feat(pygal): implement indicator-ema (#7350)

## Implementation: `indicator-ema` - python/pygal

Implements the **python/pygal** version of `indicator-ema`.

**File:** `plots/indicator-ema/implementations/python/pygal.py`

**Parent Issue:** #3652

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/26076885400)*

---------

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/indicator-ema/implementations/python/pygal.py

@@ -1,40 +1,57 @@
-""" pyplots.ai
+""" anyplot.ai
 indicator-ema: Exponential Moving Average (EMA) Indicator Chart
-Library: pygal 3.1.0 | Python 3.13.11
-Quality: 91/100 | Created: 2026-01-11
+Library: pygal 3.1.0 | Python 3.13.13
+Quality: 86/100 | Updated: 2026-05-19
 """
 
+import os
+import sys
+
+
+# Prevent the local pygal.py from shadowing the installed pygal package
+_here = os.path.dirname(os.path.abspath(__file__))
+sys.path = [p for p in sys.path if os.path.abspath(p or ".") != _here]
+
 import numpy as np
 import pandas as pd
 import pygal
 from pygal.style import Style
 
 
-# Data - Generate synthetic stock price data with EMA indicators
-np.random.seed(42)
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
+INK_MUTED = "#6B6A63" if THEME == "light" else "#A8A79F"
 
-# Create 120 trading days
-dates = pd.date_range(start="2024-01-02", periods=120, freq="B")  # Business days
+OKABE_ITO = ("#009E73", "#D55E00", "#0072B2", "#CC79A7", "#E69F00", "#56B4E9", "#F0E442")
 
-# Generate realistic stock price movement (random walk with drift)
+# Data
+np.random.seed(42)
+dates = pd.date_range(start="2024-01-02", periods=120, freq="B")
 initial_price = 150.0
-returns = np.random.normal(0.0008, 0.018, 120)  # Daily returns with slight upward drift
+returns = np.random.normal(0.0008, 0.018, 120)
 prices = initial_price * np.cumprod(1 + returns)
 
-
-# Calculate EMAs (exponentially weighted moving average)
 close = prices
 ema_12 = pd.Series(close).ewm(span=12, adjust=False).mean().values
 ema_26 = pd.Series(close).ewm(span=26, adjust=False).mean().values
 
-# Custom style for large canvas
+# Detect EMA crossover points
+crossover_vals = [None] * len(close)
+for i in range(1, len(ema_12)):
+    prev_diff = ema_12[i - 1] - ema_26[i - 1]
+    curr_diff = ema_12[i] - ema_26[i]
+    if prev_diff * curr_diff < 0:
+        crossover_vals[i] = float(close[i])
+
+# Style
 custom_style = Style(
-    background="white",
-    plot_background="white",
-    foreground="#333333",
-    foreground_strong="#333333",
-    foreground_subtle="#666666",
-    colors=("#306998", "#FFD43B", "#E74C3C"),  # Price in blue, EMA12 in yellow, EMA26 in red
+    background=PAGE_BG,
+    plot_background=PAGE_BG,
+    foreground=INK,
+    foreground_strong=INK,
+    foreground_subtle=INK_MUTED,
+    colors=OKABE_ITO,
     title_font_size=72,
     label_font_size=48,
     major_label_font_size=42,
@@ -46,34 +63,35 @@
     opacity_hover=1.0,
 )
 
-# Create line chart
+# Chart
 chart = pygal.Line(
     width=4800,
     height=2700,
     style=custom_style,
-    title="indicator-ema · pygal · pyplots.ai",
+    title="indicator-ema · python · pygal · anyplot.ai",
     x_title="Date",
     y_title="Price ($)",
-    show_dots=False,  # Cleaner line appearance
-    show_x_guides=False,
+    show_dots=False,
+    show_x_guides=True,
     show_y_guides=True,
     stroke_style={"width": 6},
     legend_at_bottom=True,
-    legend_at_bottom_columns=3,
+    legend_at_bottom_columns=4,
     x_label_rotation=45,
     truncate_label=10,
     show_minor_x_labels=False,
+    dots_size=10,
 )
 
-# Format date labels (show every 10th date)
 chart.x_labels = [d.strftime("%Y-%m-%d") for d in dates]
 chart.x_labels_major = [dates[i].strftime("%Y-%m-%d") for i in range(0, len(dates), 20)]
 
-# Add data series - Price line should be most prominent
 chart.add("Close Price", close.tolist(), stroke_style={"width": 8})
 chart.add("EMA 12-day", ema_12.tolist(), stroke_style={"width": 5, "dasharray": "10,5"})
 chart.add("EMA 26-day", ema_26.tolist(), stroke_style={"width": 5, "dasharray": "5,5"})
+chart.add("Crossovers", crossover_vals, show_dots=True, stroke=False)
 
-# Save as PNG and HTML
-chart.render_to_png("plot.png")
-chart.render_to_file("plot.html")
+# Save
+chart.render_to_png(f"plot-{THEME}.png")
+with open(f"plot-{THEME}.html", "wb") as f:
+    f.write(chart.render())