diff -r 7757e98a9f3b Lib/gzip.py
--- a/Lib/gzip.py	Tue Mar 17 06:56:11 2015 +0200
+++ b/Lib/gzip.py	Sun Mar 22 23:14:01 2015 +0100
@@ -334,17 +334,20 @@
         if self.fileobj is None:
             raise ValueError("write() on closed GzipFile object")
 
-        # Convert data type if called by io.BufferedWriter.
-        if isinstance(data, memoryview):
-            data = data.tobytes()
+        if isinstance(data, bytes):
+            length = len(data)
+        else:
+            # accept any data that supports the buffer protocol
+            data = memoryview(data)
+            length = data.nbytes
 
-        if len(data) > 0:
-            self.size = self.size + len(data)
+        if length > 0:
+            self.fileobj.write(self.compress.compress(data))
+            self.size += length
             self.crc = zlib.crc32(data, self.crc) & 0xffffffff
-            self.fileobj.write( self.compress.compress(data) )
-            self.offset += len(data)
+            self.offset += length
 
-        return len(data)
+        return length
 
     def read(self, size=-1):
         self._check_closed()
diff -r 7757e98a9f3b Lib/test/test_gzip.py
--- a/Lib/test/test_gzip.py	Tue Mar 17 06:56:11 2015 +0200
+++ b/Lib/test/test_gzip.py	Sun Mar 22 23:14:01 2015 +0100
@@ -6,6 +6,7 @@
 import os
 import io
 import struct
+import array
 gzip = support.import_module('gzip')
 
 data1 = b"""  int length=DEFAULTALLOC, err = Z_OK;
@@ -43,6 +44,14 @@
 
 
 class TestGzip(BaseTest):
+    def write_and_read_back(self, data, mode='b'):
+        b_data = bytes(data)
+        with gzip.GzipFile(self.filename, 'w'+mode) as f:
+            l = f.write(data)
+        self.assertEqual(l, len(b_data))
+        with gzip.GzipFile(self.filename, 'r'+mode) as f:
+            self.assertEqual(f.read(), b_data)
+            
     def test_write(self):
         with gzip.GzipFile(self.filename, 'wb') as f:
             f.write(data1 * 50)
@@ -57,13 +66,6 @@
         # Test multiple close() calls.
         f.close()
 
-    def test_read(self):
-        self.test_write()
-        # Try reading.
-        with gzip.GzipFile(self.filename, 'r') as f:
-            d = f.read()
-        self.assertEqual(d, data1*50)
-
     def test_read1(self):
         self.test_write()
         blocks = []
@@ -130,6 +132,39 @@
                 if not ztxt: break
         self.assertEqual(contents, b'a'*201)
 
+    # The following test_write_xy methods test that write accepts
+    # the corresponding bytes-like object type as input
+    # and that the data written equals bytes(xy) in all cases.
+    def test_write_memoryview(self):
+        data = memoryview(data1 * 50)
+        self.write_and_read_back(data)
+        m = memoryview(bytes(range(256)))
+        data = m.cast('B', shape=[8,8,4])
+        self.write_and_read_back(data)
+
+    def test_write_bytearray(self):
+        data = bytearray(data1 * 50)
+        self.write_and_read_back(data)
+
+    def test_write_array(self):
+        for typecode in array.typecodes:
+            data = array.array(typecode, data1 * 80)
+            self.write_and_read_back(data)
+        
+    def test_write_incompatible_type(self):
+        # Test that non-bytes-like types raise TypeError.
+        for data in (data1.decode('utf-8'), list(data1)):
+            self.assertRaises(TypeError, self.write_and_read_back, data)
+
+    def test_write_retry(self):
+        # Issue #21560: attempts to write incompatible types
+        # should not affect the state of the fileobject
+        data = data1.decode('utf-8')
+        try:
+            self.write_and_read_back(data * 50)
+        except TypeError:
+            self.write_and_read_back(data1 * 50)
+                      
     def test_exclusive_write(self):
         with gzip.GzipFile(self.filename, 'xb') as f:
             f.write(data1 * 50)