Source code for _pytest.main

"""Core implementation of the testing process: init, session, runtest loop."""
import argparse
import fnmatch
import functools
import importlib
import os
import sys
from typing import Callable
from typing import Dict
from typing import FrozenSet
from typing import Iterator
from typing import List
from typing import Optional
from typing import Sequence
from typing import Set
from typing import Tuple
from typing import Union

import attr
import py

import _pytest._code
from _pytest import nodes
from _pytest.compat import final
from _pytest.compat import overload
from _pytest.compat import TYPE_CHECKING
from _pytest.config import Config
from _pytest.config import directory_arg
from _pytest.config import ExitCode
from _pytest.config import hookimpl
from _pytest.config import PytestPluginManager
from _pytest.config import UsageError
from _pytest.config.argparsing import Parser
from _pytest.fixtures import FixtureManager
from _pytest.outcomes import exit
from _pytest.pathlib import absolutepath
from _pytest.pathlib import bestrelpath
from _pytest.pathlib import Path
from _pytest.pathlib import visit
from _pytest.reports import CollectReport
from _pytest.reports import TestReport
from _pytest.runner import collect_one_node
from _pytest.runner import SetupState


if TYPE_CHECKING:
    from typing import Type
    from typing_extensions import Literal


def pytest_addoption(parser: Parser) -> None:
    parser.addini(
        "norecursedirs",
        "directory patterns to avoid for recursion",
        type="args",
        default=[".*", "build", "dist", "CVS", "_darcs", "{arch}", "*.egg", "venv"],
    )
    parser.addini(
        "testpaths",
        "directories to search for tests when no files or directories are given in the "
        "command line.",
        type="args",
        default=[],
    )
    group = parser.getgroup("general", "running and selection options")
    group._addoption(
        "-x",
        "--exitfirst",
        action="store_const",
        dest="maxfail",
        const=1,
        help="exit instantly on first error or failed test.",
    )
    group = parser.getgroup("pytest-warnings")
    group.addoption(
        "-W",
        "--pythonwarnings",
        action="append",
        help="set which warnings to report, see -W option of python itself.",
    )
    parser.addini(
        "filterwarnings",
        type="linelist",
        help="Each line specifies a pattern for "
        "warnings.filterwarnings. "
        "Processed after -W/--pythonwarnings.",
    )
    group._addoption(
        "--maxfail",
        metavar="num",
        action="store",
        type=int,
        dest="maxfail",
        default=0,
        help="exit after first num failures or errors.",
    )
    group._addoption(
        "--strict-config",
        action="store_true",
        help="any warnings encountered while parsing the `pytest` section of the configuration file raise errors.",
    )
    group._addoption(
        "--strict-markers",
        "--strict",
        action="store_true",
        help="markers not registered in the `markers` section of the configuration file raise errors.",
    )
    group._addoption(
        "-c",
        metavar="file",
        type=str,
        dest="inifilename",
        help="load configuration from `file` instead of trying to locate one of the implicit "
        "configuration files.",
    )
    group._addoption(
        "--continue-on-collection-errors",
        action="store_true",
        default=False,
        dest="continue_on_collection_errors",
        help="Force test execution even if collection errors occur.",
    )
    group._addoption(
        "--rootdir",
        action="store",
        dest="rootdir",
        help="Define root directory for tests. Can be relative path: 'root_dir', './root_dir', "
        "'root_dir/another_dir/'; absolute path: '/home/user/root_dir'; path with variables: "
        "'$HOME/root_dir'.",
    )

    group = parser.getgroup("collect", "collection")
    group.addoption(
        "--collectonly",
        "--collect-only",
        "--co",
        action="store_true",
        help="only collect tests, don't execute them.",
    )
    group.addoption(
        "--pyargs",
        action="store_true",
        help="try to interpret all arguments as python packages.",
    )
    group.addoption(
        "--ignore",
        action="append",
        metavar="path",
        help="ignore path during collection (multi-allowed).",
    )
    group.addoption(
        "--ignore-glob",
        action="append",
        metavar="path",
        help="ignore path pattern during collection (multi-allowed).",
    )
    group.addoption(
        "--deselect",
        action="append",
        metavar="nodeid_prefix",
        help="deselect item (via node id prefix) during collection (multi-allowed).",
    )
    group.addoption(
        "--confcutdir",
        dest="confcutdir",
        default=None,
        metavar="dir",
        type=functools.partial(directory_arg, optname="--confcutdir"),
        help="only load conftest.py's relative to specified dir.",
    )
    group.addoption(
        "--noconftest",
        action="store_true",
        dest="noconftest",
        default=False,
        help="Don't load any conftest.py files.",
    )
    group.addoption(
        "--keepduplicates",
        "--keep-duplicates",
        action="store_true",
        dest="keepduplicates",
        default=False,
        help="Keep duplicate tests.",
    )
    group.addoption(
        "--collect-in-virtualenv",
        action="store_true",
        dest="collect_in_virtualenv",
        default=False,
        help="Don't ignore tests in a local virtualenv directory",
    )
    group.addoption(
        "--import-mode",
        default="prepend",
        choices=["prepend", "append", "importlib"],
        dest="importmode",
        help="prepend/append to sys.path when importing test modules and conftest files, "
        "default is to prepend.",
    )

    group = parser.getgroup("debugconfig", "test session debugging and configuration")
    group.addoption(
        "--basetemp",
        dest="basetemp",
        default=None,
        type=validate_basetemp,
        metavar="dir",
        help=(
            "base temporary directory for this test run."
            "(warning: this directory is removed if it exists)"
        ),
    )


def validate_basetemp(path: str) -> str:
    # GH 7119
    msg = "basetemp must not be empty, the current working directory or any parent directory of it"

    # empty path
    if not path:
        raise argparse.ArgumentTypeError(msg)

    def is_ancestor(base: Path, query: Path) -> bool:
        """Return whether query is an ancestor of base."""
        if base == query:
            return True
        for parent in base.parents:
            if parent == query:
                return True
        return False

    # check if path is an ancestor of cwd
    if is_ancestor(Path.cwd(), Path(path).absolute()):
        raise argparse.ArgumentTypeError(msg)

    # check symlinks for ancestors
    if is_ancestor(Path.cwd().resolve(), Path(path).resolve()):
        raise argparse.ArgumentTypeError(msg)

    return path


def wrap_session(
    config: Config, doit: Callable[[Config, "Session"], Optional[Union[int, ExitCode]]]
) -> Union[int, ExitCode]:
    """Skeleton command line program."""
    session = Session.from_config(config)
    session.exitstatus = ExitCode.OK
    initstate = 0
    try:
        try:
            config._do_configure()
            initstate = 1
            config.hook.pytest_sessionstart(session=session)
            initstate = 2
            session.exitstatus = doit(config, session) or 0
        except UsageError:
            session.exitstatus = ExitCode.USAGE_ERROR
            raise
        except Failed:
            session.exitstatus = ExitCode.TESTS_FAILED
        except (KeyboardInterrupt, exit.Exception):
            excinfo = _pytest._code.ExceptionInfo.from_current()
            exitstatus = ExitCode.INTERRUPTED  # type: Union[int, ExitCode]
            if isinstance(excinfo.value, exit.Exception):
                if excinfo.value.returncode is not None:
                    exitstatus = excinfo.value.returncode
                if initstate < 2:
                    sys.stderr.write(
                        "{}: {}\n".format(excinfo.typename, excinfo.value.msg)
                    )
            config.hook.pytest_keyboard_interrupt(excinfo=excinfo)
            session.exitstatus = exitstatus
        except BaseException:
            session.exitstatus = ExitCode.INTERNAL_ERROR
            excinfo = _pytest._code.ExceptionInfo.from_current()
            try:
                config.notify_exception(excinfo, config.option)
            except exit.Exception as exc:
                if exc.returncode is not None:
                    session.exitstatus = exc.returncode
                sys.stderr.write("{}: {}\n".format(type(exc).__name__, exc))
            else:
                if isinstance(excinfo.value, SystemExit):
                    sys.stderr.write("mainloop: caught unexpected SystemExit!\n")

    finally:
        # Explicitly break reference cycle.
        excinfo = None  # type: ignore
        session.startdir.chdir()
        if initstate >= 2:
            try:
                config.hook.pytest_sessionfinish(
                    session=session, exitstatus=session.exitstatus
                )
            except exit.Exception as exc:
                if exc.returncode is not None:
                    session.exitstatus = exc.returncode
                sys.stderr.write("{}: {}\n".format(type(exc).__name__, exc))
        config._ensure_unconfigure()
    return session.exitstatus


def pytest_cmdline_main(config: Config) -> Union[int, ExitCode]:
    return wrap_session(config, _main)


def _main(config: Config, session: "Session") -> Optional[Union[int, ExitCode]]:
    """Default command line protocol for initialization, session,
    running tests and reporting."""
    config.hook.pytest_collection(session=session)
    config.hook.pytest_runtestloop(session=session)

    if session.testsfailed:
        return ExitCode.TESTS_FAILED
    elif session.testscollected == 0:
        return ExitCode.NO_TESTS_COLLECTED
    return None


def pytest_collection(session: "Session") -> None:
    session.perform_collect()


def pytest_runtestloop(session: "Session") -> bool:
    if session.testsfailed and not session.config.option.continue_on_collection_errors:
        raise session.Interrupted(
            "%d error%s during collection"
            % (session.testsfailed, "s" if session.testsfailed != 1 else "")
        )

    if session.config.option.collectonly:
        return True

    for i, item in enumerate(session.items):
        nextitem = session.items[i + 1] if i + 1 < len(session.items) else None
        item.config.hook.pytest_runtest_protocol(item=item, nextitem=nextitem)
        if session.shouldfail:
            raise session.Failed(session.shouldfail)
        if session.shouldstop:
            raise session.Interrupted(session.shouldstop)
    return True


def _in_venv(path: py.path.local) -> bool:
    """Attempt to detect if ``path`` is the root of a Virtual Environment by
    checking for the existence of the appropriate activate script."""
    bindir = path.join("Scripts" if sys.platform.startswith("win") else "bin")
    if not bindir.isdir():
        return False
    activates = (
        "activate",
        "activate.csh",
        "activate.fish",
        "Activate",
        "Activate.bat",
        "Activate.ps1",
    )
    return any([fname.basename in activates for fname in bindir.listdir()])


def pytest_ignore_collect(path: py.path.local, config: Config) -> Optional[bool]:
    ignore_paths = config._getconftest_pathlist("collect_ignore", path=path.dirpath())
    ignore_paths = ignore_paths or []
    excludeopt = config.getoption("ignore")
    if excludeopt:
        ignore_paths.extend([py.path.local(x) for x in excludeopt])

    if py.path.local(path) in ignore_paths:
        return True

    ignore_globs = config._getconftest_pathlist(
        "collect_ignore_glob", path=path.dirpath()
    )
    ignore_globs = ignore_globs or []
    excludeglobopt = config.getoption("ignore_glob")
    if excludeglobopt:
        ignore_globs.extend([py.path.local(x) for x in excludeglobopt])

    if any(fnmatch.fnmatch(str(path), str(glob)) for glob in ignore_globs):
        return True

    allow_in_venv = config.getoption("collect_in_virtualenv")
    if not allow_in_venv and _in_venv(path):
        return True
    return None


def pytest_collection_modifyitems(items: List[nodes.Item], config: Config) -> None:
    deselect_prefixes = tuple(config.getoption("deselect") or [])
    if not deselect_prefixes:
        return

    remaining = []
    deselected = []
    for colitem in items:
        if colitem.nodeid.startswith(deselect_prefixes):
            deselected.append(colitem)
        else:
            remaining.append(colitem)

    if deselected:
        config.hook.pytest_deselected(items=deselected)
        items[:] = remaining


class FSHookProxy:
    def __init__(self, pm: PytestPluginManager, remove_mods) -> None:
        self.pm = pm
        self.remove_mods = remove_mods

    def __getattr__(self, name: str):
        x = self.pm.subset_hook_caller(name, remove_plugins=self.remove_mods)
        self.__dict__[name] = x
        return x


class Interrupted(KeyboardInterrupt):
    """Signals that the test run was interrupted."""

    __module__ = "builtins"  # For py3.


class Failed(Exception):
    """Signals a stop as failed test run."""


@attr.s
class _bestrelpath_cache(Dict[Path, str]):
    path = attr.ib(type=Path)

    def __missing__(self, path: Path) -> str:
        r = bestrelpath(self.path, path)
        self[path] = r
        return r


[docs]@final class Session(nodes.FSCollector): Interrupted = Interrupted Failed = Failed # Set on the session by runner.pytest_sessionstart. _setupstate = None # type: SetupState # Set on the session by fixtures.pytest_sessionstart. _fixturemanager = None # type: FixtureManager exitstatus = None # type: Union[int, ExitCode] def __init__(self, config: Config) -> None: super().__init__( config.rootdir, parent=None, config=config, session=self, nodeid="" ) self.testsfailed = 0 self.testscollected = 0 self.shouldstop = False # type: Union[bool, str] self.shouldfail = False # type: Union[bool, str] self.trace = config.trace.root.get("collection") self.startdir = config.invocation_dir self._initialpaths = frozenset() # type: FrozenSet[py.path.local] self._bestrelpathcache = _bestrelpath_cache( config.rootpath ) # type: Dict[Path, str] self.config.pluginmanager.register(self, name="session") @classmethod def from_config(cls, config: Config) -> "Session": session = cls._create(config) # type: Session return session def __repr__(self) -> str: return "<%s %s exitstatus=%r testsfailed=%d testscollected=%d>" % ( self.__class__.__name__, self.name, getattr(self, "exitstatus", "<UNSET>"), self.testsfailed, self.testscollected, ) def _node_location_to_relpath(self, node_path: Path) -> str: # bestrelpath is a quite slow function. return self._bestrelpathcache[node_path] @hookimpl(tryfirst=True) def pytest_collectstart(self) -> None: if self.shouldfail: raise self.Failed(self.shouldfail) if self.shouldstop: raise self.Interrupted(self.shouldstop) @hookimpl(tryfirst=True) def pytest_runtest_logreport( self, report: Union[TestReport, CollectReport] ) -> None: if report.failed and not hasattr(report, "wasxfail"): self.testsfailed += 1 maxfail = self.config.getvalue("maxfail") if maxfail and self.testsfailed >= maxfail: self.shouldfail = "stopping after %d failures" % (self.testsfailed) pytest_collectreport = pytest_runtest_logreport def isinitpath(self, path: py.path.local) -> bool: return path in self._initialpaths def gethookproxy(self, fspath: py.path.local): # Check if we have the common case of running # hooks with all conftest.py files. pm = self.config.pluginmanager my_conftestmodules = pm._getconftestmodules( fspath, self.config.getoption("importmode") ) remove_mods = pm._conftest_plugins.difference(my_conftestmodules) if remove_mods: # One or more conftests are not in use at this fspath. proxy = FSHookProxy(pm, remove_mods) else: # All plugins are active for this fspath. proxy = self.config.hook return proxy def _recurse(self, direntry: "os.DirEntry[str]") -> bool: if direntry.name == "__pycache__": return False path = py.path.local(direntry.path) ihook = self.gethookproxy(path.dirpath()) if ihook.pytest_ignore_collect(path=path, config=self.config): return False norecursepatterns = self.config.getini("norecursedirs") if any(path.check(fnmatch=pat) for pat in norecursepatterns): return False return True def _collectfile( self, path: py.path.local, handle_dupes: bool = True ) -> Sequence[nodes.Collector]: assert ( path.isfile() ), "{!r} is not a file (isdir={!r}, exists={!r}, islink={!r})".format( path, path.isdir(), path.exists(), path.islink() ) ihook = self.gethookproxy(path) if not self.isinitpath(path): if ihook.pytest_ignore_collect(path=path, config=self.config): return () if handle_dupes: keepduplicates = self.config.getoption("keepduplicates") if not keepduplicates: duplicate_paths = self.config.pluginmanager._duplicatepaths if path in duplicate_paths: return () else: duplicate_paths.add(path) return ihook.pytest_collect_file(path=path, parent=self) # type: ignore[no-any-return] @overload def perform_collect( self, args: Optional[Sequence[str]] = ..., genitems: "Literal[True]" = ... ) -> Sequence[nodes.Item]: ... @overload # noqa: F811 def perform_collect( # noqa: F811 self, args: Optional[Sequence[str]] = ..., genitems: bool = ... ) -> Sequence[Union[nodes.Item, nodes.Collector]]: ...
[docs] def perform_collect( # noqa: F811 self, args: Optional[Sequence[str]] = None, genitems: bool = True ) -> Sequence[Union[nodes.Item, nodes.Collector]]: """Perform the collection phase for this session. This is called by the default :func:`pytest_collection <_pytest.hookspec.pytest_collection>` hook implementation; see the documentation of this hook for more details. For testing purposes, it may also be called directly on a fresh ``Session``. This function normally recursively expands any collectors collected from the session to their items, and only items are returned. For testing purposes, this may be suppressed by passing ``genitems=False``, in which case the return value contains these collectors unexpanded, and ``session.items`` is empty. """ if args is None: args = self.config.args self.trace("perform_collect", self, args) self.trace.root.indent += 1 self._notfound = [] # type: List[Tuple[str, Sequence[nodes.Collector]]] self._initial_parts = [] # type: List[Tuple[py.path.local, List[str]]] self.items = [] # type: List[nodes.Item] hook = self.config.hook items = self.items # type: Sequence[Union[nodes.Item, nodes.Collector]] try: initialpaths = [] # type: List[py.path.local] for arg in args: fspath, parts = resolve_collection_argument( self.config.invocation_params.dir, arg, as_pypath=self.config.option.pyargs, ) self._initial_parts.append((fspath, parts)) initialpaths.append(fspath) self._initialpaths = frozenset(initialpaths) rep = collect_one_node(self) self.ihook.pytest_collectreport(report=rep) self.trace.root.indent -= 1 if self._notfound: errors = [] for arg, cols in self._notfound: line = "(no name {!r} in any of {!r})".format(arg, cols) errors.append("not found: {}\n{}".format(arg, line)) raise UsageError(*errors) if not genitems: items = rep.result else: if rep.passed: for node in rep.result: self.items.extend(self.genitems(node)) self.config.pluginmanager.check_pending() hook.pytest_collection_modifyitems( session=self, config=self.config, items=items ) finally: hook.pytest_collection_finish(session=self) self.testscollected = len(items) return items
[docs] def collect(self) -> Iterator[Union[nodes.Item, nodes.Collector]]: from _pytest.python import Package # Keep track of any collected nodes in here, so we don't duplicate fixtures. node_cache1 = {} # type: Dict[py.path.local, Sequence[nodes.Collector]] node_cache2 = ( {} ) # type: Dict[Tuple[Type[nodes.Collector], py.path.local], nodes.Collector] # Keep track of any collected collectors in matchnodes paths, so they # are not collected more than once. matchnodes_cache = ( {} ) # type: Dict[Tuple[Type[nodes.Collector], str], CollectReport] # Dirnames of pkgs with dunder-init files. pkg_roots = {} # type: Dict[str, Package] for argpath, names in self._initial_parts: self.trace("processing argument", (argpath, names)) self.trace.root.indent += 1 # Start with a Session root, and delve to argpath item (dir or file) # and stack all Packages found on the way. # No point in finding packages when collecting doctests. if not self.config.getoption("doctestmodules", False): pm = self.config.pluginmanager for parent in reversed(argpath.parts()): if pm._confcutdir and pm._confcutdir.relto(parent): break if parent.isdir(): pkginit = parent.join("__init__.py") if pkginit.isfile() and pkginit not in node_cache1: col = self._collectfile(pkginit, handle_dupes=False) if col: if isinstance(col[0], Package): pkg_roots[str(parent)] = col[0] node_cache1[col[0].fspath] = [col[0]] # If it's a directory argument, recurse and look for any Subpackages. # Let the Package collector deal with subnodes, don't collect here. if argpath.check(dir=1): assert not names, "invalid arg {!r}".format((argpath, names)) seen_dirs = set() # type: Set[py.path.local] for direntry in visit(str(argpath), self._recurse): if not direntry.is_file(): continue path = py.path.local(direntry.path) dirpath = path.dirpath() if dirpath not in seen_dirs: # Collect packages first. seen_dirs.add(dirpath) pkginit = dirpath.join("__init__.py") if pkginit.exists(): for x in self._collectfile(pkginit): yield x if isinstance(x, Package): pkg_roots[str(dirpath)] = x if str(dirpath) in pkg_roots: # Do not collect packages here. continue for x in self._collectfile(path): key = (type(x), x.fspath) if key in node_cache2: yield node_cache2[key] else: node_cache2[key] = x yield x else: assert argpath.check(file=1) if argpath in node_cache1: col = node_cache1[argpath] else: collect_root = pkg_roots.get(argpath.dirname, self) col = collect_root._collectfile(argpath, handle_dupes=False) if col: node_cache1[argpath] = col matching = [] work = [ (col, names) ] # type: List[Tuple[Sequence[Union[nodes.Item, nodes.Collector]], Sequence[str]]] while work: self.trace("matchnodes", col, names) self.trace.root.indent += 1 matchnodes, matchnames = work.pop() for node in matchnodes: if not matchnames: matching.append(node) continue if not isinstance(node, nodes.Collector): continue key = (type(node), node.nodeid) if key in matchnodes_cache: rep = matchnodes_cache[key] else: rep = collect_one_node(node) matchnodes_cache[key] = rep if rep.passed: submatchnodes = [] for r in rep.result: # TODO: Remove parametrized workaround once collection structure contains # parametrization. if ( r.name == matchnames[0] or r.name.split("[")[0] == matchnames[0] ): submatchnodes.append(r) if submatchnodes: work.append((submatchnodes, matchnames[1:])) # XXX Accept IDs that don't have "()" for class instances. elif len(rep.result) == 1 and rep.result[0].name == "()": work.append((rep.result, matchnames)) else: # Report collection failures here to avoid failing to run some test # specified in the command line because the module could not be # imported (#134). node.ihook.pytest_collectreport(report=rep) self.trace("matchnodes finished -> ", len(matching), "nodes") self.trace.root.indent -= 1 if not matching: report_arg = "::".join((str(argpath), *names)) self._notfound.append((report_arg, col)) continue # If __init__.py was the only file requested, then the matched node will be # the corresponding Package, and the first yielded item will be the __init__ # Module itself, so just use that. If this special case isn't taken, then all # the files in the package will be yielded. if argpath.basename == "__init__.py": assert isinstance(matching[0], nodes.Collector) try: yield next(iter(matching[0].collect())) except StopIteration: # The package collects nothing with only an __init__.py # file in it, which gets ignored by the default # "python_files" option. pass continue yield from matching self.trace.root.indent -= 1
def genitems( self, node: Union[nodes.Item, nodes.Collector] ) -> Iterator[nodes.Item]: self.trace("genitems", node) if isinstance(node, nodes.Item): node.ihook.pytest_itemcollected(item=node) yield node else: assert isinstance(node, nodes.Collector) rep = collect_one_node(node) if rep.passed: for subnode in rep.result: yield from self.genitems(subnode) node.ihook.pytest_collectreport(report=rep)
def search_pypath(module_name: str) -> str: """Search sys.path for the given a dotted module name, and return its file system path.""" try: spec = importlib.util.find_spec(module_name) # AttributeError: looks like package module, but actually filename # ImportError: module does not exist # ValueError: not a module name except (AttributeError, ImportError, ValueError): return module_name if spec is None or spec.origin is None or spec.origin == "namespace": return module_name elif spec.submodule_search_locations: return os.path.dirname(spec.origin) else: return spec.origin def resolve_collection_argument( invocation_path: Path, arg: str, *, as_pypath: bool = False ) -> Tuple[py.path.local, List[str]]: """Parse path arguments optionally containing selection parts and return (fspath, names). Command-line arguments can point to files and/or directories, and optionally contain parts for specific tests selection, for example: "pkg/tests/test_foo.py::TestClass::test_foo" This function ensures the path exists, and returns a tuple: (py.path.path("/full/path/to/pkg/tests/test_foo.py"), ["TestClass", "test_foo"]) When as_pypath is True, expects that the command-line argument actually contains module paths instead of file-system paths: "pkg.tests.test_foo::TestClass::test_foo" In which case we search sys.path for a matching module, and then return the *path* to the found module. If the path doesn't exist, raise UsageError. If the path is a directory and selection parts are present, raise UsageError. """ strpath, *parts = str(arg).split("::") if as_pypath: strpath = search_pypath(strpath) fspath = invocation_path / strpath fspath = absolutepath(fspath) if not fspath.exists(): msg = ( "module or package not found: {arg} (missing __init__.py?)" if as_pypath else "file or directory not found: {arg}" ) raise UsageError(msg.format(arg=arg)) if parts and fspath.is_dir(): msg = ( "package argument cannot contain :: selection parts: {arg}" if as_pypath else "directory argument cannot contain :: selection parts: {arg}" ) raise UsageError(msg.format(arg=arg)) return py.path.local(str(fspath)), parts