Use black to format code.

Closes #114

.flake8

@@ -0,0 +1,6 @@
+[flake8]
+# Ignore black styles.
+ignore = E501, W503
+# Imports
+import-order-style = google
+application-import-names = nox,tests

nox.py

@@ -17,55 +17,50 @@
 import nox
 
 
-ON_APPVEYOR = os.environ.get('APPVEYOR') == 'True'
+ON_APPVEYOR = os.environ.get("APPVEYOR") == "True"
 
 
-@nox.session(python=['3.5', '3.6', '3.7'])
+@nox.session(python=["3.5", "3.6", "3.7"])
 def tests(session):
-    session.install('-r', 'requirements-test.txt')
-    session.install('-e', '.[tox_to_nox]')
-    tests = session.posargs or ['tests/']
+    session.install("-r", "requirements-test.txt")
+    session.install("-e", ".[tox_to_nox]")
+    tests = session.posargs or ["tests/"]
     session.run(
-        'py.test', '--cov=nox', '--cov-config', '.coveragerc',
-        '--cov-report=', *tests)
-    session.notify('cover')
+        "py.test", "--cov=nox", "--cov-config", ".coveragerc", "--cov-report=", *tests
+    )
+    session.notify("cover")
 
 
 @nox.session
 def cover(session):
-    session.install('coverage')
+    session.install("coverage")
     if ON_APPVEYOR:
-        fail_under = '--fail-under=99'
+        fail_under = "--fail-under=99"
     else:
-        fail_under = '--fail-under=100'
-    session.run(
-        'coverage',
-        'report',
-        fail_under,
-        '--show-missing',
-    )
-    session.run('coverage', 'erase')
+        fail_under = "--fail-under=100"
+    session.run("coverage", "report", fail_under, "--show-missing")
+    session.run("coverage", "erase")
 
 
-@nox.session
+@nox.session(python="3.6")
+def blacken(session):
+    session.install("black")
+    session.run("black", "nox", "tests", "nox.py", "setup.py")
+
+
+@nox.session(python="3.6")
 def lint(session):
-    session.install('flake8', 'flake8-import-order')
-    session.run(
-        'flake8',
-        '--import-order-style=google',
-        '--application-import-names=nox,tests',
-        'nox', 'tests')
+    session.install("flake8", "flake8-import-order", "black")
+    session.run("black", "--check", "nox", "tests", "nox.py", "setup.py")
+    session.run("flake8", "nox", "tests")
 
 
-@nox.session(python='3.6')
+@nox.session(python="3.6")
 def docs(session):
-    session.run('rm', '-rf', 'docs/_build')
-    session.install('-r', 'requirements-test.txt')
-    session.install('.')
-    session.cd('docs')
+    session.run("rm", "-rf", "docs/_build")
+    session.install("-r", "requirements-test.txt")
+    session.install(".")
+    session.cd("docs")
     session.run(
-        'sphinx-build',
-        '-b', 'html',
-        '-W',
-        '-d', '_build/doctrees',
-        '.', '_build/html')
+        "sphinx-build", "-b", "html", "-W", "-d", "_build/doctrees", ".", "_build/html"
+    )

nox/__init__.py

@@ -15,4 +15,4 @@
 from nox._parametrize import parametrize_decorator as parametrize
 from nox.registry import session_decorator as session
 
-__all__ = ['parametrize', 'session']
+__all__ = ["parametrize", "session"]

nox/_parametrize.py

@@ -36,8 +36,7 @@ def parametrize_decorator(arg_names, arg_values_list):
 
     # Allow args to be specified as any of 'arg', 'arg,arg2' or ('arg', 'arg2')
     if not isinstance(arg_names, (list, tuple)):
-        arg_names = list(
-            filter(None, [arg.strip() for arg in arg_names.split(',')]))
+        arg_names = list(filter(None, [arg.strip() for arg in arg_names.split(",")]))
 
     # If there's only one arg_name, arg_values_list should be a single item
     # or list. Transform it so it'll work with the combine step.
@@ -56,10 +55,9 @@ def parametrize_decorator(arg_names, arg_values_list):
         call_specs.append(call_spec)
 
     def inner(f):
-        previous_call_specs = getattr(f, 'parametrize', None)
-        new_call_specs = update_call_specs(
-            previous_call_specs, call_specs)
-        setattr(f, 'parametrize', new_call_specs)
+        previous_call_specs = getattr(f, "parametrize", None)
+        new_call_specs = update_call_specs(previous_call_specs, call_specs)
+        setattr(f, "parametrize", new_call_specs)
         return f
 
     return inner
@@ -79,10 +77,8 @@ def update_call_specs(call_specs, new_specs):
 
 
 def generate_session_signature(func, call_spec):
-    args = [
-        '{}={}'.format(k, repr(call_spec[k]))
-        for k in sorted(call_spec.keys())]
-    return '({})'.format(', '.join(args))
+    args = ["{}={}".format(k, repr(call_spec[k])) for k in sorted(call_spec.keys())]
+    return "({})".format(", ".join(args))
 
 
 def generate_calls(func, call_specs):
@@ -94,6 +90,7 @@ def make_call_wrapper(call_spec):
             def call_wrapper(*args, **kwargs):
                 kwargs.update(call_spec)
                 return func(*args, **kwargs)
+
             return call_wrapper
 
         call = make_call_wrapper(call_spec)

nox/command.py

@@ -23,6 +23,7 @@
 
 class CommandFailed(Exception):
     """Raised when an executed command returns a non-success status code."""
+
     def __init__(self, reason=None):
         super(CommandFailed, self).__init__(reason)
         self.reason = reason
@@ -43,8 +44,8 @@ def which(program, path):
     if full_path:
         return full_path.strpath
 
-    logger.error('Program {} not found.'.format(program))
-    raise CommandFailed('Program {} not found'.format(program))
+    logger.error("Program {} not found.".format(program))
+    raise CommandFailed("Program {} not found".format(program))
 
 
 def _clean_env(env):
@@ -55,27 +56,24 @@ def _clean_env(env):
     clean_env = {}
 
     # Ensure systemroot is passed down, otherwise Windows will explode.
-    clean_env['SYSTEMROOT'] = os.environ.get('SYSTEMROOT', '')
+    clean_env["SYSTEMROOT"] = os.environ.get("SYSTEMROOT", "")
 
     for key, value in env.items():
-        key = key.decode('utf-8') if isinstance(key, bytes) else key
-        value = (
-            value.decode('utf-8') if isinstance(value, bytes) else value)
+        key = key.decode("utf-8") if isinstance(key, bytes) else key
+        value = value.decode("utf-8") if isinstance(value, bytes) else value
         clean_env[key] = value
 
     return clean_env
 
 
-def run(args, *, env=None, silent=False, path=None,
-        success_codes=None, log=True):
+def run(args, *, env=None, silent=False, path=None, success_codes=None, log=True):
     """Run a command-line program."""
 
     if success_codes is None:
         success_codes = [0]
 
     cmd, args = args[0], args[1:]
-    full_cmd = '{} {}'.format(
-        cmd, ' '.join(args))
+    full_cmd = "{} {}".format(cmd, " ".join(args))
 
     cmd_path = which(cmd, path)
 
@@ -85,22 +83,22 @@ def run(args, *, env=None, silent=False, path=None,
     env = _clean_env(env)
 
     try:
-        return_code, output = popen(
-            [cmd_path] + list(args),
-            silent=silent,
-            env=env)
+        return_code, output = popen([cmd_path] + list(args), silent=silent, env=env)
 
         if return_code not in success_codes:
-            logger.error('Command {} failed with exit code {}{}'.format(
-                full_cmd, return_code, ':' if silent else ''))
+            logger.error(
+                "Command {} failed with exit code {}{}".format(
+                    full_cmd, return_code, ":" if silent else ""
+                )
+            )
 
             if silent:
                 sys.stderr.write(output)
 
-            raise CommandFailed('Returned code {}'.format(return_code))
+            raise CommandFailed("Returned code {}".format(return_code))
 
         return output if silent else True
 
     except KeyboardInterrupt:
-        logger.error('Interrupted...')
+        logger.error("Interrupted...")
         raise

nox/logger.py

@@ -32,7 +32,7 @@ def success(self, msg, *args, **kwargs):
 
 
 logging.setLoggerClass(LoggerWithSuccess)
-logger = logging.getLogger('nox')
+logger = logging.getLogger("nox")
 logger.setLevel(logging.DEBUG)
 
 
@@ -52,18 +52,18 @@ def setup_logging(color):  # pragma: no cover
             "%(cyan)s%(name)s > %(log_color)s%(message)s",
             reset=True,
             log_colors={
-                'DEBUG': 'cyan',
-                'INFO': 'blue',
-                'WARNING': 'yellow',
-                'ERROR': 'red',
-                'CRITICAL': 'red,bg_white',
-                'SUCCESS': 'green'
-            }
+                "DEBUG": "cyan",
+                "INFO": "blue",
+                "WARNING": "yellow",
+                "ERROR": "red",
+                "CRITICAL": "red,bg_white",
+                "SUCCESS": "green",
+            },
         )
 
         handler.setFormatter(formatter)
 
     root_logger.addHandler(handler)
 
     # Silence noisy loggers
-    logging.getLogger('sh').setLevel(logging.WARNING)
+    logging.getLogger("sh").setLevel(logging.WARNING)

nox/main.py

@@ -42,55 +42,74 @@ def __init__(self, args):
         self.posargs = args.posargs
         self.report = args.report
 
-        if self.posargs and self.posargs[0] == '--':
+        if self.posargs and self.posargs[0] == "--":
             self.posargs.pop(0)
 
 
 def main():
-    parser = argparse.ArgumentParser(
-        description='nox is a Python automation toolkit.')
+    parser = argparse.ArgumentParser(description="nox is a Python automation toolkit.")
     parser.add_argument(
-        '-f', '--noxfile', default='nox.py',
-        help='Location of the Python file containing nox sessions.')
+        "-f",
+        "--noxfile",
+        default="nox.py",
+        help="Location of the Python file containing nox sessions.",
+    )
     parser.add_argument(
-        '-l', '--list-sessions', action='store_true',
-        help='List all available sessions and exit.')
+        "-l",
+        "--list-sessions",
+        action="store_true",
+        help="List all available sessions and exit.",
+    )
     parser.add_argument(
-        '--envdir', default='.nox',
-        help='Directory where nox will store virtualenvs.')
+        "--envdir", default=".nox", help="Directory where nox will store virtualenvs."
+    )
     parser.add_argument(
-        '-s', '-e', '--sessions', nargs='*',
-        help='Which sessions to run, by default, all sessions will run.')
+        "-s",
+        "-e",
+        "--sessions",
+        nargs="*",
+        help="Which sessions to run, by default, all sessions will run.",
+    )
     parser.add_argument(
-        '-k', '--keywords',
-        help='Only run sessions that match the given expression.')
+        "-k", "--keywords", help="Only run sessions that match the given expression."
+    )
     parser.add_argument(
-        '-r', '--reuse-existing-virtualenvs', action='store_true',
-        help='Re-use existing virtualenvs instead of recreating them.')
+        "-r",
+        "--reuse-existing-virtualenvs",
+        action="store_true",
+        help="Re-use existing virtualenvs instead of recreating them.",
+    )
     parser.add_argument(
-        '--stop-on-first-error', action='store_true',
-        help='Stop after the first error.')
+        "--stop-on-first-error", action="store_true", help="Stop after the first error."
+    )
     parser.add_argument(
-        '--report', default=None,
-        help='Output a report of all sessions.')
+        "--report", default=None, help="Output a report of all sessions."
+    )
     parser.add_argument(
-        '--nocolor', default=not sys.stderr.isatty(), action='store_true',
-        help='Disable all color output.')
+        "--nocolor",
+        default=not sys.stderr.isatty(),
+        action="store_true",
+        help="Disable all color output.",
+    )
     parser.add_argument(
-        '--forcecolor', default=False, action='store_true',
-        help=('Force color output, even if stdout is not an interactive '
-              'terminal.'))
+        "--forcecolor",
+        default=False,
+        action="store_true",
+        help=("Force color output, even if stdout is not an interactive " "terminal."),
+    )
     parser.add_argument(
-        'posargs', nargs=argparse.REMAINDER,
-        help='Arguments that are passed through to the sessions.')
+        "posargs",
+        nargs=argparse.REMAINDER,
+        help="Arguments that are passed through to the sessions.",
+    )
     parser.add_argument(
-        '--version', action='store_true',
-        help='Output the nox version and exit.')
+        "--version", action="store_true", help="Output the nox version and exit."
+    )
 
     args = parser.parse_args()
 
     if args.version:
-        dist = pkg_resources.get_distribution('nox')
+        dist = pkg_resources.get_distribution("nox")
         print(dist.version, file=sys.stderr)
         return