added python venv language

pre_commit/languages/python_venv.py

@@ -0,0 +1,73 @@
+from __future__ import unicode_literals
+
+import contextlib
+import os
+import sys
+
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import UNSET
+from pre_commit.envcontext import Var
+from pre_commit.languages import helpers
+from pre_commit.languages.python import get_default_version  # noqa: F401
+from pre_commit.languages.python import norm_version
+from pre_commit.util import clean_path_on_failure
+from pre_commit.util import cmd_output
+from pre_commit.xargs import xargs
+
+
+ENVIRONMENT_DIR = 'py_venv'
+
+
+def bin_dir(venv):
+    """On windows there's a different directory for the virtualenv"""
+    bin_part = 'Scripts' if os.name == 'nt' else 'bin'
+    return os.path.join(venv, bin_part)
+
+
+def get_env_patch(venv):
+    return (
+        ('PYTHONHOME', UNSET),
+        ('VIRTUAL_ENV', venv),
+        ('PATH', (bin_dir(venv), os.pathsep, Var('PATH'))),
+    )
+
+
+@contextlib.contextmanager
+def in_env(prefix, language_version):
+    envdir = prefix.path(
+        helpers.environment_dir(ENVIRONMENT_DIR, language_version),
+    )
+    with envcontext(get_env_patch(envdir)):
+        yield
+
+
+def healthy(prefix, language_version):
+    with in_env(prefix, language_version):
+        retcode, _, _ = cmd_output(
+            'python', '-c', 'import ctypes, datetime, io, os, ssl, weakref',
+            retcode=None,
+        )
+    return retcode == 0
+
+
+def install_environment(prefix, version, additional_dependencies):
+    additional_dependencies = tuple(additional_dependencies)
+    directory = helpers.environment_dir(ENVIRONMENT_DIR, version)
+
+    # Install a virtualenv
+    env_dir = prefix.path(directory)
+    with clean_path_on_failure(env_dir):
+        if version != 'default':
+            executable = norm_version(version)
+        else:
+            executable = os.path.realpath(sys.executable)
+        cmd_output(executable, '-m', 'venv', env_dir, cwd='/')
+        with in_env(prefix, version):
+            helpers.run_setup_cmd(
+                prefix, ('pip', 'install', '.') + additional_dependencies,
+            )
+
+
+def run_hook(prefix, hook, file_args):
+    with in_env(prefix, hook['language_version']):
+        return xargs(helpers.to_cmd(hook), file_args)