_compat.py

# Copyright (c) 2009, Giampaolo Rodola'. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Module which provides compatibility with older Python versions.
This is more future-compatible rather than the opposite (prefer latest
Python 3 way of doing things).
"""

import collections
import contextlib
import errno
import functools
import os
import sys
import types


__all__ = [
    # constants
    "PY3",
    # builtins
    "long", "range", "super", "unicode", "basestring",
    # literals
    "u", "b",
    # collections module
    "lru_cache",
    # shutil module
    "which", "get_terminal_size",
    # contextlib module
    "redirect_stderr",
    # python 3 exceptions
    "FileNotFoundError", "PermissionError", "ProcessLookupError",
    "InterruptedError", "ChildProcessError", "FileExistsError"]


PY3 = sys.version_info[0] == 3
_SENTINEL = object()

if PY3:
    long = int
    xrange = range
    unicode = str
    basestring = str
    range = range

    def u(s):
        return s

    def b(s):
        return s.encode("latin-1")
else:
    long = long
    range = xrange
    unicode = unicode
    basestring = basestring

    def u(s):
        return unicode(s, "unicode_escape")

    def b(s):
        return s


# --- builtins


# Python 3 super().
# Taken from "future" package.
# Credit: Ryan Kelly
if PY3:
    super = super
else:
    _builtin_super = super

    def super(type_=_SENTINEL, type_or_obj=_SENTINEL, framedepth=1):
        """Like Python 3 builtin super(). If called without any arguments
        it attempts to infer them at runtime.
        """
        if type_ is _SENTINEL:
            f = sys._getframe(framedepth)
            try:
                # Get the function's first positional argument.
                type_or_obj = f.f_locals[f.f_code.co_varnames[0]]
            except (IndexError, KeyError):
                raise RuntimeError('super() used in a function with no args')
            try:
                # Get the MRO so we can crawl it.
                mro = type_or_obj.__mro__
            except (AttributeError, RuntimeError):
                try:
                    mro = type_or_obj.__class__.__mro__
                except AttributeError:
                    raise RuntimeError('super() used in a non-newstyle class')
            for type_ in mro:
                #  Find the class that owns the currently-executing method.
                for meth in type_.__dict__.values():
                    # Drill down through any wrappers to the underlying func.
                    # This handles e.g. classmethod() and staticmethod().
                    try:
                        while not isinstance(meth, types.FunctionType):
                            if isinstance(meth, property):
                                # Calling __get__ on the property will invoke
                                # user code which might throw exceptions or
                                # have side effects
                                meth = meth.fget
                            else:
                                try:
                                    meth = meth.__func__
                                except AttributeError:
                                    meth = meth.__get__(type_or_obj, type_)
                    except (AttributeError, TypeError):
                        continue
                    if meth.func_code is f.f_code:
                        break  # found
                else:
                    # Not found. Move onto the next class in MRO.
                    continue
                break  # found
            else:
                raise RuntimeError('super() called outside a method')

        # Dispatch to builtin super().
        if type_or_obj is not _SENTINEL:
            return _builtin_super(type_, type_or_obj)
        return _builtin_super(type_)


# --- exceptions


if PY3:
    FileNotFoundError = FileNotFoundError  # NOQA
    PermissionError = PermissionError  # NOQA
    ProcessLookupError = ProcessLookupError  # NOQA
    InterruptedError = InterruptedError  # NOQA
    ChildProcessError = ChildProcessError  # NOQA
    FileExistsError = FileExistsError  # NOQA
else:
    # https://github.com/PythonCharmers/python-future/blob/exceptions/
    #     src/future/types/exceptions/pep3151.py
    import platform

    def _instance_checking_exception(base_exception=Exception):
        def wrapped(instance_checker):
            class TemporaryClass(base_exception):

                def __init__(self, *args, **kwargs):
                    if len(args) == 1 and isinstance(args[0], TemporaryClass):
                        unwrap_me = args[0]
                        for attr in dir(unwrap_me):
                            if not attr.startswith('__'):
                                setattr(self, attr, getattr(unwrap_me, attr))
                    else:
                        super(TemporaryClass, self).__init__(*args, **kwargs)

                class __metaclass__(type):
                    def __instancecheck__(cls, inst):
                        return instance_checker(inst)

                    def __subclasscheck__(cls, classinfo):
                        value = sys.exc_info()[1]
                        return isinstance(value, cls)

            TemporaryClass.__name__ = instance_checker.__name__
            TemporaryClass.__doc__ = instance_checker.__doc__
            return TemporaryClass

        return wrapped

    @_instance_checking_exception(EnvironmentError)
    def FileNotFoundError(inst):
        return getattr(inst, 'errno', _SENTINEL) == errno.ENOENT

    @_instance_checking_exception(EnvironmentError)
    def ProcessLookupError(inst):
        return getattr(inst, 'errno', _SENTINEL) == errno.ESRCH

    @_instance_checking_exception(EnvironmentError)
    def PermissionError(inst):
        return getattr(inst, 'errno', _SENTINEL) in (
            errno.EACCES, errno.EPERM)

    @_instance_checking_exception(EnvironmentError)
    def InterruptedError(inst):
        return getattr(inst, 'errno', _SENTINEL) == errno.EINTR

    @_instance_checking_exception(EnvironmentError)
    def ChildProcessError(inst):
        return getattr(inst, 'errno', _SENTINEL) == errno.ECHILD

    @_instance_checking_exception(EnvironmentError)
    def FileExistsError(inst):
        return getattr(inst, 'errno', _SENTINEL) == errno.EEXIST

    if platform.python_implementation() != "CPython":
        try:
            raise OSError(errno.EEXIST, "perm")
        except FileExistsError:
            pass
        except OSError:
            raise RuntimeError(
                "broken or incompatible Python implementation, see: "
                "https://github.com/giampaolo/psutil/issues/1659")


# --- stdlib additions


# py 3.2 functools.lru_cache
# Taken from: http://code.activestate.com/recipes/578078
# Credit: Raymond Hettinger
try:
    from functools import lru_cache
except ImportError:
    try:
        from threading import RLock
    except ImportError:
        from dummy_threading import RLock

    _CacheInfo = collections.namedtuple(
        "CacheInfo", ["hits", "misses", "maxsize", "currsize"])

    class _HashedSeq(list):
        __slots__ = 'hashvalue'

        def __init__(self, tup, hash=hash):
            self[:] = tup
            self.hashvalue = hash(tup)

        def __hash__(self):
            return self.hashvalue

    def _make_key(args, kwds, typed,
                  kwd_mark=(_SENTINEL, ),
                  fasttypes=set((int, str, frozenset, type(None))),  # noqa
                  sorted=sorted, tuple=tuple, type=type, len=len):
        key = args
        if kwds:
            sorted_items = sorted(kwds.items())
            key += kwd_mark
            for item in sorted_items:
                key += item
        if typed:
            key += tuple(type(v) for v in args)
            if kwds:
                key += tuple(type(v) for k, v in sorted_items)
        elif len(key) == 1 and type(key[0]) in fasttypes:
            return key[0]
        return _HashedSeq(key)

    def lru_cache(maxsize=100, typed=False):
        """Least-recently-used cache decorator, see:
        http://docs.python.org/3/library/functools.html#functools.lru_cache
        """
        def decorating_function(user_function):
            cache = {}
            stats = [0, 0]
            HITS, MISSES = 0, 1
            make_key = _make_key
            cache_get = cache.get
            _len = len
            lock = RLock()
            root = []
            root[:] = [root, root, None, None]
            nonlocal_root = [root]
            PREV, NEXT, KEY, RESULT = 0, 1, 2, 3
            if maxsize == 0:
                def wrapper(*args, **kwds):
                    result = user_function(*args, **kwds)
                    stats[MISSES] += 1
                    return result
            elif maxsize is None:
                def wrapper(*args, **kwds):
                    key = make_key(args, kwds, typed)
                    result = cache_get(key, root)
                    if result is not root:
                        stats[HITS] += 1
                        return result
                    result = user_function(*args, **kwds)
                    cache[key] = result
                    stats[MISSES] += 1
                    return result
            else:
                def wrapper(*args, **kwds):
                    if kwds or typed:
                        key = make_key(args, kwds, typed)
                    else:
                        key = args
                    lock.acquire()
                    try:
                        link = cache_get(key)
                        if link is not None:
                            root, = nonlocal_root
                            link_prev, link_next, key, result = link
                            link_prev[NEXT] = link_next
                            link_next[PREV] = link_prev
                            last = root[PREV]
                            last[NEXT] = root[PREV] = link
                            link[PREV] = last
                            link[NEXT] = root
                            stats[HITS] += 1
                            return result
                    finally:
                        lock.release()
                    result = user_function(*args, **kwds)
                    lock.acquire()
                    try:
                        root, = nonlocal_root
                        if key in cache:
                            pass
                        elif _len(cache) >= maxsize:
                            oldroot = root
                            oldroot[KEY] = key
                            oldroot[RESULT] = result
                            root = nonlocal_root[0] = oldroot[NEXT]
                            oldkey = root[KEY]
                            root[KEY] = root[RESULT] = None
                            del cache[oldkey]
                            cache[key] = oldroot
                        else:
                            last = root[PREV]
                            link = [last, root, key, result]
                            last[NEXT] = root[PREV] = cache[key] = link
                        stats[MISSES] += 1
                    finally:
                        lock.release()
                    return result

            def cache_info():
                """Report cache statistics"""
                lock.acquire()
                try:
                    return _CacheInfo(stats[HITS], stats[MISSES], maxsize,
                                      len(cache))
                finally:
                    lock.release()

            def cache_clear():
                """Clear the cache and cache statistics"""
                lock.acquire()
                try:
                    cache.clear()
                    root = nonlocal_root[0]
                    root[:] = [root, root, None, None]
                    stats[:] = [0, 0]
                finally:
                    lock.release()

            wrapper.__wrapped__ = user_function
            wrapper.cache_info = cache_info
            wrapper.cache_clear = cache_clear
            return functools.update_wrapper(wrapper, user_function)

        return decorating_function


# python 3.3
try:
    from shutil import which
except ImportError:
    def which(cmd, mode=os.F_OK | os.X_OK, path=None):
        """Given a command, mode, and a PATH string, return the path which
        conforms to the given mode on the PATH, or None if there is no such
        file.

        `mode` defaults to os.F_OK | os.X_OK. `path` defaults to the result
        of os.environ.get("PATH"), or can be overridden with a custom search
        path.
        """
        def _access_check(fn, mode):
            return (os.path.exists(fn) and os.access(fn, mode) and
                    not os.path.isdir(fn))

        if os.path.dirname(cmd):
            if _access_check(cmd, mode):
                return cmd
            return None

        if path is None:
            path = os.environ.get("PATH", os.defpath)
        if not path:
            return None
        path = path.split(os.pathsep)

        if sys.platform == "win32":
            if os.curdir not in path:
                path.insert(0, os.curdir)

            pathext = os.environ.get("PATHEXT", "").split(os.pathsep)
            if any(cmd.lower().endswith(ext.lower()) for ext in pathext):
                files = [cmd]
            else:
                files = [cmd + ext for ext in pathext]
        else:
            files = [cmd]

        seen = set()
        for dir in path:
            normdir = os.path.normcase(dir)
            if normdir not in seen:
                seen.add(normdir)
                for thefile in files:
                    name = os.path.join(dir, thefile)
                    if _access_check(name, mode):
                        return name
        return None


# python 3.3
try:
    from shutil import get_terminal_size
except ImportError:
    def get_terminal_size(fallback=(80, 24)):
        try:
            import fcntl
            import struct
            import termios
        except ImportError:
            return fallback
        else:
            try:
                # This should work on Linux.
                res = struct.unpack(
                    'hh', fcntl.ioctl(1, termios.TIOCGWINSZ, '1234'))
                return (res[1], res[0])
            except Exception:
                return fallback


# python 3.3
try:
    from subprocess import TimeoutExpired as SubprocessTimeoutExpired
except ImportError:
    class SubprocessTimeoutExpired(Exception):
        pass


# python 3.5
try:
    from contextlib import redirect_stderr
except ImportError:
    @contextlib.contextmanager
    def redirect_stderr(new_target):
        original = sys.stderr
        try:
            sys.stderr = new_target
            yield new_target
        finally:
            sys.stderr = original