Bug: draw.py hard-imports cv2/vsketch/rasterio at top-level — missing dep = opaque crash

Bug: draw.py hard-imports cv2/vsketch/rasterio at top-level — missing dep = opaque crash

Describe the bug

draw.py imports all heavy dependencies at module level (lines 31–42). If any single dependency is missing, import prettymaps fails completely with a bare ModuleNotFoundError that doesn't indicate which package is needed or whether it's optional.

To reproduce

pip install prettymaps --no-deps
python -c "import prettymaps"
# → ModuleNotFoundError: No module named 'cv2'
# (install cv2, retry)
# → ModuleNotFoundError: No module named 'vsketch'
# (install vsketch, retry)
# → ModuleNotFoundError: No module named 'rasterio'

Expected behavior

Basic matplotlib rendering should work without requiring cv2, rasterio, vsketch, elevation, scikit-image, etc. Optional dependencies should be imported lazily inside the functions that need them.

Root cause

# draw.py lines 31-42 (all top-level, all unconditional):
import cv2                    # opencv-python-headless — only needed for postprocessing
import geopandas as gp
import matplotlib
import numpy as np
import osmnx as ox
import pandas as pd
import shapely.affinity
import shapely.ops
import vsketch                # only needed for vsketch mode
from matplotlib import pyplot as plt
from matplotlib.colors import LightSource

rasterio, rioxarray, scikit-image, elevation are also imported but only needed for elevation/terrain features.

Suggested fix

Lazy-import heavy/optional dependencies inside the functions that need them:

def plot(..., mode="matplotlib"):
    if mode == "vsketch":
        import vsketch
    # ...

This lets users render basic matplotlib maps without installing the full dependency tree. It also improves import time (currently 10+ seconds on first import due to matplotlib font cache scan when MPLCONFIGDIR is unset).

Environment

• prettymaps v1.4.2
• Python 3.10.18 (Homebrew)
• macOS 15, ARM64