Do not define `self._ishape_last`

Do not define `self._ishape_last[i_slice][orientation]` in
`_create_ishape_last`. Return a numpy array instead. Clearer.

Common/util_eddies.py

@@ -160,7 +160,9 @@ class SHPC_class:
             except OSError:
                 print("Could not read", fname)
                 print("Creating it...")
-                self._create_ishape_last(i_slice, orientation)
+                self._ishape_last[i_slice][
+                    orientation
+                ] = self._create_ishape_last(i_slice, orientation)
 
             if self._ishape_last[i_slice][orientation] is not None:
                 assert self._ishape_last[i_slice][orientation].size != 0
@@ -195,9 +197,8 @@ class SHPC_class:
         return self._n_shapes[i_slice][orientation]
 
     def _create_ishape_last(self, i_slice, orientation):
-        """Defines self._ishape_last[i_slice][orientation], which is a numpy
-        array, and creates the file ishape_last.txt. Can fail if it
-        cannot get a reader.
+        """Creates the file ishape_last.txt and returns the corresponding
+        numpy array. Returns None if it cannot get a reader.
 
         """
 
@@ -207,6 +208,7 @@ class SHPC_class:
 
         if reader is None:
             print('Could not create "ishape_last.txt".')
+            ishape_last = None
         else:
             for ishape, rec in enumerate(reader.iterRecords(fields=["date"])):
                 if rec.date != last_date:
@@ -225,13 +227,13 @@ class SHPC_class:
             for repet_factor, ishape in date_ishape:
                 ishape_last.extend(repet_factor * [ishape])
 
-            self._ishape_last[i_slice][orientation] = np.array(ishape_last)
+            ishape_last = np.array(ishape_last)
             fname = path.join(
                 self.dir, f"Slice_{i_slice}", orientation, "ishape_last.txt"
             )
-            np.savetxt(
-                fname, self._ishape_last[i_slice][orientation], fmt="%.0d"
-            )
+            np.savetxt(fname, ishape_last, fmt="%.0d")
+
+        return ishape_last
 
     def get_slice(self, date_index):
         i_slice = bisect.bisect(self.d_init, date_index) - 1