Format state_spec in the error message (keras-team#9035)

* Implement __repr__ for InputSpec

* Error message

keras/engine/topology.py

@@ -65,6 +65,15 @@ def __init__(self, dtype=None,
         self.min_ndim = min_ndim
         self.axes = axes or {}
 
+    def __repr__(self):
+        spec = [('dtype=' + str(self.dtype)) if self.dtype else '',
+                ('shape=' + str(self.shape)) if self.shape else '',
+                ('ndim=' + str(self.ndim)) if self.ndim else '',
+                ('max_ndim=' + str(self.max_ndim)) if self.max_ndim else '',
+                ('min_ndim=' + str(self.min_ndim)) if self.min_ndim else '',
+                ('axes=' + str(self.axes)) if self.axes else '']
+        return 'InputSpec(%s)' % ', '.join(x for x in spec if x)
+
 
 class Node(object):
     """A `Node` describes the connectivity between two layers.

keras/layers/recurrent.py

@@ -459,9 +459,9 @@ def build(self, input_shape):
             # initial_state was passed in call, check compatibility
             if [spec.shape[-1] for spec in self.state_spec] != state_size:
                 raise ValueError(
-                    'An initial_state was passed that is not compatible with '
+                    'An `initial_state` was passed that is not compatible with '
                     '`cell.state_size`. Received `state_spec`={}; '
-                    'However `cell.state_size` is '
+                    'however `cell.state_size` is '
                     '{}'.format(self.state_spec, self.cell.state_size))
         else:
             self.state_spec = [InputSpec(shape=(None, dim))