@@ -336,7 +336,8 @@ class _Stream:
       _Stream is intended to be used only internally.
    """

-    def __init__(self, name, mode, comptype, fileobj, bufsize):
        """Construct a _Stream object.
        """
        self._extfileobj = True
@@ -371,7 +372,7 @@ def __init__(self, name, mode, comptype, fileobj, bufsize):
                    self._init_read_gz()
                    self.exception = zlib.error
                else:
-                    self._init_write_gz()

            elif comptype == "bz2":
                try:
@@ -383,7 +384,7 @@ def __init__(self, name, mode, comptype, fileobj, bufsize):
                    self.cmp = bz2.BZ2Decompressor()
                    self.exception = OSError
                else:
-                    self.cmp = bz2.BZ2Compressor()

            elif comptype == "xz":
                try:
@@ -410,13 +411,14 @@ def __del__(self):
        if hasattr(self, "closed") and not self.closed:
            self.close()

-    def _init_write_gz(self):
        """Initialize for writing with gzip compression.
        """
-        self.cmp = self.zlib.compressobj(9, self.zlib.DEFLATED,
-                                            -self.zlib.MAX_WBITS,
-                                            self.zlib.DEF_MEM_LEVEL,
-                                            0)
        timestamp = struct.pack("<L", int(time.time()))
        self.__write(b"\037\213\010\010" + timestamp + b"\002\377")
        if self.name.endswith(".gz"):
@@ -1649,7 +1651,9 @@ def not_compressed(comptype):
            if filemode not in ("r", "w"):
                raise ValueError("mode must be 'r' or 'w'")

-            stream = _Stream(name, filemode, comptype, fileobj, bufsize)
            try:
                t = cls(name, filemode, stream, **kwargs)
            except:

@@ -1532,6 +1532,74 @@ class Bz2StreamWriteTest(Bz2Test, StreamWriteTest):
class LzmaStreamWriteTest(LzmaTest, StreamWriteTest):
    decompressor = lzma.LZMADecompressor if lzma else None


class GNUWriteTest(unittest.TestCase):
    # This testcase checks for correct creation of GNU Longname

diff --git a/Misc/NEWS.d/next/Library/2017-07-31-13-35-28.bpo-26253.8v_sCs.rst b/Misc/NEWS.d/next/Library/2017-07-31-13-35-28.bpo-26253.8v_sCs.rst
@@ -0,0 +1,2 @@