feat(altair): implement errorbar-basic (#5385)

## Implementation: `errorbar-basic` - python/altair

Implements the **python/altair** version of `errorbar-basic`.

**File:** `plots/errorbar-basic/implementations/python/altair.py`

**Parent Issue:** #973

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/24927121489)*

---------

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/errorbar-basic/implementations/python/altair.py

@@ -1,24 +1,38 @@
-""" pyplots.ai
+""" anyplot.ai
 errorbar-basic: Basic Error Bar Plot
-Library: altair 6.0.0 | Python 3.13.11
-Quality: 92/100 | Created: 2025-12-23
+Library: altair 6.1.0 | Python 3.14.4
+Quality: 88/100 | Updated: 2026-04-25
 """
 
-import altair as alt
-import numpy as np
-import pandas as pd
+import importlib
+import os
+import sys
 
 
-# Data - experimental measurements with associated uncertainties
+# Drop script directory from sys.path so the `altair` package resolves, not this file
+sys.path[:] = [p for p in sys.path if os.path.abspath(p or ".") != os.path.dirname(os.path.abspath(__file__))]
+alt = importlib.import_module("altair")
+np = importlib.import_module("numpy")
+pd = importlib.import_module("pandas")
+
+
+# Theme tokens
+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"
+BRAND = "#009E73"  # Okabe-Ito position 1
+
+# Data
 np.random.seed(42)
 categories = ["Control", "Treatment A", "Treatment B", "Treatment C", "Treatment D", "Treatment E"]
 y_values = [25.3, 38.7, 42.1, 35.8, 48.2, 31.5]
 
-# Asymmetric errors: Treatment C and D have notably different lower/upper bounds
+# Asymmetric errors: Treatment C and D show notably different lower/upper bounds
 asymmetric_lower = [2.1, 3.5, 2.8, 6.5, 4.8, 2.5]
 asymmetric_upper = [2.1, 3.5, 2.8, 2.8, 2.2, 2.5]
 
-# Create DataFrame with error bounds
 df = pd.DataFrame(
     {
         "category": categories,
@@ -28,43 +42,55 @@
     }
 )
 
-# Base chart with shared properties
-base = alt.Chart(df).encode(
-    x=alt.X(
-        "category:N",
-        title="Experimental Group",
-        sort=categories,
-        axis=alt.Axis(labelFontSize=18, titleFontSize=22, labelAngle=0),
-    )
-)
+# Plot
+y_scale = alt.Scale(domain=[15, 55], nice=False)
+y_title = "Response Value (units)"
 
-# Points for the central values
-points = base.mark_circle(size=300, color="#306998").encode(
-    y=alt.Y(
-        "value:Q",
-        title="Response Value (units)",
-        scale=alt.Scale(domain=[0, 55]),
-        axis=alt.Axis(labelFontSize=18, titleFontSize=22, grid=True, gridOpacity=0.3, gridDash=[4, 4]),
-    )
-)
+base = alt.Chart(df).encode(x=alt.X("category:N", title="Experimental Group", sort=categories))
 
-# Error bars using mark_rule with y and y2
-error_bars = base.mark_rule(strokeWidth=3, color="#306998").encode(y=alt.Y("error_lower:Q"), y2="error_upper:Q")
+error_bars = base.mark_rule(strokeWidth=3, color=BRAND).encode(
+    y=alt.Y("error_lower:Q", title=y_title, scale=y_scale), y2="error_upper:Q"
+)
 
-# Error bar caps (top)
-caps_top = base.mark_tick(thickness=3, size=20, color="#306998").encode(y="error_upper:Q")
+caps_top = base.mark_tick(thickness=3, size=22, color=BRAND).encode(
+    y=alt.Y("error_upper:Q", title=y_title, scale=y_scale)
+)
+caps_bottom = base.mark_tick(thickness=3, size=22, color=BRAND).encode(
+    y=alt.Y("error_lower:Q", title=y_title, scale=y_scale)
+)
 
-# Error bar caps (bottom)
-caps_bottom = base.mark_tick(thickness=3, size=20, color="#306998").encode(y="error_lower:Q")
+points = base.mark_circle(size=320, color=BRAND).encode(
+    y=alt.Y("value:Q", title=y_title, scale=y_scale),
+    tooltip=[
+        alt.Tooltip("category:N", title="Group"),
+        alt.Tooltip("value:Q", title="Mean", format=".2f"),
+        alt.Tooltip("error_lower:Q", title="Lower bound", format=".2f"),
+        alt.Tooltip("error_upper:Q", title="Upper bound", format=".2f"),
+    ],
+)
 
-# Layer all elements
 chart = (
     alt.layer(error_bars, caps_bottom, caps_top, points)
-    .properties(width=1600, height=900, title=alt.Title("errorbar-basic · altair · pyplots.ai", fontSize=28))
-    .configure_axis(labelFontSize=18, titleFontSize=22)
-    .configure_view(strokeWidth=0)
+    .properties(
+        width=1600,
+        height=900,
+        background=PAGE_BG,
+        title=alt.Title("errorbar-basic · altair · anyplot.ai", fontSize=28, color=INK, anchor="start", offset=20),
+    )
+    .configure_view(fill=PAGE_BG, stroke=None)
+    .configure_axis(
+        labelFontSize=18,
+        titleFontSize=22,
+        labelColor=INK_SOFT,
+        titleColor=INK,
+        domainColor=INK_SOFT,
+        tickColor=INK_SOFT,
+        gridColor=INK,
+        gridOpacity=0.10,
+        labelAngle=0,
+    )
+    .configure_legend(fillColor=ELEVATED_BG, strokeColor=INK_SOFT, labelColor=INK_SOFT, titleColor=INK)
 )
 
-# Save
-chart.save("plot.png", scale_factor=3.0)
-chart.save("plot.html")
+chart.save(f"plot-{THEME}.png", scale_factor=3.0)
+chart.save(f"plot-{THEME}.html")