Simplify usage of LZMAFile's fileobj support, like with BZ2File.

Doc/library/lzma.rst

@@ -29,18 +29,20 @@ from multiple threads, it is necessary to protect it with a lock.
 Reading and writing compressed files
 ------------------------------------
 
-.. class:: LZMAFile(filename=None, mode="r", \*, fileobj=None, format=None, check=-1, preset=None, filters=None)
+.. class:: LZMAFile(filename=None, mode="r", \*, format=None, check=-1, preset=None, filters=None)
 
-   Open an LZMA-compressed file.
+   Open an LZMA-compressed file in binary mode.
 
-   An :class:`LZMAFile` can wrap an existing :term:`file object` (given by
-   *fileobj*), or operate directly on a named file (named by *filename*).
-   Exactly one of these two parameters should be provided. If *fileobj* is
-   provided, it is not closed when the :class:`LZMAFile` is closed.
+   An :class:`LZMAFile` can wrap an already-open :term:`file object`, or operate
+   directly on a named file. The *filename* argument specifies either the file
+   object to wrap, or the name of the file to open (as a :class:`str` or
+   :class:`bytes` object). When wrapping an existing file object, the wrapped
+   file will not be closed when the :class:`LZMAFile` is closed.
 
    The *mode* argument can be either ``"r"`` for reading (default), ``"w"`` for
-   overwriting, or ``"a"`` for appending. If *fileobj* is provided, a mode of
-   ``"w"`` does not truncate the file, and is instead equivalent to ``"a"``.
+   overwriting, or ``"a"`` for appending. If *filename* is an existing file
+   object, a mode of ``"w"`` does not truncate the file, and is instead
+   equivalent to ``"a"``.
 
    When opening a file for reading, the input file may be the concatenation of
    multiple separate compressed streams. These are transparently decoded as a
@@ -360,7 +362,7 @@ Writing compressed data to an already-open file::
    import lzma
    with open("file.xz", "wb") as f:
        f.write(b"This data will not be compressed\n")
-       with lzma.LZMAFile(fileobj=f, mode="w") as lzf:
+       with lzma.LZMAFile(f, "w") as lzf:
            lzf.write(b"This *will* be compressed\n")
        f.write(b"Not compressed\n")
 

Lib/lzma.py

@@ -46,13 +46,12 @@ class LZMAFile(io.BufferedIOBase):
     """
 
     def __init__(self, filename=None, mode="r", *,
-                 fileobj=None, format=None, check=-1,
-                 preset=None, filters=None):
-        """Open an LZMA-compressed file.
+                 format=None, check=-1, preset=None, filters=None):
+        """Open an LZMA-compressed file in binary mode.
 
-        If filename is given, open the named file. Otherwise, operate on
-        the file object given by fileobj. Exactly one of these two
-        parameters should be provided.
+        filename can be either an actual file name (given as a str or
+        bytes object), in which case the named file is opened, or it can
+        be an existing file object to read from or write to.
 
         mode can be "r" for reading (default), "w" for (over)writing, or
         "a" for appending.
@@ -119,16 +118,16 @@ class LZMAFile(io.BufferedIOBase):
         else:
             raise ValueError("Invalid mode: {!r}".format(mode))
 
-        if filename is not None and fileobj is None:
+        if isinstance(filename, (str, bytes)):
             mode += "b"
             self._fp = open(filename, mode)
             self._closefp = True
             self._mode = mode_code
-        elif fileobj is not None and filename is None:
-            self._fp = fileobj
+        elif hasattr(filename, "read") or hasattr(filename, "write"):
+            self._fp = filename
             self._mode = mode_code
         else:
-            raise ValueError("Must give exactly one of filename and fileobj")
+            raise TypeError("filename must be a str or bytes object, or a file")
 
     def close(self):
         """Flush and close the file.

Lib/tarfile.py

@@ -1681,8 +1681,7 @@ class TarFile(object):
         except ImportError:
             raise CompressionError("lzma module is not available")
 
-        fileobj = lzma.LZMAFile(filename=name if fileobj is None else None,
-                mode=mode, fileobj=fileobj, preset=preset)
+        fileobj = lzma.LZMAFile(fileobj or name, mode, preset=preset)
 
         try:
             t = cls.taropen(name, mode, fileobj, **kwargs)

Misc/NEWS

@@ -18,8 +18,8 @@ Library
 - The bz2 module now contains an open() function, allowing compressed files to
   conveniently be opened in text mode as well as binary mode.
 
-- BZ2File.__init__() now accepts a file object as its first argument, rather
-  than requiring a separate "fileobj" argument.
+- BZ2File.__init__() and LZMAFile.__init__() now accept a file object as their
+  first argument, rather than requiring a separate "fileobj" argument.
 
 - gzip.open() now accepts file objects as well as filenames.