diff --git a/tests/qemu-iotests/qcow2.py b/tests/qemu-iotests/qcow2.py
index 94a07b2f6f..539f5a186b 100755
--- a/tests/qemu-iotests/qcow2.py
+++ b/tests/qemu-iotests/qcow2.py
@@ -4,6 +4,7 @@ import sys
 import struct
 import string
 
+
 class QcowHeaderExtension:
 
     def __init__(self, magic, length, data):
@@ -11,14 +12,15 @@ class QcowHeaderExtension:
             padding = 8 - (length % 8)
             data += b"\0" * padding
 
-        self.magic  = magic
+        self.magic = magic
         self.length = length
-        self.data   = data
+        self.data = data
 
     @classmethod
     def create(cls, magic, data):
         return QcowHeaderExtension(magic, len(data), data)
 
+
 class QcowHeader:
 
     uint32_t = 'I'
@@ -26,27 +28,27 @@ class QcowHeader:
 
     fields = [
         # Version 2 header fields
-        [ uint32_t, '%#x',  'magic' ],
-        [ uint32_t, '%d',   'version' ],
-        [ uint64_t, '%#x',  'backing_file_offset' ],
-        [ uint32_t, '%#x',  'backing_file_size' ],
-        [ uint32_t, '%d',   'cluster_bits' ],
-        [ uint64_t, '%d',   'size' ],
-        [ uint32_t, '%d',   'crypt_method' ],
-        [ uint32_t, '%d',   'l1_size' ],
-        [ uint64_t, '%#x',  'l1_table_offset' ],
-        [ uint64_t, '%#x',  'refcount_table_offset' ],
-        [ uint32_t, '%d',   'refcount_table_clusters' ],
-        [ uint32_t, '%d',   'nb_snapshots' ],
-        [ uint64_t, '%#x',  'snapshot_offset' ],
+        [uint32_t, '%#x',  'magic'],
+        [uint32_t, '%d',   'version'],
+        [uint64_t, '%#x',  'backing_file_offset'],
+        [uint32_t, '%#x',  'backing_file_size'],
+        [uint32_t, '%d',   'cluster_bits'],
+        [uint64_t, '%d',   'size'],
+        [uint32_t, '%d',   'crypt_method'],
+        [uint32_t, '%d',   'l1_size'],
+        [uint64_t, '%#x',  'l1_table_offset'],
+        [uint64_t, '%#x',  'refcount_table_offset'],
+        [uint32_t, '%d',   'refcount_table_clusters'],
+        [uint32_t, '%d',   'nb_snapshots'],
+        [uint64_t, '%#x',  'snapshot_offset'],
 
         # Version 3 header fields
-        [ uint64_t, 'mask', 'incompatible_features' ],
-        [ uint64_t, 'mask', 'compatible_features' ],
-        [ uint64_t, 'mask', 'autoclear_features' ],
-        [ uint32_t, '%d',   'refcount_order' ],
-        [ uint32_t, '%d',   'header_length' ],
-    ];
+        [uint64_t, 'mask', 'incompatible_features'],
+        [uint64_t, 'mask', 'compatible_features'],
+        [uint64_t, 'mask', 'autoclear_features'],
+        [uint32_t, '%d',   'refcount_order'],
+        [uint32_t, '%d',   'header_length'],
+    ]
 
     fmt = '>' + ''.join(field[0] for field in fields)
 
@@ -59,7 +61,7 @@ class QcowHeader:
 
         header = struct.unpack(QcowHeader.fmt, buf)
         self.__dict__ = dict((field[2], header[i])
-            for i, field in enumerate(QcowHeader.fields))
+                             for i, field in enumerate(QcowHeader.fields))
 
         self.set_defaults()
         self.cluster_size = 1 << self.cluster_bits
@@ -96,7 +98,8 @@ class QcowHeader:
             else:
                 padded = (length + 7) & ~7
                 data = fd.read(padded)
-                self.extensions.append(QcowHeaderExtension(magic, length, data))
+                self.extensions.append(QcowHeaderExtension(magic, length,
+                                                           data))
 
     def update_extensions(self, fd):
 
@@ -108,14 +111,13 @@ class QcowHeader:
             fd.write(buf)
             fd.write(ex.data)
 
-        if self.backing_file != None:
+        if self.backing_file is not None:
             self.backing_file_offset = fd.tell()
             fd.write(self.backing_file)
 
         if fd.tell() > self.cluster_size:
             raise Exception("I think I just broke the image...")
 
-
     def update(self, fd):
         header_bytes = self.header_length
 
@@ -163,19 +165,21 @@ def cmd_dump_header(fd):
     h.dump()
     h.dump_extensions()
 
+
 def cmd_dump_header_exts(fd):
     h = QcowHeader(fd)
     h.dump_extensions()
 
+
 def cmd_set_header(fd, name, value):
     try:
         value = int(value, 0)
-    except:
+    except ValueError:
         print("'%s' is not a valid number" % value)
         sys.exit(1)
 
     fields = (field[2] for field in QcowHeader.fields)
-    if not name in fields:
+    if name not in fields:
         print("'%s' is not a known header field" % name)
         sys.exit(1)
 
@@ -183,25 +187,29 @@ def cmd_set_header(fd, name, value):
     h.__dict__[name] = value
     h.update(fd)
 
+
 def cmd_add_header_ext(fd, magic, data):
     try:
         magic = int(magic, 0)
-    except:
+    except ValueError:
         print("'%s' is not a valid magic number" % magic)
         sys.exit(1)
 
     h = QcowHeader(fd)
-    h.extensions.append(QcowHeaderExtension.create(magic, data.encode('ascii')))
+    h.extensions.append(QcowHeaderExtension.create(magic,
+                                                   data.encode('ascii')))
     h.update(fd)
 
+
 def cmd_add_header_ext_stdio(fd, magic):
     data = sys.stdin.read()
     cmd_add_header_ext(fd, magic, data)
 
+
 def cmd_del_header_ext(fd, magic):
     try:
         magic = int(magic, 0)
-    except:
+    except ValueError:
         print("'%s' is not a valid magic number" % magic)
         sys.exit(1)
 
@@ -219,12 +227,13 @@ def cmd_del_header_ext(fd, magic):
 
     h.update(fd)
 
+
 def cmd_set_feature_bit(fd, group, bit):
     try:
         bit = int(bit, 0)
         if bit < 0 or bit >= 64:
             raise ValueError
-    except:
+    except ValueError:
         print("'%s' is not a valid bit number in range [0, 64)" % bit)
         sys.exit(1)
 
@@ -236,21 +245,24 @@ def cmd_set_feature_bit(fd, group, bit):
     elif group == 'autoclear':
         h.autoclear_features |= 1 << bit
     else:
-        print("'%s' is not a valid group, try 'incompatible', 'compatible', or 'autoclear'" % group)
+        print("'%s' is not a valid group, try "
+              "'incompatible', 'compatible', or 'autoclear'" % group)
         sys.exit(1)
 
     h.update(fd)
 
+
 cmds = [
-    [ 'dump-header',          cmd_dump_header,          0, 'Dump image header and header extensions' ],
-    [ 'dump-header-exts',     cmd_dump_header_exts,     0, 'Dump image header extensions' ],
-    [ 'set-header',           cmd_set_header,           2, 'Set a field in the header'],
-    [ 'add-header-ext',       cmd_add_header_ext,       2, 'Add a header extension' ],
-    [ 'add-header-ext-stdio', cmd_add_header_ext_stdio, 1, 'Add a header extension, data from stdin' ],
-    [ 'del-header-ext',       cmd_del_header_ext,       1, 'Delete a header extension' ],
-    [ 'set-feature-bit',      cmd_set_feature_bit,      2, 'Set a feature bit'],
+    ['dump-header',          cmd_dump_header,          0, 'Dump image header and header extensions'],
+    ['dump-header-exts',     cmd_dump_header_exts,     0, 'Dump image header extensions'],
+    ['set-header',           cmd_set_header,           2, 'Set a field in the header'],
+    ['add-header-ext',       cmd_add_header_ext,       2, 'Add a header extension'],
+    ['add-header-ext-stdio', cmd_add_header_ext_stdio, 1, 'Add a header extension, data from stdin'],
+    ['del-header-ext',       cmd_del_header_ext,       1, 'Delete a header extension'],
+    ['set-feature-bit',      cmd_set_feature_bit,      2, 'Set a feature bit'],
 ]
 
+
 def main(filename, cmd, args):
     fd = open(filename, "r+b")
     try:
@@ -267,6 +279,7 @@ def main(filename, cmd, args):
     finally:
         fd.close()
 
+
 def usage():
     print("Usage: %s <file> <cmd> [<arg>, ...]" % sys.argv[0])
     print("")
@@ -274,6 +287,7 @@ def usage():
     for name, handler, num_args, desc in cmds:
         print("    %-20s - %s" % (name, desc))
 
+
 if __name__ == '__main__':
     if len(sys.argv) < 3:
         usage()
