bpo-32166: Drop Python 3.4 code from asyncio (#4612)

* Drop Python 3.4 code from asyncio

* Fix notes

* Add missing imports

* Restore comment

* Resort imports

* Drop Python 3.4-3.5 specific code

* Drop redunant check

* Fix tests

* Restore _COROUTINE_TYPES order

* Remove useless code

Lib/asyncio/unix_events.py

@@ -38,13 +38,6 @@ def _sighandler_noop(signum, frame):
     pass
 
 
-try:
-    _fspath = os.fspath
-except AttributeError:
-    # Python 3.5 or earlier
-    _fspath = lambda path: path
-
-
 class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
     """Unix event loop.
 
@@ -74,7 +67,7 @@ class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
         Raise RuntimeError if there is a problem setting up the handler.
         """
         if (coroutines.iscoroutine(callback)
-        or coroutines.iscoroutinefunction(callback)):
+                or coroutines.iscoroutinefunction(callback)):
             raise TypeError("coroutines cannot be used "
                             "with add_signal_handler()")
         self._check_signal(sig)
@@ -226,7 +219,7 @@ class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
                 raise ValueError(
                     'path and sock can not be specified at the same time')
 
-            path = _fspath(path)
+            path = os.fspath(path)
             sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM, 0)
             try:
                 sock.setblocking(False)
@@ -260,7 +253,7 @@ class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
                 raise ValueError(
                     'path and sock can not be specified at the same time')
 
-            path = _fspath(path)
+            path = os.fspath(path)
             sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
 
             # Check for abstract socket. `str` and `bytes` paths are supported.
@@ -272,7 +265,8 @@ class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
                     pass
                 except OSError as err:
                     # Directory may have permissions only to create socket.
-                    logger.error('Unable to check or remove stale UNIX socket %r: %r', path, err)
+                    logger.error('Unable to check or remove stale UNIX socket '
+                                 '%r: %r', path, err)
 
             try:
                 sock.bind(path)
@@ -306,18 +300,6 @@ class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
         return server
 
 
-if hasattr(os, 'set_blocking'):
-    def _set_nonblocking(fd):
-        os.set_blocking(fd, False)
-else:
-    import fcntl
-
-    def _set_nonblocking(fd):
-        flags = fcntl.fcntl(fd, fcntl.F_GETFL)
-        flags = flags | os.O_NONBLOCK
-        fcntl.fcntl(fd, fcntl.F_SETFL, flags)
-
-
 class _UnixReadPipeTransport(transports.ReadTransport):
 
     max_size = 256 * 1024  # max bytes we read in one event loop iteration
@@ -340,7 +322,7 @@ class _UnixReadPipeTransport(transports.ReadTransport):
             self._protocol = None
             raise ValueError("Pipe transport is for pipes/sockets only.")
 
-        _set_nonblocking(self._fileno)
+        os.set_blocking(self._fileno, False)
 
         self._loop.call_soon(self._protocol.connection_made, self)
         # only start reading when connection_made() has been called
@@ -469,7 +451,7 @@ class _UnixWritePipeTransport(transports._FlowControlMixin,
             raise ValueError("Pipe transport is only for "
                              "pipes, sockets and character devices")
 
-        _set_nonblocking(self._fileno)
+        os.set_blocking(self._fileno, False)
         self._loop.call_soon(self._protocol.connection_made, self)
 
         # On AIX, the reader trick (to be notified when the read end of the
@@ -648,22 +630,6 @@ class _UnixWritePipeTransport(transports._FlowControlMixin,
             self._loop = None
 
 
-if hasattr(os, 'set_inheritable'):
-    # Python 3.4 and newer
-    _set_inheritable = os.set_inheritable
-else:
-    import fcntl
-
-    def _set_inheritable(fd, inheritable):
-        cloexec_flag = getattr(fcntl, 'FD_CLOEXEC', 1)
-
-        old = fcntl.fcntl(fd, fcntl.F_GETFD)
-        if not inheritable:
-            fcntl.fcntl(fd, fcntl.F_SETFD, old | cloexec_flag)
-        else:
-            fcntl.fcntl(fd, fcntl.F_SETFD, old & ~cloexec_flag)
-
-
 class _UnixSubprocessTransport(base_subprocess.BaseSubprocessTransport):
 
     def _start(self, args, shell, stdin, stdout, stderr, bufsize, **kwargs):
@@ -675,12 +641,6 @@ class _UnixSubprocessTransport(base_subprocess.BaseSubprocessTransport):
             # other end).  Notably this is needed on AIX, and works
             # just fine on other platforms.
             stdin, stdin_w = socket.socketpair()
-
-            # Mark the write end of the stdin pipe as non-inheritable,
-            # needed by close_fds=False on Python 3.3 and older
-            # (Python 3.4 implements the PEP 446, socketpair returns
-            # non-inheritable sockets)
-            _set_inheritable(stdin_w.fileno(), False)
         self._proc = subprocess.Popen(
             args, shell=shell, stdin=stdin, stdout=stdout, stderr=stderr,
             universal_newlines=False, bufsize=bufsize, **kwargs)
@@ -1035,8 +995,8 @@ class _UnixDefaultEventLoopPolicy(events.BaseDefaultEventLoopPolicy):
 
         super().set_event_loop(loop)
 
-        if self._watcher is not None and \
-            isinstance(threading.current_thread(), threading._MainThread):
+        if (self._watcher is not None and
+                isinstance(threading.current_thread(), threading._MainThread)):
             self._watcher.attach_loop(loop)
 
     def get_child_watcher(self):