Version 0.5.0 pre-release

Author: sobolevn

CHANGELOG.md

@@ -7,7 +7,10 @@ We follow Semantic Versions since the `0.1.0` release.
 
 ### Features
 
-- Adds `compose` function
+- Adds `compose` helper function
+- Adds public API to `import returns`
+- Adds `raise_exception` helper function
+- Adds full traceback to `.unwrap()`
 
 
 ### Misc

docs/pages/functions.rst

@@ -221,6 +221,44 @@ Composition is also type-safe.
 The only limitation is that we only support
 functions with one argument and one return to be composed.
 
+
+raise_exception
+---------------
+
+Sometimes you really want to reraise an exception from ``Failure[Exception]``
+due to some existing API (or a dirty hack).
+
+We allow you to do that with ease!
+
+.. code:: python
+
+  from returns.functions import raise_exception
+
+  class CreateAccountAndUser(object):
+      """Creates new Account-User pair."""
+
+      @pipeline
+      def __call__(self, username: str) -> ...:
+          """Imagine, that you need to reraise ValidationErrors due to API."""
+          user_schema = self._validate_user(
+            username,
+          ).fix(
+            # What happens here is interesting, since you do not let your
+            # unwrap to fail with UnwrapFailedError, but instead
+            # allows you to reraise a wrapped exception.
+            # In this case `ValidationError()` will be thrown
+            # before `UnwrapFailedError`
+            raise_exception,
+          ).unwrap()
+
+      def _validate_user(
+        self, username: str,
+      ) -> Result['User', ValidationError]:
+        ...
+
+Use this with caution. We try to remove exceptions from our code base.
+Original proposal is `here <https://github.com/dry-python/returns/issues/56>`_.
+
 API Reference
 -------------
 

returns/__init__.py

@@ -1 +1,28 @@
 # -*- coding: utf-8 -*-
+
+"""
+We define public API here.
+
+So, later our code can be used like so:
+
+.. code:: python
+
+  import returns
+  result: returns.Result[int, str]
+
+See: https://github.com/dry-python/returns/issues/73
+"""
+
+from returns.functions import compose, safe, pipeline
+from returns.result import Failure, Result, Success
+from returns.primitives.exceptions import UnwrapFailedError
+
+__all__ = (  # noqa: Z410
+    'compose',
+    'safe',
+    'pipeline',
+    'Failure',
+    'Result',
+    'Success',
+    'UnwrapFailedError',
+)

returns/functions.py

@@ -56,9 +56,29 @@ def compose(first, second):
     """
     Allows function composition.
 
-    Works as: second . first
+    Works as: ``second . first``
     You can read it as "second after first".
 
     We can only compose functions with one argument and one return.
     """
     return lambda argument: second(first(argument))
+
+
+def raise_exception(exception):
+    """
+    Helper function to raise exceptions as a function.
+
+    That's how it can be used:
+
+    .. code:: python
+
+      from returns.functions import raise_exception
+
+      # Some operation result:
+      user: Failure[UserDoesNotExistError]
+      # Here we unwrap internal exception and raise it:
+      user.fix(raise_exception)
+
+    See: https://github.com/dry-python/returns/issues/56
+    """
+    raise exception

returns/functions.pyi

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 
-from typing import Callable, TypeVar
+from typing import Callable, NoReturn, TypeVar
 
 from returns.primitives.container import Container
 from returns.result import Result
@@ -39,3 +39,7 @@ def compose(
     second: Callable[[_SecondType], _ThirdType],
 ) -> Callable[[_FirstType], _ThirdType]:
     ...
+
+
+def raise_exception(exception: Exception) -> NoReturn:
+    ...

setup.cfg

@@ -25,6 +25,8 @@ max-methods = 8
 per-file-ignores =
   # Disable some pydocstyle checks for package:
   returns/**/*.py: D104
+  # Disable imports in `__init__.py`:
+  returns/__init__.py: F401, Z412
   # There are multiple assert's in tests:
   tests/**/test_*.py: S101
   # Disable some pydocstyle checks globally:

tests/test_functions/test_raise_exception.py

@@ -0,0 +1,35 @@
+# -*- coding: utf-8 -*-
+
+from typing import Type
+
+import pytest
+
+from returns.functions import raise_exception
+from returns.result import Failure, Success
+
+
+class _CustomException(Exception):
+    """Just for the test."""
+
+
+@pytest.mark.parametrize('exception_type', [
+    TypeError,
+    ValueError,
+    _CustomException,
+])
+def test_raise_regular_exception(exception_type: Type[Exception]):
+    """Ensures that regular exception can be thrown."""
+    with pytest.raises(exception_type):
+        raise_exception(exception_type())
+
+
+def test_failure_can_be_fixed():
+    """Ensures that exceptions can work with Failures."""
+    failure = Failure(ValueError('Message'))
+    with pytest.raises(ValueError):
+        failure.fix(raise_exception)
+
+
+def test_success_is_not_touched():
+    """Ensures that exceptions can work with Success."""
+    assert Success(1).fix(raise_exception) == Success(1)