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dkim=none (message not signed) header.d=none;redhat.com; dmarc=none action=none header.from=virtuozzo.com; Received: from AM7PR08MB5494.eurprd08.prod.outlook.com (2603:10a6:20b:dc::15) by AS8PR08MB6904.eurprd08.prod.outlook.com (2603:10a6:20b:394::23) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4129.27; Fri, 14 May 2021 16:40:06 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133%7]) with mapi id 15.20.4129.026; Fri, 14 May 2021 16:40:06 +0000 Subject: Re: [PATCH v3 3/4] migrate-bitmaps-test: Fix pylint warnings To: Max Reitz , qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, Kevin Wolf References: <20210514154351.629027-1-mreitz@redhat.com> <20210514154351.629027-4-mreitz@redhat.com> From: Vladimir Sementsov-Ogievskiy Message-ID: Date: Fri, 14 May 2021 19:40:04 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 In-Reply-To: <20210514154351.629027-4-mreitz@redhat.com> Content-Type: text/plain; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR02-VE1-obe.outbound.protection.outlook.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 14.05.2021 18:43, Max Reitz wrote: > There are a couple of things pylint takes issue with: > - The "time" import is unused > - The import order (iotests should come last) > - get_bitmap_hash() doesn't use @self and so should be a function > - Semicolons at the end of some lines > - Parentheses after "if" > - Some lines are too long (80 characters instead of 79) > - inject_test_case()'s @name parameter shadows a top-level @name > variable > - "lambda self: mc(self)" were equivalent to just "mc", but in > inject_test_case(), it is not equivalent, so add a comment and disable > the warning locally > - Always put two empty lines after a function > - f'exec: cat > /dev/null' does not need to be an f-string > > Fix them. > > Signed-off-by: Max Reitz > --- [..] > -def inject_test_case(klass, name, method, *args, **kwargs): > +def inject_test_case(klass, suffix, method, *args, **kwargs): > mc = operator.methodcaller(method, *args, **kwargs) > - setattr(klass, 'test_' + method + name, lambda self: mc(self)) > + # The lambda is required to enforce the `self` parameter. Without it, > + # `mc` would be called without any arguments, and then complain. > + # pylint: disable=unnecessary-lambda > + setattr(klass, 'test_' + method + suffix, lambda self: mc(self)) > + > Interesting... I decided to experiment a bit, and what I can say now: The actual reason is that class attrubute of type , becomes a of the class instance on instantiation. lambda is a function, so on instantiation we'll have "method", and method can be called as obj.method(), and original function will get "self" first argument automatically. mc is not a function, it's , so there is no magic, instance of the class doesn't get own method but just a refence to class variable instead. So, let's modify comment to something like: We want to add function attribute to class, so that it correctly converted to method on instantiation. lamba is necessary to "convert" methodcaller object (which is callable, but not a function) to function. with it: Reviewed-by: Vladimir Sementsov-Ogievskiy ==== my expirements ===== # cat x.py import operator class X: def hello(self, arg): print("hello", arg) mc = operator.methodcaller("hello", "Vova") lmd = lambda self: mc(self) print('mc:', type(mc)) print('lmd:', type(lmd)) setattr(X, "test_hello_direct", mc) setattr(X, "test_hello_lambda", lmd) X.simply_assigned = lmd x = X() x.assigned_to_instance = lmd print('mc attached:', type(x.test_hello_direct)) print('lmd attached:', type(x.test_hello_lambda)) print('lmd simply assigned:', type(x.simply_assigned)) print('lmd assigned to instance:', type(x.assigned_to_instance)) x.test_hello_lambda() x.simply_assigned() print("x.test_hello_lambda is x.simply_assigned", x.test_hello_lambda is x.simply_assigned) print("x.test_hello_lambda is X.test_hello_lambda", x.test_hello_lambda is X.test_hello_lambda) print("x.test_hello_direct is X.test_hello_direct", x.test_hello_direct is X.test_hello_direct) print("X.test_hello_lambda is X.simply_assigned", X.test_hello_lambda is X.simply_assigned) print("X.test_hello_lambda type:", type(X.test_hello_lambda)) try: x.assigned_to_instance() except Exception as e: print("assigned to instance call failed:", e) try: x.test_hello_direct() except Exception as e: print("direct call failed:", e) # python3 x.py mc: lmd: mc attached: lmd attached: lmd simply assigned: lmd assigned to instance: hello Vova hello Vova x.test_hello_lambda is x.simply_assigned False x.test_hello_lambda is X.test_hello_lambda False x.test_hello_direct is X.test_hello_direct True X.test_hello_lambda is X.simply_assigned True X.test_hello_lambda type: assigned to instance call failed: () missing 1 required positional argument: 'self' direct call failed: methodcaller expected 1 argument, got 0 -- Best regards, Vladimir