Added mypy for static type checking

Author: sybrenstuvel

.gitignore

@@ -12,6 +12,7 @@
 .coverage
 .coverage.*
 .cache/
+.mypy_cache/
 .pytest_cache/
 __pycache__/
 

Pipfile

@@ -13,7 +13,8 @@ Sphinx = "*"
 coveralls = "*"
 pytest = "*"
 pytest-cov = "*"
-pathlib2 = {version = "*", markers="python_version < '3.6'"}
+pathlib2 = {version = "*",markers = "python_version < '3.6'"}
+mypy = "*"
 
 [requires]
 python_version = "3.7"

Pipfile.lock

@@ -21,9 +21,11 @@
 
 import abc
 import sys
+import typing
 from optparse import OptionParser
 
 import rsa
+import rsa.key
 import rsa.pkcs1
 
 HASH_METHODS = sorted(rsa.pkcs1.HASH_METHODS.keys())
@@ -84,14 +86,12 @@ def keygen():
         sys.stdout.buffer.write(data)
 
 
-class CryptoOperation(object):
+class CryptoOperation(metaclass=abc.ABCMeta):
     """CLI callable that operates with input, output, and a key."""
 
-    __metaclass__ = abc.ABCMeta
-
     keyname = 'public'  # or 'private'
     usage = 'usage: %%prog [options] %(keyname)s_key'
-    description = None
+    description = ''
     operation = 'decrypt'
     operation_past = 'decrypted'
     operation_progressive = 'decrypting'
@@ -102,7 +102,7 @@ class CryptoOperation(object):
     expected_cli_args = 1
     has_output = True
 
-    key_class = rsa.PublicKey
+    key_class = rsa.PublicKey  # type: typing.Type[rsa.key.AbstractKey]
 
     def __init__(self):
         self.usage = self.usage % self.__class__.__dict__

rsa/cli.py

@@ -3,3 +3,16 @@ universal = 1
 
 [metadata]
 license_file = LICENSE
+
+[flake8]
+max-line-length = 100
+
+[pep8]
+max-line-length = 100
+
+[mypy]
+python_version = 3.7
+warn_unused_ignores = True
+ignore_missing_imports = True
+follow_imports = skip
+incremental = True

setup.cfg

@@ -4,41 +4,37 @@
 
 from __future__ import print_function
 
-import unittest
-import sys
 import functools
-from contextlib import contextmanager
-
+import io
 import os
-from io import StringIO, BytesIO
+import sys
+import typing
+import unittest
+from contextlib import contextmanager, redirect_stdout, redirect_stderr
 
 import rsa
 import rsa.cli
 import rsa.util
 
 
-def make_buffer() -> StringIO:
-    buf = StringIO()
-    buf.buffer = BytesIO()
-    return buf
+@contextmanager
+def captured_output() -> typing.Generator:
+    """Captures output to stdout and stderr"""
 
+    # According to mypy, we're not supposed to change buf_out.buffer.
+    # However, this is just a test, and it works, hence the 'type: ignore'.
+    buf_out = io.StringIO()
+    buf_out.buffer = io.BytesIO()  # type: ignore
 
-def get_bytes_out(out: StringIO) -> bytes:
-    # Python 3.x writes 'bytes' to stdout.buffer
-    return out.buffer.getvalue()
+    buf_err = io.StringIO()
+    buf_err.buffer = io.BytesIO()  # type: ignore
 
+    with redirect_stdout(buf_out), redirect_stderr(buf_err):
+        yield buf_out, buf_err
 
-@contextmanager
-def captured_output():
-    """Captures output to stdout and stderr"""
 
-    new_out, new_err = make_buffer(), make_buffer()
-    old_out, old_err = sys.stdout, sys.stderr
-    try:
-        sys.stdout, sys.stderr = new_out, new_err
-        yield new_out, new_err
-    finally:
-        sys.stdout, sys.stderr = old_out, old_err
+def get_bytes_out(buf) -> bytes:
+    return buf.buffer.getvalue()
 
 
 @contextmanager

tests/test_cli.py

@@ -0,0 +1,27 @@
+import pathlib
+import unittest
+
+import mypy.api
+
+test_modules = ['rsa', 'tests']
+
+
+class MypyRunnerTest(unittest.TestCase):
+    def test_run_mypy(self):
+        proj_root = pathlib.Path(__file__).parent.parent
+        args = ['--incremental', '--ignore-missing-imports'] + [str(proj_root / dirname) for dirname
+                                                                in test_modules]
+
+        result = mypy.api.run(args)
+
+        stdout, stderr, status = result
+
+        messages = []
+        if stderr:
+            messages.append(stderr)
+        if stdout:
+            messages.append(stdout)
+        if status:
+            messages.append('Mypy failed with status %d' % status)
+        if messages:
+            self.fail('\n'.join(['Mypy errors:'] + messages))

tests/test_mypy.py

@@ -15,6 +15,3 @@ commands=
 commands=
     pipenv install --dev --ignore-pipfile
     pipenv run py.test --doctest-modules rsa tests
-
-[pep8]
-max-line-length = 100