feat(plotnine): implement funnel-basic (#5429)

## Implementation: `funnel-basic` - python/plotnine

Implements the **python/plotnine** version of `funnel-basic`.

**File:** `plots/funnel-basic/implementations/python/plotnine.py`

**Parent Issue:** #789

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:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/24949287748)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/funnel-basic/implementations/python/plotnine.py

@@ -1,65 +1,106 @@
-""" pyplots.ai
+""" anyplot.ai
 funnel-basic: Basic Funnel Chart
-Library: plotnine 0.15.2 | Python 3.13.11
-Quality: 91/100 | Created: 2025-12-23
+Library: plotnine 0.15.3 | Python 3.14.4
+Quality: 87/100 | Updated: 2026-04-26
 """
 
-# Fix import conflict: script named plotnine.py shadows the plotnine package
+# Script filename "plotnine.py" shadows the plotnine package on sys.path.
+# Drop the script's own directory before importing.
+import os
 import sys
 
 
-sys.path = [p for p in sys.path if not p.endswith("implementations")]
+sys.path = [p for p in sys.path if not p.endswith("implementations/python")]
 
 import pandas as pd  # noqa: E402
 from plotnine import (  # noqa: E402
     aes,
     element_blank,
+    element_rect,
     element_text,
-    geom_rect,
+    geom_polygon,
     geom_text,
     ggplot,
     labs,
+    scale_color_identity,
     scale_fill_manual,
+    scale_y_reverse,
     theme,
-    theme_minimal,
+    theme_void,
 )
 
 
-# Data - Sales funnel with 5 stages showing clear progression
-stages = ["Awareness", "Interest", "Consideration", "Intent", "Purchase"]
-values = [1000, 600, 400, 200, 100]
+# Theme tokens
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
 
-df = pd.DataFrame({"stage": stages, "value": values})
+# Okabe-Ito palette — first stage is brand green (#009E73)
+OKABE_ITO = ["#009E73", "#D55E00", "#0072B2", "#CC79A7", "#E69F00"]
+# Light orange (#E69F00) needs dark text for contrast; others use white.
+TEXT_ON_FILL = ["white", "white", "white", "white", INK]
 
-# Calculate funnel geometry - centered bars with widths proportional to values
-max_value = df["value"].max()
-df["width"] = df["value"] / max_value  # Normalize widths (0-1 scale)
-df["y"] = range(len(df), 0, -1)  # Y positions (top to bottom)
-df["xmin"] = -df["width"] / 2
-df["xmax"] = df["width"] / 2
-df["ymin"] = df["y"] - 0.4
-df["ymax"] = df["y"] + 0.4
-
-# Labels with values and percentages
-df["label"] = df.apply(lambda row: f"{row['stage']}\n{row['value']:,} ({row['value'] / max_value * 100:.0f}%)", axis=1)
+# Data — sales funnel example from specification
+stages = ["Awareness", "Interest", "Consideration", "Intent", "Purchase"]
+values = [1000, 600, 400, 200, 100]
+n_stages = len(stages)
+max_value = values[0]
 
-# Stage as ordered categorical for legend order
-df["stage"] = pd.Categorical(df["stage"], categories=stages, ordered=True)
+# Build trapezoid polygon vertices for each stage
+gap = 0.06
+polygons = []
+labels = []
+for i, (stage, value) in enumerate(zip(stages, values, strict=True)):
+    w_top = value / max_value
+    # Flat bottom on the last segment — match its own width.
+    w_bot = (values[i + 1] / max_value) if i + 1 < n_stages else w_top
+    y_top = i + gap / 2
+    y_bot = (i + 1) - gap / 2
+    polygons.extend(
+        [
+            {"stage": stage, "x": -w_top / 2, "y": y_top, "order": 0},
+            {"stage": stage, "x": w_top / 2, "y": y_top, "order": 1},
+            {"stage": stage, "x": w_bot / 2, "y": y_bot, "order": 2},
+            {"stage": stage, "x": -w_bot / 2, "y": y_bot, "order": 3},
+        ]
+    )
+    pct = value / max_value * 100
+    labels.append(
+        {
+            "stage": stage,
+            "x": 0,
+            "y": (y_top + y_bot) / 2,
+            "label": f"{stage}\n{value:,}  ·  {pct:.0f}%",
+            "text_color": TEXT_ON_FILL[i],
+        }
+    )
 
-# Colors - Python Blue to lighter shades for progression
-colors = ["#306998", "#4A7FA8", "#6495B8", "#7EABC8", "#98C1D8"]
+df_poly = pd.DataFrame(polygons)
+df_poly["stage"] = pd.Categorical(df_poly["stage"], categories=stages, ordered=True)
+df_labels = pd.DataFrame(labels)
 
-# Create funnel plot using rectangles
+# Plot
 plot = (
-    ggplot(df, aes(xmin="xmin", xmax="xmax", ymin="ymin", ymax="ymax", fill="stage"))
-    + geom_rect(color="white", size=0.5)
-    + geom_text(aes(x=0, y="y", label="label"), color="white", size=14, fontweight="bold")
-    + scale_fill_manual(values=colors)
-    + labs(title="funnel-basic · plotnine · pyplots.ai", x="", y="")
-    + theme_minimal()
+    ggplot(df_poly, aes(x="x", y="y", fill="stage", group="stage"))
+    + geom_polygon(color=PAGE_BG, size=2)
+    + geom_text(
+        aes(x="x", y="y", label="label", color="text_color"),
+        data=df_labels,
+        size=14,
+        fontweight="bold",
+        inherit_aes=False,
+    )
+    + scale_fill_manual(values=OKABE_ITO[:n_stages], guide=None)
+    + scale_color_identity()
+    + scale_y_reverse()
+    + labs(title="funnel-basic · plotnine · anyplot.ai", x="", y="")
+    + theme_void()
     + theme(
         figure_size=(16, 9),
-        plot_title=element_text(size=24, ha="center", weight="bold"),
+        plot_background=element_rect(fill=PAGE_BG, color=PAGE_BG),
+        panel_background=element_rect(fill=PAGE_BG, color=PAGE_BG),
+        plot_title=element_text(size=24, color=INK, weight="medium", ha="center"),
+        plot_margin=0.02,
         axis_text=element_blank(),
         axis_ticks=element_blank(),
         panel_grid=element_blank(),
@@ -68,4 +109,4 @@
 )
 
 # Save
-plot.save("plot.png", dpi=300, verbose=False)
+plot.save(f"plot-{THEME}.png", dpi=300, verbose=False)