adding required wrapper (#1056)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

CHANGELOG.md

@@ -8,7 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
--
+- Added `requires` wrapper ([#1056](https://github.com/PyTorchLightning/pytorch-lightning-bolts/pull/1056))
 
 
 ### Changed

src/pl_bolts/utils/_dependency.py

@@ -0,0 +1,28 @@
+import functools
+import os
+from typing import Any, Callable
+
+from lightning_utilities.core.imports import ModuleAvailableCache, RequirementCache
+
+
+# ToDo: replace with utils wrapper after 0.10 is released
+def requires(*module_path_version: str) -> Callable:
+    """Wrapper for enforcing certain requirements for a particular class or function."""
+
+    def decorator(func: Callable) -> Callable:
+        reqs = [
+            ModuleAvailableCache(mod_ver) if "." in mod_ver else RequirementCache(mod_ver)
+            for mod_ver in module_path_version
+        ]
+        available = all(map(bool, reqs))
+        if not available:
+
+            @functools.wraps(func)
+            def wrapper(*args: Any, **kwargs: Any) -> Any:
+                msg = os.linesep.join([repr(r) for r in reqs if not bool(r)])
+                raise ModuleNotFoundError(f"Required dependencies not available: \n{msg}")
+
+            return wrapper
+        return func
+
+    return decorator

tests/utils/test_dependency.py

@@ -0,0 +1,28 @@
+import pytest
+from pl_bolts.utils._dependency import requires
+
+
+@requires("torch")
+def using_torch():
+    return True
+
+
+@requires("torch.anything.wrong")
+def using_torch_wrong_path():
+    return True
+
+
+@requires("torch>99.0")
+def using_torch_bad_version():
+    return True
+
+
+def test_requires_pass():
+    assert using_torch() is True
+
+
+def test_requires_fail():
+    with pytest.raises(ModuleNotFoundError, match="Required dependencies not available"):
+        assert using_torch_wrong_path()
+    with pytest.raises(ModuleNotFoundError, match="Required dependencies not available"):
+        assert using_torch_bad_version()