines for reading price levels which are missing
+      - id: SC-04
+        name: Data Range
+        score: 3
+        max: 3
+        passed: true
+        comment: All data points visible within axes range
+      - id: SC-05
+        name: Legend Accuracy
+        score: 1
+        max: 2
+        passed: true
+        comment: Legend labels differ from code (shows Up/Down not Bullish/Bearish)
+      - id: SC-06
+        name: Title Format
+        score: 2
+        max: 2
+        passed: true
+        comment: 'Correct format: ohlc-bar · pygal · pyplots.ai'
+    data_quality:
+      score: 19
+      max: 20
+      items:
+      - id: DQ-01
+        name: Feature Coverage
+        score: 8
+        max: 8
+        passed: true
+        comment: Shows both bullish and bearish bars, various price ranges, realistic
+          price movements
+      - id: DQ-02
+        name: Realistic Context
+        score: 6
+        max: 7
+        passed: true
+        comment: Plausible stock price scenario with business days, but no specific
+          stock context
+      - id: DQ-03
+        name: Appropriate Scale
+        score: 5
+        max: 5
+        passed: true
+        comment: Price values ($130-$166) are realistic for stock prices
+    code_quality:
+      score: 10
+      max: 10
+      items:
+      - id: CQ-01
+        name: KISS Structure
+        score: 3
+        max: 3
+        passed: true
+        comment: Clean imports → data → plot → save structure, no unnecessary functions/classes
+      - id: CQ-02
+        name: Reproducibility
+        score: 3
+        max: 3
+        passed: true
+        comment: Uses np.random.seed(42) for reproducibility
+      - id: CQ-03
+        name: Clean Imports
+        score: 2
+        max: 2
+        passed: true
+        comment: All imports are used (numpy, pandas, pygal, Style)
+      - 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 Style customization and XY chart with line segments to
+          create OHLC bars; creative use of None separators for discontinuous lines
+  verdict: APPROVED
+impl_tags:
+  dependencies: []
+  techniques:
+  - html-export
+  patterns:
+  - data-generation
+  - iteration-over-groups
+  dataprep:
+  - time-series
+  styling: []