Let PipedCompressionWriter/-Reader derive from IOBase

This is the proper thing to do and also gives us a couple of methods for
free, in particular readlines().

This also allows us to get rid of the Closing mixin.

Closes #129

src/xopen/__init__.py

@@ -33,7 +33,6 @@
 import subprocess
 import tempfile
 import time
-from abc import ABC, abstractmethod
 from subprocess import Popen, PIPE, DEVNULL
 from typing import (
     Optional,
@@ -157,30 +156,7 @@ def _can_read_concatenated_gz(program: str) -> bool:
         os.remove(temp_path)
 
 
-class Closing(ABC):
-    """
-    Inherit from this class and implement a close() method to offer context
-    manager functionality.
-    """
-
-    def __enter__(self):
-        return self
-
-    def __exit__(self, *exc_info):
-        self.close()
-
-    def __del__(self):
-        try:
-            self.close()
-        except Exception:
-            pass
-
-    @abstractmethod
-    def close(self):
-        """Called when exiting the context manager"""
-
-
-class PipedCompressionWriter(Closing):
+class PipedCompressionWriter(io.IOBase):
     """
     Write Compressed files by running an external process and piping into it.
     """
@@ -216,7 +192,6 @@ def __init__(
 
         # TODO use a context manager
         self.outfile = open(path, mode[0] + "b")
-        self.closed: bool = False
         self.name: str = str(os.fspath(path))
         self._mode: str = mode
         self._program_args: List[str] = program_args
@@ -283,7 +258,7 @@ def write(self, arg: AnyStr) -> int:
     def close(self) -> None:
         if self.closed:
             return
-        self.closed = True
+        super().close()
         self._file.close()
         retcode = self.process.wait()
         self.outfile.close()
@@ -311,7 +286,7 @@ def __next__(self):
         raise io.UnsupportedOperation("not readable")
 
 
-class PipedCompressionReader(Closing):
+class PipedCompressionReader(io.IOBase):
     """
     Open a pipe to a process for reading a compressed file.
     """
@@ -371,7 +346,6 @@ def __init__(
             )
         else:
             self._file = self.process.stdout
-        self.closed = False
         self._wait_for_output_or_process_exit()
         self._raise_if_error()
 
@@ -387,7 +361,7 @@ def __repr__(self):
     def close(self) -> None:
         if self.closed:
             return
-        self.closed = True
+        super().close()
         retcode = self.process.poll()
         check_allowed_code_and_message = False
         if retcode is None:

tests/test_piped.py

@@ -175,6 +175,12 @@ def test_reader_readline_text(reader):
         assert f.readline() == CONTENT_LINES[0]
 
 
+def test_reader_readlines(reader):
+    opener, extension = reader
+    with opener(TEST_DIR / f"file.txt{extension}", "r") as f:
+        assert f.readlines() == CONTENT_LINES
+
+
 @pytest.mark.parametrize("threads", [None, 1, 2])
 def test_piped_reader_iter(threads, threaded_reader):
     opener, extension = threaded_reader