Generalize `filter.py` for several dates

Generalize `filter.py` to act on a triplet of shapefiles containing
several dates, with renumber option. Create file `ishape_last.txt`.

Analysis/filter.py

 #!/usr/bin/env python3
 
+"""Note: the creation of ishape_last.txt assumes no missing date in
+the output."""
+
 import shapefile
 import argparse
 from os import path
@@ -7,9 +10,9 @@ from os import path
 def accept(shape_rec_extr, shape_rec_outer, shape_rec_max):
     """Filtering function."""
     
-    # return 6 <= shape_rec_extr.shape.points[0][0] <= 12 \
-    #        and - 33 <= shape_rec_extr.shape.points[0][1] <= - 27
-    return shape_rec_extr.record.date_index == 20456
+    return 1.625 <= shape_rec_extr.shape.points[0][0] <= 15.625 \
+        and - 38.375 <= shape_rec_extr.shape.points[0][1] <= - 30.375
+    ##return shape_rec_extr.record.date_index == 20456
 
 parser = argparse.ArgumentParser()
 parser.add_argument("input_dir", help = "containing the three input shapefiles")
@@ -33,12 +36,21 @@ with shapefile.Reader(path.join(args.input_dir, "extremum")) as extremum, \
     extremum_filt.fields = extremum.fields[1:]
     outermost_cont_filt.fields = outermost_cont.fields[1:]
     max_speed_cont_filt.fields = max_speed_cont.fields[1:]
-    if args.renumber: eddy_index = 0
-
+    
+    if args.renumber:
+        last_date_written = None
+        ishape_last = []
+        
     for shape_rec_extr, shape_rec_outer, shape_rec_max \
         in zip(extremum, outermost_cont, max_speed_cont):
         if accept(shape_rec_extr, shape_rec_outer, shape_rec_max):
-            if args.renumber: eddy_index += 1
+            if args.renumber:
+                if shape_rec_extr.record.date_index == last_date_written:
+                    eddy_index += 1
+                else:
+                    ishape_last.append((len(extremum_filt) - 1))
+                    eddy_index = 1
+                    last_date_written = shape_rec_extr.record.date_index
 
             for sr, w in zip([shape_rec_extr, shape_rec_outer, shape_rec_max],
                              [extremum_filt, outermost_cont_filt,
@@ -47,3 +59,12 @@ with shapefile.Reader(path.join(args.input_dir, "extremum")) as extremum, \
                 if args.renumber: r["eddy_index"] = eddy_index
                 w.record(*r)
                 w.shape(sr.shape)
+
+    if args.renumber:
+        ishape_last.append((len(extremum_filt) - 1))
+        file = path.join(args.output_dir, "ishape_last.txt")
+        
+        with open(file, "w") as f:
+            for i in ishape_last[1:]:
+                f.write(str(i) + "\n")
+