Issue #9962: GzipFile now has the peek() method.

Lib/test/test_gzip.py

@@ -286,6 +286,28 @@ class TestGzip(unittest.TestCase):
         with gzip.GzipFile(fileobj=buf, mode="rb") as f:
             self.assertEqual(f.read(), uncompressed)
 
+    def test_peek(self):
+        uncompressed = data1 * 200
+        with gzip.GzipFile(self.filename, "wb") as f:
+            f.write(uncompressed)
+
+        def sizes():
+            while True:
+                for n in range(5, 50, 10):
+                    yield n
+
+        with gzip.GzipFile(self.filename, "rb") as f:
+            f.max_read_chunk = 33
+            nread = 0
+            for n in sizes():
+                s = f.peek(n)
+                if s == b'':
+                    break
+                self.assertEqual(f.read(len(s)), s)
+                nread += len(s)
+            self.assertEqual(f.read(100), b'')
+            self.assertEqual(nread, len(uncompressed))
+
     # Testing compress/decompress shortcut functions
 
     def test_compress(self):