Merge pull request #83 from ikalnytskyi/bug/pop-runtimeerror

Throw RuntimeError from .pop() when stack is empty

docs/index.rst

@@ -367,6 +367,11 @@ Release Notes
   lost its coroutine function marker, i.e. ``inspect.iscoroutinefunction()``
   returned ``False``.
 
+* Fix a bug when ``picobox.pop()`` threw a generic ``IndexError`` when there
+  were no pushed boxes on stack. Now ``RuntimeError`` exception is thrown
+  instead with a good-looking error message. The behavior is now consistent
+  with other functions such as ``picobox.put()`` or ``picobox.get()``.
+
 4.0.0
 `````
 

src/picobox/_stack.py

@@ -7,6 +7,8 @@
 
 from ._box import Box, ChainBox
 
+_ERROR_MESSAGE_EMPTY_STACK = "No boxes found on the stack, please `.push()` a box first."
+
 
 def _copy_signature(method, instance=None):
     # This is a workaround to overcome 'sphinx.ext.autodoc' inability to
@@ -23,15 +25,15 @@ def _copy_signature(method, instance=None):
     return functools.wraps(method, (), ())
 
 
-def _create_stack_proxy(stack, empty_stack_error):
+def _create_stack_proxy(stack):
     """Create an object that proxies all calls to the top of the stack."""
 
     class _StackProxy:
         def __getattribute__(self, name):
             try:
                 return getattr(stack[-1], name)
             except IndexError:
-                raise RuntimeError(empty_stack_error)
+                raise RuntimeError(_ERROR_MESSAGE_EMPTY_STACK)
 
     return _StackProxy()
 
@@ -103,9 +105,7 @@ def __init__(self, name: t.Optional[str] = None):
         # that mimic Box interface but deal with a box on the top instead.
         # While it's not completely necessary for `put()` and `get()`, it's
         # crucial for `pass_()` due to its laziness and thus late evaluation.
-        self._topbox = _create_stack_proxy(
-            self._stack, "No boxes found on the stack, please `.push()` a box first."
-        )
+        self._topbox = _create_stack_proxy(self._stack)
 
     def __repr__(self):
         name = self._name
@@ -157,7 +157,10 @@ def pop(self) -> Box:
         # ensure the code works properly even when running on alternative
         # implementations.
         with self._lock:
-            return self._stack.pop()
+            try:
+                return self._stack.pop()
+            except IndexError:
+                raise RuntimeError(_ERROR_MESSAGE_EMPTY_STACK)
 
     @_copy_signature(Box.put)
     def put(self, *args, **kwargs):

tests/test_stack.py

@@ -733,8 +733,8 @@ def fn(magic):
     assert teststack.pop() is foobox
 
 
-def test_stack_pop_indexerror(teststack):
-    with pytest.raises(IndexError) as excinfo:
+def test_stack_pop_runtimeerror(teststack):
+    with pytest.raises(RuntimeError) as excinfo:
         teststack.pop()
 
-    assert str(excinfo.value) == "pop from empty list"
+    assert str(excinfo.value) == "No boxes found on the stack, please `.push()` a box first."