feat(matplotlib): implement streamgraph-basic (#5697)

## Implementation: `streamgraph-basic` - python/matplotlib

Implements the **python/matplotlib** version of `streamgraph-basic`.

**File:** `plots/streamgraph-basic/implementations/python/matplotlib.py`

**Parent Issue:** #856

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/25355850299)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Markus Neusinger <2921697+MarkusNeusinger@users.noreply.github.com>

Author: github-actions[bot]

plots/streamgraph-basic/implementations/python/matplotlib.py

@@ -1,17 +1,26 @@
-""" pyplots.ai
+""" anyplot.ai
 streamgraph-basic: Basic Stream Graph
-Library: matplotlib 3.10.8 | Python 3.13.11
-Quality: 92/100 | Created: 2025-12-23
+Library: matplotlib 3.10.9 | Python 3.13.13
+Quality: 88/100 | Updated: 2026-05-05
 """
 
+import os
+
 import matplotlib.pyplot as plt
 import numpy as np
+from scipy.interpolate import make_interp_spline
+
+
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+ELEVATED_BG = "#FFFDF6" if THEME == "light" else "#242420"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
+INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
 
+OKABE_ITO = ["#009E73", "#D55E00", "#0072B2", "#CC79A7", "#E69F00", "#56B4E9"]
 
-# Data - Monthly streaming hours by music genre over two years
 np.random.seed(42)
 
-# 24 months of data
 months = np.arange(24)
 month_labels = [
     "Jan'23",
@@ -40,68 +49,49 @@
     "Dec'24",
 ]
 
-# Generate realistic genre streaming data with trends
-# Pop - consistently high, slight growth
+# Monthly streaming hours by music genre — diverse trend patterns
 pop = 50 + 10 * np.sin(months / 6) + np.random.randn(24) * 3 + months * 0.3
-
-# Rock - stable with seasonal variation
 rock = 35 + 8 * np.cos(months / 4) + np.random.randn(24) * 2
-
-# Hip-Hop - growing trend
 hiphop = 25 + months * 0.8 + 5 * np.sin(months / 3) + np.random.randn(24) * 3
-
-# Electronic - summer peaks
 electronic = 20 + 15 * np.sin((months - 3) / 6 * np.pi) + np.random.randn(24) * 2
-
-# Jazz - steady, slight decline
 jazz = 18 - months * 0.15 + 4 * np.cos(months / 5) + np.random.randn(24) * 1.5
+classical = 15 + 8 * np.cos(months / 6 * np.pi) + np.random.randn(24) * 1.5
 
-# Classical - winter peaks
-classical = 15 + 8 * np.cos((months) / 6 * np.pi) + np.random.randn(24) * 1.5
-
-# Ensure all values are positive
-pop = np.maximum(pop, 5)
-rock = np.maximum(rock, 5)
-hiphop = np.maximum(hiphop, 5)
-electronic = np.maximum(electronic, 5)
-jazz = np.maximum(jazz, 5)
-classical = np.maximum(classical, 5)
+data_raw = [pop, rock, hiphop, electronic, jazz, classical]
+for arr in data_raw:
+    np.maximum(arr, 5, out=arr)
 
-# Stack the data
-data = np.vstack([pop, rock, hiphop, electronic, jazz, classical])
 categories = ["Pop", "Rock", "Hip-Hop", "Electronic", "Jazz", "Classical"]
 
-# Colors - starting with Python Blue/Yellow, then colorblind-safe palette
-colors = ["#306998", "#FFD43B", "#E07A5F", "#81B29A", "#F2CC8F", "#3D405B"]
-
-# Create plot (4800x2700 px)
-fig, ax = plt.subplots(figsize=(16, 9))
+# Cubic spline interpolation → smooth, flowing curves
+months_fine = np.linspace(0, 23, 300)
+data_smooth = np.array([np.maximum(make_interp_spline(months, series, k=3)(months_fine), 1.0) for series in data_raw])
 
-# Create streamgraph with symmetric baseline (wiggle for stream-like appearance)
-ax.stackplot(months, data, labels=categories, colors=colors, baseline="wiggle", alpha=0.85)
+fig, ax = plt.subplots(figsize=(16, 9), facecolor=PAGE_BG)
+ax.set_facecolor(PAGE_BG)
 
-# Styling
-ax.set_xlabel("Month", fontsize=20)
-ax.set_title("streamgraph-basic · matplotlib · pyplots.ai", fontsize=24)
+ax.stackplot(months_fine, data_smooth, labels=categories, colors=OKABE_ITO, baseline="wiggle", alpha=0.85)
 
-# X-axis labels
-ax.set_xticks(months[::3])
-ax.set_xticklabels([month_labels[i] for i in range(0, 24, 3)], fontsize=16)
-ax.tick_params(axis="y", labelsize=16)
+ax.set_xlabel("Month (Jan 2023 – Dec 2024)", fontsize=20, color=INK)
+ax.set_title("streamgraph-basic · matplotlib · anyplot.ai", fontsize=24, color=INK, fontweight="medium")
 
-# Remove y-axis ticks for cleaner stream appearance (values are relative)
+tick_positions = list(range(0, 24, 3))
+ax.set_xticks(tick_positions)
+ax.set_xticklabels([month_labels[i] for i in tick_positions], fontsize=16)
+ax.tick_params(axis="x", colors=INK_SOFT, labelcolor=INK_SOFT)
 ax.set_yticks([])
 
-# Add legend
-ax.legend(loc="upper left", fontsize=16, framealpha=0.9)
-
-# Subtle styling - remove top and right spines
 ax.spines["top"].set_visible(False)
 ax.spines["right"].set_visible(False)
 ax.spines["left"].set_visible(False)
+ax.spines["bottom"].set_color(INK_SOFT)
+
+ax.set_xlim(months_fine[0], months_fine[-1])
 
-# Set x limits to remove padding
-ax.set_xlim(0, 23)
+leg = ax.legend(loc="upper left", fontsize=16, framealpha=0.9)
+leg.get_frame().set_facecolor(ELEVATED_BG)
+leg.get_frame().set_edgecolor(INK_SOFT)
+plt.setp(leg.get_texts(), color=INK_SOFT)
 
 plt.tight_layout()
-plt.savefig("plot.png", dpi=300, bbox_inches="tight")
+plt.savefig(f"plot-{THEME}.png", dpi=300, bbox_inches="tight", facecolor=PAGE_BG)