[MRG+1] FIX Add some validation in the constructor of ParameterGrid (scikit-learn#11090)

Author: SolutusImmensus

doc/whats_new/v0.20.rst

@@ -615,6 +615,9 @@ Misc
   acts as an upper bound on iterations.
   :issue:`#10982` by :user:`Juliet Lawton <julietcl>`
 
+- Invalid input for :class:`model_selection.ParameterGrid` now raises TypeError.
+  :issue:`10928` by :user:`Solutus Immensus <solutusimmensus>`
+
 Changes to estimator checks
 ---------------------------
 

sklearn/model_selection/_search.py

@@ -13,7 +13,7 @@
 # License: BSD 3 clause
 
 from abc import ABCMeta, abstractmethod
-from collections import Mapping, namedtuple, defaultdict, Sequence
+from collections import Mapping, namedtuple, defaultdict, Sequence, Iterable
 from functools import partial, reduce
 from itertools import product
 import operator
@@ -90,10 +90,26 @@ class ParameterGrid(object):
     """
 
     def __init__(self, param_grid):
+        if not isinstance(param_grid, (Mapping, Iterable)):
+            raise TypeError('Parameter grid is not a dict or '
+                            'a list ({!r})'.format(param_grid))
+
         if isinstance(param_grid, Mapping):
             # wrap dictionary in a singleton list to support either dict
             # or list of dicts
             param_grid = [param_grid]
+
+        # check if all entries are dictionaries of lists
+        for grid in param_grid:
+            if not isinstance(grid, dict):
+                raise TypeError('Parameter grid is not a '
+                                'dict ({!r})'.format(grid))
+            for key in grid:
+                if not isinstance(grid[key], Iterable):
+                    raise TypeError('Parameter grid value is not iterable '
+                                    '(key={!r}, value={!r})'
+                                    .format(key, grid[key]))
+
         self.param_grid = param_grid
 
     def __iter__(self):

sklearn/model_selection/tests/test_search.py

@@ -12,6 +12,7 @@
 
 import numpy as np
 import scipy.sparse as sp
+import pytest
 
 from sklearn.utils.fixes import sp_version
 from sklearn.utils.testing import assert_equal
@@ -126,7 +127,19 @@ def assert_grid_iter_equals_getitem(grid):
     assert_equal(list(grid), [grid[i] for i in range(len(grid))])
 
 
+@pytest.mark.parametrize(
+    "input, error_type, error_message",
+    [(0, TypeError, 'Parameter grid is not a dict or a list (0)'),
+     ([{'foo': [0]}, 0], TypeError, 'Parameter grid is not a dict (0)'),
+     ({'foo': 0}, TypeError, "Parameter grid value is not iterable "
+      "(key='foo', value=0)")]
+)
+def test_validate_parameter_grid_input(input, error_type, error_message):
+    with pytest.raises(error_type, message=error_message):
+        ParameterGrid(input)
+
 def test_parameter_grid():
+
     # Test basic properties of ParameterGrid.
     params1 = {"foo": [1, 2, 3]}
     grid1 = ParameterGrid(params1)