bpo-26253: don't add compresslevel as an attribute

In tarfile, compresslevel will be simply passed around.

Also added 'versionadded' to stream compression level setting

Author: jarondl

Doc/library/tarfile.rst

@@ -149,6 +149,9 @@ Some facts and figures:
    .. versionchanged:: 3.6
       The *name* parameter accepts a :term:`path-like object`.
 
+   .. versionchanged:: 3.7
+      The *compresslevel* keyword argument also works for streams.
+
 
 .. class:: TarFile
 

Lib/tarfile.py

@@ -344,7 +344,7 @@ class _Stream:
     """
 
     def __init__(self, name, mode, comptype, fileobj, bufsize,
-                 compresslevel=9):
+                 compresslevel):
         """Construct a _Stream object.
         """
         self._extfileobj = True
@@ -358,15 +358,14 @@ def __init__(self, name, mode, comptype, fileobj, bufsize,
             fileobj = _StreamProxy(fileobj)
             comptype = fileobj.getcomptype()
 
-        self.name = name or ""
-        self.mode = mode
+        self.name     = name or ""
+        self.mode     = mode
         self.comptype = comptype
-        self.fileobj = fileobj
-        self.bufsize = bufsize
-        self.compresslevel = compresslevel
-        self.buf = b""
-        self.pos = 0
-        self.closed = False
+        self.fileobj  = fileobj
+        self.bufsize  = bufsize
+        self.buf      = b""
+        self.pos      = 0
+        self.closed   = False
 
         try:
             if comptype == "gz":
@@ -380,7 +379,7 @@ def __init__(self, name, mode, comptype, fileobj, bufsize,
                     self._init_read_gz()
                     self.exception = zlib.error
                 else:
-                    self._init_write_gz()
+                    self._init_write_gz(compresslevel)
 
             elif comptype == "bz2":
                 try:
@@ -392,7 +391,7 @@ def __init__(self, name, mode, comptype, fileobj, bufsize,
                     self.cmp = bz2.BZ2Decompressor()
                     self.exception = OSError
                 else:
-                    self.cmp = bz2.BZ2Compressor(self.compresslevel)
+                    self.cmp = bz2.BZ2Compressor(compresslevel)
 
             elif comptype == "xz":
                 try:
@@ -419,10 +418,10 @@ def __del__(self):
         if hasattr(self, "closed") and not self.closed:
             self.close()
 
-    def _init_write_gz(self):
+    def _init_write_gz(self, compresslevel):
         """Initialize for writing with gzip compression.
         """
-        self.cmp = self.zlib.compressobj(self.compresslevel,
+        self.cmp = self.zlib.compressobj(compresslevel,
                                          self.zlib.DEFLATED,
                                          -self.zlib.MAX_WBITS,
                                          self.zlib.DEF_MEM_LEVEL,