Provide exception message and change exception type

Author: oscargus

doc/api/next_api_changes/behavior/23550-OG.rst

@@ -0,0 +1,10 @@
+Specified exception types in Grid
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In a few cases an `Exception` was thrown when an incorrect argument value
+was set in the `mpl_toolkits.axes_grid1.axes_grid.Grid`
+(= `mpl_toolkits.axisartist.axes_grid.Grid`) constructor. These are replaced
+as follows:
+
+* Providing an incorrect value for *ngrids* now raises a `ValueError`
+* Providing an incorrect type for *rect* now raises a `TypeError`

lib/mpl_toolkits/axes_grid1/axes_grid.py

@@ -123,7 +123,8 @@ def __init__(self, fig,
             ngrids = self._nrows * self._ncols
         else:
             if not 0 < ngrids <= self._nrows * self._ncols:
-                raise Exception("")
+                raise ValueError(
+                    "ngrids must be positive and not larger than nrows*ncols")
 
         self.ngrids = ngrids
 
@@ -147,7 +148,7 @@ def __init__(self, fig,
         elif len(rect) == 4:
             self._divider = Divider(fig, rect, **kw)
         else:
-            raise Exception("")
+            raise TypeError("Incorrect rect format")
 
         rect = self._divider.get_position()