Multithread satellite imagery downloading

scripts/download_satellite.py

@@ -6,18 +6,23 @@
 import os
 import urllib.request
 from PIL import Image
+from concurrent.futures import ThreadPoolExecutor
 
 MAX_ZOOM=20
 
+def download_all():
     current, total = 0, (4 ** (MAX_ZOOM - 11) - 1)//3
-
+    with ThreadPoolExecutor() as executor:
         for z in range(12, MAX_ZOOM + 1):
             scale = 2 ** (z - 12)
             start_x = 985 * scale
             start_y = 1432 * scale
             for x in range(start_x, start_x + scale):
                 for y in range(start_y, start_y + scale):
+                    executor.submit(download_image, z, x, y, total, current)
                     current += 1
+
+def download_image(z, x, y, total, current):
     progress = f"[{current:0{len(str(total))}d}/{total}]"
     url = f"https://svc.pictometry.com/Image/D2B06344-7A2D-5BD0-FC89-DFDDC9888C41/wmts/PICT-MNITAS23-EDVs7UTOVt/default/GoogleMapsCompatible/{z}/{x}/{y}.png"
     file = os.path.normpath(os.path.join(os.path.dirname(__file__), f"../satellite/{z}/{x}/{y}.png"))
@@ -26,9 +31,11 @@ for z in range(12, MAX_ZOOM+1):
         try: # does it already exist and look good?
             Image.open(file).verify() # CRC check on PNGs; nothing on other file types? https://pillow.readthedocs.io/en/latest/_modules/PIL/PngImagePlugin.html#ChunkStream.verify
             print(f"{progress} {file} already exists; skipping")
-                    continue
+            return
         except OSError as e:
             print(f"{progress} replacing corrupt {file}")
     else:
         print(f"{progress} downloading {file}")
     urllib.request.urlretrieve(url, file)
+
+download_all()