contexts: added 'breakable_section'

Author: koreno

easypy/contexts.py

@@ -107,3 +107,37 @@ def some_other_context_manager():
 
 def is_contextmanager(func):
     return getattr(func, "__code__", None) in _ctxm_code_samples
+
+
+@contextmanager
+def breakable_section():
+    """
+    Useful for getting out of some deep nesting, as an alternative to a closure:
+
+        item = None
+        with breakable_section() as Break:
+            if alpha:
+                item = alpha.value
+                raise Break
+
+            if beta:
+                for opt in beta.items:
+                    if opt.is_the_one:
+                        item = opt.value
+                        raise Break
+
+    Note that each 'Break' class this context-manager yield is unique,
+    i.e it will only be caught by the context-manager that created it:
+
+        with breakable_section() as Break1:
+
+            with breakable_section() as Break2:
+                raise Break1
+
+            assert False  # will not reach here
+    """
+    Break = type("Break", (Exception,), {})
+    try:
+        yield Break
+    except Break:
+        pass

tests/test_contexts.py

@@ -1,5 +1,5 @@
 import pytest
-from easypy.contexts import contextmanager
+from easypy.contexts import contextmanager, breakable_section
 
 
 X = []
@@ -47,3 +47,21 @@ def foo():
         assert X == [1]
 
     assert not X
+
+
+def test_breakable_section():
+
+    a = []
+    with breakable_section() as Break1:
+        with breakable_section() as Break2:
+            with breakable_section() as Break3:
+                raise Break2()
+                a += [1]  # this will be skipped
+            a += [2]  # this will be skipped
+        a += [3]  # landing here
+    a += [4]
+
+    assert Break1 is not Break2
+    assert Break2 is not Break3
+    assert Break3 is not Break1
+    assert a == [3, 4]