Rename keys of readers

Make them equal to basenames of shapefiles. Clearer and allows a
little simplification in programming.

Analysis/plot_eddy_contours.py

@@ -65,11 +65,11 @@ def snapshot(ax, ishape_list, readers, *, dashed = False, light = False,
     dashed: boolean."""
     
     for ishape in ishape_list:
-        shape_rec_extr = readers["extr"].shapeRecord(ishape)
-        shape_outer = readers["outer"].shape(ishape)
+        shape_rec_extr = readers["extremum"].shapeRecord(ishape)
+        shape_outer = readers["outermost_contour"].shape(ishape)
 
-        if "m_s" in readers:
-            shape_m_s = readers["m_s"].shape(ishape)
+        if "max_speed_contour" in readers:
+            shape_m_s = readers["max_speed_contour"].shape(ishape)
         else:
             shape_m_s = None
 
@@ -184,12 +184,12 @@ def compute_bbox(ishape_lists, reader_outer):
 
 def make_animation(fig, ax, k1, ishape_last, readers, window, k_min, k_max,
                    light):
-    ishape_lists = {k: select_ishapes(k, k1, ishape_last, readers["extr"],
+    ishape_lists = {k: select_ishapes(k, k1, ishape_last, readers["extremum"],
                                       window)
                     for k in range(k_min, k_max + 1)}
 
     if window is None:
-        bbox = compute_bbox(ishape_lists, readers["outer"])
+        bbox = compute_bbox(ishape_lists, readers["outermost_contour"])
     else:
         bbox = window
 
@@ -200,18 +200,15 @@ def make_animation(fig, ax, k1, ishape_last, readers, window, k_min, k_max,
     return ani
 
 def open_shpt(shp_coll_dir):
-    readers = {"extr": shapefile.Reader(path.join(shp_coll_dir, "extremum")),
-               "outer":
-               shapefile.Reader(path.join(shp_coll_dir, "outermost_contour"))}
-
-    try:
-        readers["m_s"] = shapefile.Reader(path.join(shp_coll_dir,
-                                                    "max_speed_contour"))
-    except shapefile.ShapefileException:
-        print("Shapefile max_speed_contour not found. "
-              "Max-speed contours will not be plotted.")
+    readers = {}
+    
+    for layer in ["extremum", "outermost_contour", "max_speed_contour"]:
+        try:
+            readers[layer] = shapefile.Reader(path.join(shp_coll_dir, layer))
+        except shapefile.ShapefileException:
+            print(f"Shapefile {layer} not found.")
 
-    k1 = readers["extr"].record(0).date_index
+    k1 = readers["extremum"].record(0).date_index
     fname = path.join(shp_coll_dir, "ishape_last.txt")
     
     try:
@@ -219,7 +216,7 @@ def open_shpt(shp_coll_dir):
     except OSError:
         print("Could not read", fname)
         print("We will use all the shapes.")
-        ishape_last = [len(readers["extr"]) - 1]
+        ishape_last = [len(readers["extremum"]) - 1]
 
     return readers, k1, ishape_last
 
@@ -302,7 +299,7 @@ if __name__ == "__main__":
                     marker = "+", color = "gray", linestyle = "None")
 
         if args.window is None: plot_grid_bb(args.shp_coll_dir, ax)
-        ishape_list = select_ishapes(k, k1, ishape_last, readers["extr"],
+        ishape_list = select_ishapes(k, k1, ishape_last, readers["extremum"],
                                      args.window)
         ax.set_title(f"k = {k}", y = 1.05)
         snapshot(ax, ishape_list, readers, dashed = args.dashed,