ucontextlib: spin off minimal module from contextlib

ucontextlib/metadata.txt

@@ -0,0 +1,5 @@
+srctype = micropython-lib
+type = module
+version = 0.1
+license = Python
+long_desc = Minimal subset of contextlib for MicroPython low-memory ports

ucontextlib/setup.py

@@ -0,0 +1,18 @@
+import sys
+# Remove current dir from sys.path, otherwise setuptools will peek up our
+# module instead of system.
+sys.path.pop(0)
+from setuptools import setup
+
+
+setup(name='micropython-ucontextlib',
+      version='0.1',
+      description='ucontextlib module for MicroPython',
+      long_description='Minimal subset of contextlib for MicroPython low-memory ports',
+      url='https://github.com/micropython/micropython/issues/405',
+      author='MicroPython Developers',
+      author_email='micro-python@googlegroups.com',
+      maintainer='MicroPython Developers',
+      maintainer_email='micro-python@googlegroups.com',
+      license='Python',
+      py_modules=['ucontextlib'])

ucontextlib/tests.py

@@ -0,0 +1,36 @@
+import unittest
+from ucontextlib import contextmanager
+
+
+class ContextManagerTestCase(unittest.TestCase):
+
+    def setUp(self):
+        self._history = []
+
+        @contextmanager
+        def manager(x):
+            self._history.append('start')
+            try:
+                yield x
+            finally:
+                self._history.append('finish')
+
+        self._manager = manager
+
+    def test_context_manager(self):
+        with self._manager(123) as x:
+            self.assertEqual(x, 123)
+        self.assertEqual(self._history, ['start', 'finish'])
+
+    def test_context_manager_on_error(self):
+        exc = Exception()
+        try:
+            with self._manager(123) as x:
+                raise exc
+        except Exception as e:
+            self.assertEqual(exc, e)
+        self.assertEqual(self._history, ['start', 'finish'])
+
+
+if __name__ == '__main__':
+    unittest.main()

ucontextlib/ucontextlib.py

@@ -0,0 +1,106 @@
+"""Utilities for with-statement contexts.  See PEP 343.
+
+Original source code: https://hg.python.org/cpython/file/3.4/Lib/contextlib.py
+
+Not implemented:
+ - redirect_stdout;
+ - ExitStack.
+ - closing
+ - supress
+"""
+
+class ContextDecorator(object):
+    "A base class or mixin that enables context managers to work as decorators."
+
+    def _recreate_cm(self):
+        """Return a recreated instance of self.
+
+        Allows an otherwise one-shot context manager like
+        _GeneratorContextManager to support use as
+        a decorator via implicit recreation.
+
+        This is a private interface just for _GeneratorContextManager.
+        See issue #11647 for details.
+        """
+        return self
+
+    def __call__(self, func):
+        def inner(*args, **kwds):
+            with self._recreate_cm():
+                return func(*args, **kwds)
+        return inner
+
+
+class _GeneratorContextManager(ContextDecorator):
+    """Helper for @contextmanager decorator."""
+
+    def __init__(self, func, *args, **kwds):
+        self.gen = func(*args, **kwds)
+        self.func, self.args, self.kwds = func, args, kwds
+
+    def _recreate_cm(self):
+        # _GCM instances are one-shot context managers, so the
+        # CM must be recreated each time a decorated function is
+        # called
+        return self.__class__(self.func, *self.args, **self.kwds)
+
+    def __enter__(self):
+        try:
+            return next(self.gen)
+        except StopIteration:
+            raise RuntimeError("generator didn't yield") from None
+
+    def __exit__(self, type, value, traceback):
+        if type is None:
+            try:
+                next(self.gen)
+            except StopIteration:
+                return
+            else:
+                raise RuntimeError("generator didn't stop")
+        else:
+            if value is None:
+                # Need to force instantiation so we can reliably
+                # tell if we get the same exception back
+                value = type()
+            try:
+                self.gen.throw(type, value, traceback)
+                raise RuntimeError("generator didn't stop after throw()")
+            except StopIteration as exc:
+                # Suppress the exception *unless* it's the same exception that
+                # was passed to throw().  This prevents a StopIteration
+                # raised inside the "with" statement from being suppressed
+                return exc is not value
+
+
+def contextmanager(func):
+    """@contextmanager decorator.
+
+    Typical usage:
+
+        @contextmanager
+        def some_generator(<arguments>):
+            <setup>
+            try:
+                yield <value>
+            finally:
+                <cleanup>
+
+    This makes this:
+
+        with some_generator(<arguments>) as <variable>:
+            <body>
+
+    equivalent to this:
+
+        <setup>
+        try:
+            <variable> = <value>
+            <body>
+        finally:
+            <cleanup>
+
+    """
+    def helper(*args, **kwds):
+        return _GeneratorContextManager(func, *args, **kwds)
+    return helper