Revert "Cleanup utils.py"

This reverts commit 0e4c28d.

Author: dcherian

xarray/core/utils.py

@@ -10,6 +10,7 @@
 import warnings
 from enum import Enum
 from typing import (
+    TYPE_CHECKING,
     Any,
     Callable,
     Collection,
@@ -306,18 +307,35 @@ def _is_scalar(value, include_0d):
     )
 
 
-if sys.version_info >= (3, 10):
-    from typing import TypeGuard
-else:
-    from typing_extensions import TypeGuard
+# See GH5624, this is a convoluted way to allow type-checking to use `TypeGuard` without
+# requiring typing_extensions as a required dependency to _run_ the code (it is required
+# to type-check).
+try:
+    if sys.version_info >= (3, 10):
+        from typing import TypeGuard
+    else:
+        from typing_extensions import TypeGuard
+except ImportError:
+    if TYPE_CHECKING:
+        raise
+    else:
 
+        def is_scalar(value: Any, include_0d: bool = True) -> bool:
+            """Whether to treat a value as a scalar.
 
-def is_scalar(value: Any, include_0d: bool = True) -> TypeGuard[Hashable]:
-    """Whether to treat a value as a scalar.
+            Any non-iterable, string, or 0-D array
+            """
+            return _is_scalar(value, include_0d)
 
-    Any non-iterable, string, or 0-D array
-    """
-    return _is_scalar(value, include_0d)
+
+else:
+
+    def is_scalar(value: Any, include_0d: bool = True) -> TypeGuard[Hashable]:
+        """Whether to treat a value as a scalar.
+
+        Any non-iterable, string, or 0-D array
+        """
+        return _is_scalar(value, include_0d)
 
 
 def is_valid_numpy_dtype(dtype: Any) -> bool: