diff -r 8270c5f59d26 Lib/test/test_zipfile.py
--- a/Lib/test/test_zipfile.py	Mon May 02 18:49:30 2011 +0200
+++ b/Lib/test/test_zipfile.py	Mon May 02 19:17:46 2011 +0200
@@ -359,6 +359,15 @@
             with open(TESTFN, "rb") as f:
                 self.assertEqual(zipfp.read(TESTFN), f.read())
 
+    def test_writefp_default_name(self):
+        """Check that calling ZipFile.write without arcname specified
+        produces the expected result."""
+        with zipfile.ZipFile(TESTFN2, "w") as zipfp:
+            fp = io.BytesIO("hello world".encode("ascii"))
+            zipfp.writefp("a.txt", fp)
+        with zipfile.ZipFile(TESTFN2, "r") as zipfp:
+          self.assertEqual(zipfp.read("a.txt"), b"hello world")
+
     @skipUnless(zlib, "requires zlib")
     def test_per_file_compression(self):
         """Check that files within a Zip archive can have different
diff -r 8270c5f59d26 Lib/zipfile.py
--- a/Lib/zipfile.py	Mon May 02 18:49:30 2011 +0200
+++ b/Lib/zipfile.py	Mon May 02 19:17:46 2011 +0200
@@ -1189,6 +1189,42 @@
         self.filelist.append(zinfo)
         self.NameToInfo[zinfo.filename] = zinfo
 
+    def writefp(self, zinfo_or_arcname, fp):
+        """Write a file into the archive.  The contents is in 'fp'
+        which is a file object.
+        'zinfo_or_arcname' is either a ZipInfo instance or the name of the
+        file in the archive.
+        Note: this always store file using ZIP_STORED compression method.
+        """
+        if not isinstance(zinfo_or_arcname, ZipInfo):
+            zinfo = ZipInfo(filename=zinfo_or_arcname,
+                            date_time=time.localtime(time.time())[:6])
+            zinfo.compress_type = self.compression
+            zinfo.external_attr = 0o600 << 16
+        else:
+            zinfo = zinfo_or_arcname
+        zinfo.header_offset = self.fp.tell()    # Start of header bytes
+        zinfo.flag_bits = 0x08
+        self._didModify = True
+        self.fp.write(zinfo.FileHeader())
+        CRC = 0
+        file_size = 0
+        while 1:
+            buf = fp.read(1024 * 8)
+            if not buf:
+                break
+            file_size = file_size + len(buf)
+            CRC = crc32(buf, CRC) & 0xffffffff
+            self.fp.write(buf)
+        fp.close()
+        zinfo.file_size = file_size
+        zinfo.compress_size = file_size
+        zinfo.CRC = CRC & 0xffffffff       # CRC-32 checksum
+        self.fp.write(struct.pack("<LLL", zinfo.CRC, zinfo.compress_size,
+                                  zinfo.file_size))
+        self.filelist.append(zinfo)
+        self.NameToInfo[zinfo.filename] = zinfo
+
     def __del__(self):
         """Call the "close()" method in case the user forgot."""
         self.close()