Line break occurred before a binary operator (W503)
Line breaks should occur after the binary operator to keep all variable names aligned.
This rule goes against the PEP 8 recommended style, which was changed on April 16th, 2016 in this commit. The tool will soon be updated to recommend the opposite: line breaks should occur before the binary operator because it keeps all operators aligned.
Anti-pattern
Note: Despite being in the anti-pattern section, this will soon be considered the best practice.
Best practice
Note: Despite being in the best practice section, this will soon be considered an anti-pattern.
Python Code Style Fix Notes
I am working on fixing some of the issues raised by flake8 (a Python Linter) in a Python-based backend repository and thought it would be nice to discuss some of the common issues and the solutions that I gathered from the web (well, mostly StackOverflow). The use of an auto formatter such as black will help resolve some of these common issues automatically. flake8rules is an excellent resource of a complete list of issues as well.
line too long (92 > 79 characters)flake8(E501)
Line too long issues mainly happen for the following cases:
- string
- if-statement
- method chaining
- parameter list
.
I was going to explain with examples how to use Python’s implied line continuation inside parentheses, brackets and braces but decided not to. Nowadays I chose to leave it to my auto formatter to do the job.
For those who insist to write code without any helpful plugins or IDE support, I would like to share that practice does make perfect. I used Vim for a period of writing Java code without autocomplete or format-on-save. I ran style checks and manually fixed issues raised such as having a space between operators. After a month or two, these things became second nature and I was pretty happy with the ability to write well-formatted code without any help. I suppose that was an interesting experience so go ahead and try it yourself.
do not use bare ‘except’flake8(E722)
Exit fullscreen mode
Exit fullscreen mode
Bare except will catch exceptions you almost certainly don’t want to catch, including KeyboardInterrupt (the user hitting Ctrl+C) and Python-raised errors like SystemExit
- Think about what exact exception to catch and specify that instead of just catching any exception.
- Think about whether this exception handling is necessary and are you unintentionally using it for control flow?
- When catching an exception, use either logging or other proper resolutions to handle the anticipated error.
‘from some_package_name_here import *’ used; unable to detect undefined names flake8(F403)
I thought this is an interesting topic for discussion. Earlier in my coding journey, I was amused by the many lines of import statements found in some scripts. Sometimes the number of import statements outweigh the number of practical code within the same file.
Nowadays I know better than to fear abstractions (I still fear BAD abstractions and rightfully so). However, with the help of powerful IDEs, importing and tracing the variable/function to their imported package is easier than before. The problem with ‘from xxx import *’ is that it is unclear what has been imported. Following this, IDEs could not decide whether some of the undefined variables come from the package that you imported or they are errors.
Flake8 r503 python как исправить
Actually, I’m not so much troubled, but I was wondering what everyone was doing and asked a question.
- line break before binary operatorflake8 (W503)
- line break after binary operatorflake8 (W504)
If i follow either one, you will ignore the other rule.
Which is the stronger rule?
Although there is a way of thinking that you can decide which one to protect, you will get lost in spite of what you can do.
I personally like this
The reason is that you can see at a glance that the calculation continues from the previous line without looking beyond the line.
In the first place
If i have an opinion that it is not good to have a line break in the middle of the calculation, I would like to ask you why. . .
Reference site
The tool will soon be updated to recommend the opposite: line breaks should occur before the binary operator because it keeps all operators aligned.
New tool recommended style
PEP8 recommends that you put an operator after a newline, but both are good enough. However, it says that it should be unified to either one (although this is too sticking to consistency . ).
Introduction — pep8-en 1.0 Document Should I start a new line before the binary operator or should I start a new line after it?
Flake8 r503 python как исправить
Flake8-BugBear is a plug-in to find a bug and design problem that may exist in the program. The error code starts with B.
B001: Do not use bare except:, it also catches unexpected events like memory errors, interrupts, system exit, and so on. Prefer except Exception:. If you’re sure what you’re doing, be explicit and write except BaseException:. Disable E722 to avoid duplicate warnings.
B001: Don’t use Bare Except:, it can also capture accidents such as memory errors, interrupts, system exports. Except for exception:. If you are sure what you are doing, then clearly write except Baseexception:. Disable E722 to avoid repeated warnings.
B002: Python does not support the unary prefix increment. Writing ++n is equivalent to +(+(n)), which equals n. You meant n += 1.
B002: Python does not support one yuan prefix increasing. Writing + + n is equal to + ( + (n)), it is equal to n. You mean n + = 1.
B003: Assigning to os.environ doesn’t clear the environment. Subprocesses are going to see outdated variables, in disagreement with the current process. Use os.environ.clear() or the env= argument to Popen.
B003: The task is allocated to Os.envalon and cannot clear the environment. The child process will see outdated variables, which is inconsistent with the current process. Use Os.envalonment.clear () or ENV = parameters for popen.
B004: Using hasattr(x, ‘call’) to test if x is callable is unreliable. If x implements custom getattr or its call is itself not callable, you might get misleading results. Use callable(x) for consistent results.
B004: Use Hasattr (X, ’_ Call _ ‘) to test whether X can be called unreliable. If X implements custom getttr or its call itself cannot be called, you may get the error result. Use the callable (x) to obtain consistent results.
B005: Using .strip() with multi-character strings is misleading the reader. It looks like stripping a substring. Move your character set to a constant if this is deliberate. Use .replace() or regular expressions to remove string fragments.
B005: Use. Strip () with multiple string will mislead readers. It looks like peeling string. If it is intentional, set the character to the constant. use. Replace () or regular expression to delete the string fragment.
B006: Do not use mutable data structures for argument defaults. They are created during function definition time. All calls to the function reuse this one instance of that data structure, persisting changes between them.
B006: Do not use the variable data structure for the default values of the parameter. They are created during functional definition. All calls of this function reuse this instance of the data structure and change the change between them.
B007: Loop control variable not used within the loop body. If this is intended, start the name with an underscore.
B007: The circulating control variable is not used in the cycle body. If this is the case, use the lower line to start named.
B008: Do not perform function calls in argument defaults. The call is performed only once at function definition time. All calls to your function will reuse the result of that definition-time function call. If this is intended, assign the function call to a module-level variable and use that variable as a default value.
B008: Do not execute function calls under the default parameter. Execute only once when the function definitions are executed. All calls of the function will reuse the results of the function call when defining the definition. If this is intentional, then distribute the function to the module -level variable and use the variable as the default value.
B009: Do not call getattr(x, ‘attr’), instead use normal property access: x.attr. Missing a default to getattr will cause an AttributeError to be raised for non-existent properties. There is no additional safety in using getattr if you know the attribute name ahead of time.
B009: Don’t call Getattr (X, ‘ATTR’), but use the normal process account: x.attr. The lack of Getattr’s default values will cause attributes that are not existing to cause Attributeerror. If you know the attribute name in advance, there is no additional security with gettttr.
B010: Do not call setattr(x, ‘attr’, val), instead use normal property access: x.attr = val. There is no additional safety in using setattr if you know the attribute name ahead of time.
B010: Do not call Setattr (x, ‘Attr’, Val), but use the normal process account: x.attr = value. If you know the attribute name in advance, there is no additional security with Setattr.
B011: Do not call assert False since python -O removes these calls. Instead callers should raise AssertionError().
B011: Don’t call assert false, because Python-O will delete these calls. Instead, the caller should trigger Assertioner ().
B012: Use of break, continue or return inside finally blocks will silence exceptions or override return values from the try or except blocks. To silence an exception, do it explicitly in the except block. To properly use a break, continue or return refactor your code so these statements are not in the finally block.
B012: Use Break, Continue or Return Inside Finally Block Will Silence Exceptions or Override Return Value from the Try or Except Blocks. In order to make abnormal silence, this operation is explicitly executed in Except blocks. If you want to use the interruption correctly, continue or return the reconstruction code so that these statements are not in the Finally block.
B013: A length-one tuple literal is redundant. Write except SomeError: instead of except (SomeError,):.
B013: Length-One Tuple Little is redundant.
B014: Redundant exception types in except (Exception, TypeError):. Write except Exception:, which catches exactly the same exceptions.
B014: Redundant Exception Types in Except (Exception, Typerror):. Write Except:, it captures exactly the same abnormality.
B015: Pointless comparison. This comparison does nothing but waste CPU instructions. Either prepend assert or remove it.
B015: meaningless comparison. This comparison will only waste the CPU instructions. Either supplement the assertion or delete it.
B016: Cannot raise a literal. Did you intend to return it or raise an Exception?
Do not increase a facial value. Do you plan to return it or increase an exceptional value?
B017: self.assertRaises(Exception): should be considered evil. It can lead to your test passing even if the code being tested is never executed due to a typo. Either assert for a more specific exception (builtin or custom), use assertRaisesRegex, or use the context manager form of assertRaises (with self.assertRaises(Exception) as ex:) with an assertion against the data available in ex.
B017: Self.assertraises (exception): It should be regarded as evil. It can cause your test to pass, even if the test code is never performed due to errors. Either an assertion for more specific abnormalities (built -in or customized), use AssertraisesRegex, or use Assertraises’s context manager form (using Self.asSerTraises (Exception) as EX :), to assert the data available in EX.
B018: Found useless expression. Either assign it to a variable or remove it.
B018: Find a useless expression. Either assign it to the variable or delete it.
B019: Use of functools.lru_cache or functools.cache on methods can lead to memory leaks. The cache may retain instance references, preventing garbage collection.
B019: The method of using Functools.lru cache or functools.cache can cause memory leakage. The cache may retain instance reference to prevent garbage recycling.
B020: Loop control variable overrides iterable it iterates
020: Circulation/control variable/code rewriting iteration
B021: f-string used as docstring. This will be interpreted by python as a joined string rather than a docstring.
B021: F-String is used as a document string. This is interpreted by Python as a connection string, not a document string.
B022: No arguments passed to contextlib.suppress. No exceptions will be suppressed and therefore this context manager is redundant. N.B. this rule currently does not flag suppress calls to avoid potential false positives due to similarly named user-defined functions.
B022: No parameters passed to contextLib.suppress. It will not inhibit any abnormalities, so the context is redundant. Note that this rule does not marked inhibitory calls at present, to avoid potential misunderstanding caused by user -like user -defined functions.
The following warnings are disabled by default because they are controversial. They may or may not apply to you, enable them explicitly in your configuration if you find them useful. Read below on how to enable.
The following warnings are banned by default because they are controversial. They may be applicable to you or you may not apply to you. If you think they are useful, please explicitly enable them in your configuration. Read the following about how to enable.
B901: Using return x in a generator function used to be syntactically invalid in Python 2. In Python 3 return x can be used in a generator as a return value in conjunction with yield from. Users coming from Python 2 may expect the old behavior which might lead to bugs. Use native async def coroutines or mark intentional return x usage with # noqa on the same line.
B901: The use of Return X in the generator function was invalid in Python 2. In Python 3, X can be used in the generator as a return value that binds yield. Users from Python2 may expect old behaviors to cause bugs. Use local asynchronous definition collaborative programs or marked X usage and # noqa in the same row.
B902: Invalid first argument used for method. Use self for instance methods, and cls for class methods (which includes new and init_subclass) or instance methods of metaclasses (detected as classes directly inheriting from type).
B902: The first parameter used by the method is invalid. Use SELF for the instance method (including _ new _ and _ init _ subclass _) or the instance method of the meta -class (as a class test directly inherited by type).
B903: Use collections.namedtuple (or typing.NamedTuple) for data classes that only set attributes in an init method, and do nothing else. If the attributes should be mutable, define the attributes in slots to save per-instance memory and to prevent accidentally creating additional attributes on instances.
B903: Use Collections.Namedtuple. Set attributes only in _ init _ medhod without doing other things, you can use namedtuple). If the attribute should be variable, define attributes in _ slots _ _ in order to save the memory of each instance and prevent accidental creation of other attributes on the instance.
B904: Within an except clause, raise exceptions with raise … from err or raise … from None to distinguish them from errors in exception handling. See the exception chaining tutorial for details.
B904: In Except clauses, use RAISE… From Err or Raise… from None to distinguish errors in abnormal processing. For details, please refer to the abnormal chain tutorial.
B950: Line too long. This is a pragmatic equivalent of pycodestyle’s E501: it considers “max-line-length” but only triggers when the value has been exceeded by more than 10%. You will no longer be forced to reformat code due to the closing parenthesis being one character too far to satisfy the linter. At the same time, if you do significantly violate the line length, you will receive a message that states what the actual limit is. This is inspired by Raymond Hettinger’s “Beyond PEP 8” talk and highway patrol not stopping you if you drive < 5mph too fast. Disable E501 to avoid duplicate warnings. Like E501, this error ignores long shebangs on the first line and urls or paths that are on their own line:
B950: The team is too long. This is a practical PyCodeStyle E501 equivalent: it considers "MAX-LINE-LENGTH", but only triggers when the value exceeds 10%. You will no longer be forced to format the code, because the end of the bracket is too far to meet the temporary. At the same time, if you really violate the length of the line, then you will receive a message to explain what the actual limit is. This inspiration comes from Raymond Hinger’s "Beyond PEP 8" speech and highway patrol police will not stop you, if you drive more than 5 miles per hour. Disable E501 to avoid repeated warnings. Like E501, this error ignores the shebangs on the first line, and the URL or path on their own:
To enable Bugbear’s opinionated checks (B9xx), specify an —extend-select command-line option or extend-select= option in your config file (requires flake8 >=4.0):
To enable BugBear’s OPINIONATED Checks (B9XX), specify in the configuration file-Extend-SELECT command line options or extend-select = option (required Flake8> = 4.0):
E error at the beginning
Flake8-comprehensions is a plug-in
C400-402: Unnecessary generator — rewrite as a <list/set/dict> comprehension.
It’s unnecessary to use list, set, or dict around a generator expression, since there are equivalent comprehensions for these types. For example:
Rewrite list(f(x) for x in foo) as [f(x) for x in foo]
Rewrite set(f(x) for x in foo) as
Rewrite dict((x, f(x)) for x in foo) as
C403-404: Unnecessary list comprehension — rewrite as a <set/dict> comprehension.
It’s unnecessary to use a list comprehension inside a call to set or dict, since there are equivalent comprehensions for these types. For example:
Rewrite set([f(x) for x in foo]) as
Rewrite dict([(x, f(x)) for x in foo]) as
C405-406: Unnecessary <list/tuple> literal — rewrite as a <set/dict> literal.
It’s unnecessary to use a list or tuple literal within a call to set or dict. For example:
Rewrite set([1, 2]) as <1, 2>
Rewrite set((1, 2)) as <1, 2>
Rewrite set([]) as set()
Rewrite dict([(1, 2)]) as <1: 2>
Rewrite dict(((1, 2),)) as <1: 2>
Rewrite dict([]) as <>
C408: Unnecessary <dict/list/tuple> call — rewrite as a literal.
It’s slower to call e.g. dict() than using the empty literal, because the name dict must be looked up in the global scope in case it has been rebound. Same for the other two basic types here. For example:
Rewrite dict() as <>
Rewrite dict(a=1, b=2) as <“a”: 1, “b”: 2>
Rewrite list() as []
Rewrite tuple() as ()
C409-410: Unnecessary <list/tuple> passed to <list/tuple>() — (remove the outer call to <list/tuple> ()/rewrite as a <list/tuple> literal).
It’s unnecessary to use a list or tuple literal within a call to list or tuple, since there is literal syntax for these types. For example:
Rewrite tuple([1, 2]) as (1, 2)
Rewrite tuple((1, 2)) as (1, 2)
Rewrite tuple([]) as ()
Rewrite list([1, 2]) as [1, 2]
Rewrite list((1, 2)) as [1, 2]
Rewrite list([]) as []
C411: Unnecessary list call — remove the outer call to list().
It’s unnecessary to use a list around a list comprehension, since it is equivalent without it. For example:
Rewrite list([f(x) for x in foo]) as [f(x) for x in foo]
C413: Unnecessary <list/reversed> call around sorted().
It’s unnecessary to use list() around sorted() as it already returns a list. It is also unnecessary to use reversed() around sorted() as the latter has a reverse argument. For example:
Rewrite list(sorted([2, 3, 1])) as sorted([2, 3, 1])
Rewrite reversed(sorted([2, 3, 1])) as sorted([2, 3, 1], reverse=True)
Rewrite reversed(sorted([2, 3, 1], reverse=True)) as sorted([2, 3, 1])
C414: Unnecessary <list/reversed/set/sorted/tuple> call within <list/set/sorted/tuple>().
It’s unnecessary to double-cast or double-process iterables by wrapping the listed functions within list/set/sorted/tuple. For example:
Rewrite list(list(iterable)) as list(iterable)
Rewrite list(tuple(iterable)) as list(iterable)
Rewrite tuple(list(iterable)) as tuple(iterable)
Rewrite tuple(tuple(iterable)) as tuple(iterable)
Rewrite set(set(iterable)) as set(iterable)
Rewrite set(list(iterable)) as set(iterable)
Rewrite set(tuple(iterable)) as set(iterable)
Rewrite set(sorted(iterable)) as set(iterable)
Rewrite set(reversed(iterable)) as set(iterable)
Rewrite sorted(list(iterable)) as sorted(iterable)
Rewrite sorted(tuple(iterable)) as sorted(iterable)
Rewrite sorted(sorted(iterable)) as sorted(iterable)
Rewrite sorted(reversed(iterable)) as sorted(iterable)
C415: Unnecessary subscript reversal of iterable within <reversed/set/sorted>().
It’s unnecessary to reverse the order of an iterable when passing it into one of the listed functions will change the order again. For example:
Rewrite set(iterable[::-1]) as set(iterable)
Rewrite sorted(iterable)[::-1] as sorted(iterable, reverse=True)
Rewrite reversed(iterable[::-1]) as iterable
C416: Unnecessary <list/set> comprehension — rewrite using <list/set>().
It’s unnecessary to use a list comprehension if the elements are unchanged. The iterable should be wrapped in list() or set() instead. For example:
Rewrite [x for x in iterable] as list(iterable)
Rewrite
Error at the beginning of SIM
SIM101: Multiple isinstance-calls which can be merged into a single call by using a tuple as a second argument (example)
SIM104 : Use ‘yield from iterable’ (introduced in Python 3.3, see PEP 380) (example)
SIM105: Use ‘contextlib.suppress(…)’ instead of try-except-pass (example)
SIM107: Don’t use return in try/except and finally (example)
SIM108: Use the ternary operator if it’s reasonable (example)
SIM109: Use a tuple to compare a value against multiple values (example)
SIM110: Use any(…) (example)
SIM111: Use all(…) (example)
SIM113: Use enumerate instead of manually incrementing a counter (example)
SIM114: Combine conditions via a logical or to prevent duplicating code (example)
SIM115: Use context handler for opening files (example)
SIM116: Use a dictionary instead of many if/else equality checks (example)
SIM117: Merge with-statements that use the same scope (example)
SIM119: Moved to flake8-scream due to issue 63
SIM120 : Use ‘class FooBar:’ instead of ‘class FooBar(object):’ (example)
SIM121: Reserved for SIM908 once it’s stable
SIM125: Reserved for SIM905 once it’s stable
SIM126: Reserved for SIM906 once it’s stable
SIM127: Reserved for SIM907 once it’s stable
Simplifying Comparations:
SIM201: Use ‘a != b’ instead of ‘not a == b’ (example)
SIM202: Use ‘a == b’ instead of ‘not a != b’ (example)
SIM203: Use ‘a not in b’ instead of ‘not (a in b)’ (example)
SIM204: Moved to flake8-scream due to issue 116
SIM205: Moved to flake8-scream due to issue 116
SIM206: Moved to flake8-scream due to issue 116
SIM207: Moved to flake8-scream due to issue 116
SIM208: Use ‘a’ instead of ‘not (not a)’ (example)
SIM210: Use ‘bool(a)’ instead of ‘True if a else False’ (example)
SIM211: Use ‘not a’ instead of ‘False if a else True’ (example)
SIM212: Use ‘a if a else b’ instead of ‘b if not a else a’ (example)
SIM220: Use ‘False’ instead of ‘a and not a’ (example)
SIM221: Use ‘True’ instead of ‘a or not a’ (example)
SIM222: Use ‘True’ instead of ‘… or True’ (example)
SIM223: Use ‘False’ instead of ‘… and False’ (example)
SIM224: Reserved for SIM901 once it’s stable
SIM300: Use ‘age == 42’ instead of ‘42 == age’ (example)
Simplifying usage of dictionaries:
SIM401: Use ‘a_dict.get(key, “default_value”)’ instead of an if-block (example)
SIM118: Use ‘key in dict’ instead of ‘key in dict.keys()’ (example)
General Code Style:
SIM102: Use a single if-statement instead of nested if-statements (example)
SIM103: Return the boolean condition directly (example)
SIM106: Handle error-cases first (example). This rule was removed due to too many false-positives.
SIM112: Use CAPITAL environment variables (example)
SIM122 / SIM902: Moved to flake8-scream due to issue 125
SIM123 / SIM902: Moved to flake8-scream due to issue 130
SIM124: Reserved for SIM909 once it’s stable
Experimental rules:
Getting rules right for every possible case is hard. I don’t want to disturb peoples workflows. For this reason, flake8-simplify introduces new rules with the SIM9 prefix. Every new rule will start with SIM9 and stay there for at least 6 months. In this time people can give feedback. Once the rule is stable, the code will change to another number.