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Re: [PATCH v12 09/11] qcow2_format.py: collect fields to dump in JSON fo

From: Andrey Shinkevich
Subject: Re: [PATCH v12 09/11] qcow2_format.py: collect fields to dump in JSON format
Date: Thu, 6 Aug 2020 12:08:40 +0300
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.9.0

On 05.08.2020 19:58, Vladimir Sementsov-Ogievskiy wrote:
30.07.2020 17:15, Andrey Shinkevich wrote:
As __dict__ is being extended with class members we do not want to
print, add the to_dict() method to classes that returns a dictionary
with desired fields and their values. Extend it in subclass when
necessary to print the final dictionary in the JSON output which

Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
  tests/qemu-iotests/qcow2_format.py | 34 ++++++++++++++++++++++++++++++++++
  1 file changed, 34 insertions(+)

diff --git a/tests/qemu-iotests/qcow2_format.py b/tests/qemu-iotests/qcow2_format.py
index 2000de3..a4114cb 100644
--- a/tests/qemu-iotests/qcow2_format.py
+++ b/tests/qemu-iotests/qcow2_format.py
@@ -119,6 +119,9 @@ class Qcow2Struct(metaclass=Qcow2StructMeta):
                print('{:<25} {}'.format(f[2], value_str))
  +    def to_dict(self):
+        return dict((f[2], self.__dict__[f[2]]) for f in self.fields)
    class Qcow2BitmapExt(Qcow2Struct):
  @@ -151,6 +154,11 @@ class Qcow2BitmapExt(Qcow2Struct):
  +    def to_dict(self):
+        fields_dict = super().to_dict()
+        fields_dict['bitmap_directory'] = self.bitmap_directory
+        return fields_dict
    class Qcow2BitmapDirEntry(Qcow2Struct):
  @@ -189,6 +197,14 @@ class Qcow2BitmapDirEntry(Qcow2Struct):
          super(Qcow2BitmapDirEntry, self).dump()
  +    def to_dict(self):
+        fields_dict = super().to_dict()
+        fields_dict['bitmap_table'] = self.bitmap_table.entries

the fact that we have to access internals of bitmap_table is not nice, but let's refactor it later.

+        bmp_name = dict(name=self.name)
+        # Put the name ahead of the dict

Aha. I don't think that ordering is necessary for json, but why not to order it a bit.

+        bme_dict = {**bmp_name, **fields_dict}

strange to create bmp_name dict just to unpack it. You may as well do

bme_dict = {'name': self.name, **fields_dict}

+        return bme_dict

bme_dict is extra variable: it's created just to return it, so, how about just

return {'name': self.name, **fields_dict}

or, maybe

return {
           'name': self.name,
           'bitmap_table': self.bitmap_table.entries

    class Qcow2BitmapTableEntry(Qcow2Struct):
  @@ -214,6 +230,9 @@ class Qcow2BitmapTableEntry(Qcow2Struct):
              self.type = 'all-zeroes'
  +    def to_dict(self):
+        return dict(type=self.type, offset=self.offset, reserved=self.reserved)

Python has a special syntax for creating dicts :), let's use:

return {'type': self.type, 'offset': self.offset, 'reserved': self.reserved}

    class Qcow2BitmapTable:
  @@ -246,6 +265,9 @@ class QcowHeaderExtension(Qcow2Struct):
              0x44415441: 'Data file'
  +        def to_dict(self):
+            return self.mapping.get(self.value, "<unknown>")

aha, so, actually, to_dict() returns not dict, but string. So it should better be named to_json() (and return any json-dumpable object, like string or dict)

and then, we can add to_json() method to Qcow2BitmapTable as well, to return list.

So, should I refactor it now?


      fields = (
          ('u32', Magic, 'magic'),
          ('u32', '{}', 'length')
@@ -308,6 +330,18 @@ class QcowHeaderExtension(Qcow2Struct):
  +    def to_dict(self):
+        fields_dict = super().to_dict()
+        ext_name = dict(name=self.Magic(self.magic))

strange that we have to create Magic object here... Ok, let's refactor it later

+        # Put the name ahead of the dict
+        he_dict = {**ext_name, **fields_dict}
+        if self.obj is not None:
+            he_dict['data'] = self.obj
+        else:
+            he_dict['data_str'] = self.data_str
+        return he_dict

again, let's avoid extra dict variables:

res = {'name': self.Magic(self.magic), **super().to_dict()}
if ...

      def create(cls, magic, data):
          return QcowHeaderExtension(magic, len(data), data)

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