Bug pylint 4326 (#1183)

* Adds unittest dealing with class subscript

* Adds support of type hints inside numpy's brains

* Adds unit test to check astroid does not crash if numpy is not available

3 files changed, 45 insertions, 5 deletions

diff --git a/astroid/brain/brain_numpy_core_numerictypes.py b/astroid/brain/brain_numpy_core_numerictypes.py
index 69c4686c..d52b1ed3 100644
--- a/astroid/brain/brain_numpy_core_numerictypes.py
+++ b/astroid/brain/brain_numpy_core_numerictypes.py
@@ -9,6 +9,7 @@
 # TODO(hippo91) : correct the methods signature.
 
 """Astroid hooks for numpy.core.numerictypes module."""
+from astroid.brain.brain_numpy_utils import numpy_supports_type_hints
 from astroid.brain.helpers import register_module_extender
 from astroid.builder import parse
 from astroid.manager import AstroidManager
@@ -19,9 +20,7 @@ def numpy_core_numerictypes_transform():
     #       According to numpy doc the generic object should expose
     #       the same API than ndarray. This has been done here partially
     #       through the astype method.
-    return parse(
-        """
-    # different types defined in numerictypes.py
+    generic_src = """
     class generic(object):
         def __init__(self, value):
             self.T = np.ndarray([0, 0])
@@ -106,8 +105,16 @@ def numpy_core_numerictypes_transform():
         def transpose(self): return uninferable
         def var(self): return uninferable
         def view(self): return uninferable
-
-
+        """
+    if numpy_supports_type_hints():
+        generic_src += """
+        @classmethod
+        def __class_getitem__(cls, value):
+            return cls
+        """
+    return parse(
+        generic_src
+        + """
     class dtype(object):
         def __init__(self, obj, align=False, copy=False):
             self.alignment = None
diff --git a/astroid/brain/brain_numpy_ndarray.py b/astroid/brain/brain_numpy_ndarray.py
index ea4fb809..bf588aa5 100644
--- a/astroid/brain/brain_numpy_ndarray.py
+++ b/astroid/brain/brain_numpy_ndarray.py
@@ -9,6 +9,7 @@
 
 
 """Astroid hooks for numpy ndarray class."""
+from astroid.brain.brain_numpy_utils import numpy_supports_type_hints
 from astroid.builder import extract_node
 from astroid.inference_tip import inference_tip
 from astroid.manager import AstroidManager
@@ -143,6 +144,12 @@ def infer_numpy_ndarray(node, context=None):
         def var(self, axis=None, dtype=None, out=None, ddof=0, keepdims=False): return np.ndarray([0, 0])
         def view(self, dtype=None, type=None): return np.ndarray([0, 0])
     """
+    if numpy_supports_type_hints():
+        ndarray += """
+        @classmethod
+        def __class_getitem__(cls, value):
+            return cls
+        """
     node = extract_node(ndarray)
     return node.infer(context=context)
 
diff --git a/astroid/brain/brain_numpy_utils.py b/astroid/brain/brain_numpy_utils.py
index 64a720b3..97c88e3f 100644
--- a/astroid/brain/brain_numpy_utils.py
+++ b/astroid/brain/brain_numpy_utils.py
@@ -8,9 +8,35 @@
 
 
 """Different utilities for the numpy brains"""
+from typing import Tuple
+
 from astroid.builder import extract_node
 from astroid.nodes.node_classes import Attribute, Import, Name, NodeNG
 
+# Class subscript is available in numpy starting with version 1.20.0
+NUMPY_VERSION_TYPE_HINTS_SUPPORT = ("1", "20", "0")
+
+
+def numpy_supports_type_hints() -> bool:
+    """
+    Returns True if numpy supports type hints
+    """
+    np_ver = _get_numpy_version()
+    return np_ver and np_ver > NUMPY_VERSION_TYPE_HINTS_SUPPORT
+
+
+def _get_numpy_version() -> Tuple[str, str, str]:
+    """
+    Return the numpy version number if numpy can be imported. Otherwise returns
+    ('0', '0', '0')
+    """
+    try:
+        import numpy  # pylint: disable=import-outside-toplevel
+
+        return tuple(numpy.version.version.split("."))
+    except ImportError:
+        return ("0", "0", "0")
+
 
 def infer_numpy_member(src, node, context=None):
     node = extract_node(src)