feat(plotnine): implement indicator-sma

[github-actions]

Implementation: indicator-sma - plotnine

Implements the plotnine version of indicator-sma.

File: plots/indicator-sma/implementations/plotnine.py

Parent Issue: #3651

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🤖 impl-generate workflow

[claude]

AI Review - Attempt 1/3

Image Description

The plot displays a Simple Moving Average (SMA) indicator chart with a dark blue price line showing daily stock prices over approximately one year (Jan 2024 - Feb 2025). Three SMA overlay lines are visible: a yellow SMA 20 (short-term), a red SMA 50 (medium-term), and a green SMA 200 (long-term). The price fluctuates between roughly $130-$170, showing a downward trend from Jan-Aug 2024 followed by an upward trend from Oct 2024 onwards. The legend is positioned in the upper left corner. The title follows the correct format "indicator-sma · plotnine · pyplots.ai" in bold at the top. X-axis shows dates with rotated labels, Y-axis shows "Price ($)". Grid lines are subtle on the y-axis only.

Quality Score: 91/100

Criteria Checklist

Visual Quality (36/40 pts)

• VQ-01: Text Legibility (10/10) - Title is bold and large, axis labels are clearly readable, tick labels appropriately sized
• VQ-02: No Overlap (8/8) - No overlapping text elements, date labels are rotated to avoid overlap
• VQ-03: Element Visibility (7/8) - Line widths are good (1.5), all four series are clearly distinguishable, alpha of 0.9 works well
• VQ-04: Color Accessibility (5/5) - Colors are distinct: blue, yellow, red, green - colorblind-friendly choices
• VQ-05: Layout Balance (4/5) - Good use of canvas space, legend well positioned in upper-left, minimal wasted space
• VQ-06: Axis Labels (2/2) - Y-axis has units "Price ($)", X-axis labeled "Date"
• VQ-07: Grid & Legend (0/2) - Grid is very subtle (good), but legend lacks a background/frame making it slightly hard to read against data

Spec Compliance (25/25 pts)

• SC-01: Plot Type (8/8) - Correct line chart with price and three SMA overlays
• SC-02: Data Mapping (5/5) - Date on X-axis, price values on Y-axis, correctly mapped
• SC-03: Required Features (5/5) - All required features present: price line, 20/50/200-day SMAs, legend with periods
• SC-04: Data Range (3/3) - All data visible, axes accommodate full range
• SC-05: Legend Accuracy (2/2) - Legend correctly shows "Price", "SMA 20", "SMA 50", "SMA 200"
• SC-06: Title Format (2/2) - Correct format "indicator-sma · plotnine · pyplots.ai"

Data Quality (18/20 pts)

• DQ-01: Feature Coverage (7/8) - Shows uptrend and downtrend, SMAs crossing, different lag behavior of each SMA period. Could show a clearer golden/death cross signal
• DQ-02: Realistic Context (7/7) - Realistic stock price scenario with plausible volatility and price range (~$130-$170)
• DQ-03: Appropriate Scale (4/5) - 300 business days is appropriate; price range is realistic but somewhat narrow

Code Quality (9/10 pts)

• CQ-01: KISS Structure (3/3) - Clean linear structure: imports → data → plot → save
• CQ-02: Reproducibility (3/3) - np.random.seed(42) is set
• CQ-03: Clean Imports (2/2) - All imports are used
• CQ-04: No Deprecated API (1/1) - Current API usage
• CQ-05: Output Correct (0/1) - Saves as plot.png correctly

Library Features (3/5 pts)

• LF-01: Uses distinctive library features (3/5) - Uses plotnine's ggplot grammar, theme_minimal, scale_color_manual, and proper long-format data transformation with pd.melt which is idiomatic for plotnine

Strengths

• Excellent use of plotnine's grammar of graphics with proper long-format data transformation
• Clean color scheme that distinguishes all four series effectively
• Proper title format following the spec-id · library · pyplots.ai convention
• Good handling of date axis with appropriate rotation to prevent overlap
• Realistic synthetic stock price data with visible trend behavior
• All three SMA periods (20, 50, 200) are correctly calculated and displayed

Weaknesses

• Legend could benefit from a background/box for better readability against data
• The SMA 200 line only appears in the final third of the chart due to the 200-day window requirement - this is technically correct but reduces visual impact

Verdict: APPROVED