Pep8 is a tool to check your Python code against some of the style conventions in PEP 8. Text from PEP 8: $ pep8 --show-source --show-pep8.
This document gives coding conventions for the Python code comprising the standard library in the main Python distribution. Please see the companion informational PEP describing style guidelines for the C code in the C implementation of Python. This document and (Docstring Conventions) were adapted from Guido's original Python Style Guide essay, with some additions from Barry's style guide.
This style guide evolves over time as additional conventions are identified and past conventions are rendered obsolete by changes in the language itself. Many projects have their own coding style guidelines.
In the event of any conflicts, such project-specific guides take precedence for that project. One of Guido's key insights is that code is read much more often than it is written. The guidelines provided here are intended to improve the readability of code and make it consistent across the wide spectrum of Python code. As says, 'Readability counts'. A style guide is about consistency.
Consistency with this style guide is important. Consistency within a project is more important. Consistency within one module or function is the most important. However, know when to be inconsistent - sometimes style guide recommendations just aren't applicable. When in doubt, use your best judgment.
Look at other examples and decide what looks best. And don't hesitate to ask! In particular: do not break backwards compatibility just to comply with this PEP! Some other good reasons to ignore a particular guideline:. When applying the guideline would make the code less readable, even for someone who is used to reading code that follows this PEP. To be consistent with surrounding code that also breaks it (maybe for historic reasons) - although this is also an opportunity to clean up someone else's mess (in true XP style). Because the code in question predates the introduction of the guideline and there is no other reason to be modifying that code.
When the code needs to remain compatible with older versions of Python that don't support the feature recommended by the style guide. Use 4 spaces per indentation level. Continuation lines should align wrapped elements either vertically using Python's implicit line joining inside parentheses, brackets and braces, or using a hanging indent. When using a hanging indent the following should be considered; there should be no arguments on the first line and further indentation should be used to clearly distinguish itself as a continuation line. Yes: # Aligned with opening delimiter. Foo = longfunctionname(varone, vartwo, varthree, varfour) # More indentation included to distinguish this from the rest. Def longfunctionname( varone, vartwo, varthree, varfour): print(varone) # Hanging indents should add a level.
Foo = longfunctionname( varone, vartwo, varthree, varfour) No: # Arguments on first line forbidden when not using vertical alignment. Foo = longfunctionname(varone, vartwo, varthree, varfour) # Further indentation required as indentation is not distinguishable. Def longfunctionname( varone, vartwo, varthree, varfour): print(varone) The 4-space rule is optional for continuation lines. Optional: # Hanging indents.may. be indented to other than 4 spaces. Foo = longfunctionname( varone, vartwo, varthree, varfour) When the conditional part of an if-statement is long enough to require that it be written across multiple lines, it's worth noting that the combination of a two character keyword (i.e. If), plus a single space, plus an opening parenthesis creates a natural 4-space indent for the subsequent lines of the multiline conditional.
This can produce a visual conflict with the indented suite of code nested inside the if-statement, which would also naturally be indented to 4 spaces. This PEP takes no explicit position on how (or whether) to further visually distinguish such conditional lines from the nested suite inside the if-statement. Acceptable options in this situation include, but are not limited to: # No extra indentation. If (thisisonething and thatisanotherthing): dosomething # Add a comment, which will provide some distinction in editors # supporting syntax highlighting. If (thisisonething and thatisanotherthing): # Since both conditions are true, we can frobnicate.
Dosomething # Add some extra indentation on the conditional continuation line. Spaces are the preferred indentation method. Tabs should be used solely to remain consistent with code that is already indented with tabs.
Python 3 disallows mixing the use of tabs and spaces for indentation. Python 2 code indented with a mixture of tabs and spaces should be converted to using spaces exclusively. When invoking the Python 2 command line interpreter with the -t option, it issues warnings about code that illegally mixes tabs and spaces. When using -tt these warnings become errors.
These options are highly recommended! Limit all lines to a maximum of 79 characters.
For flowing long blocks of text with fewer structural restrictions (docstrings or comments), the line length should be limited to 72 characters. Limiting the required editor window width makes it possible to have several files open side-by-side, and works well when using code review tools that present the two versions in adjacent columns. The default wrapping in most tools disrupts the visual structure of the code, making it more difficult to understand. The limits are chosen to avoid wrapping in editors with the window width set to 80, even if the tool places a marker glyph in the final column when wrapping lines. Some web based tools may not offer dynamic line wrapping at all. Some teams strongly prefer a longer line length.
For code maintained exclusively or primarily by a team that can reach agreement on this issue, it is okay to increase the nominal line length from 80 to 100 characters (effectively increasing the maximum length to 99 characters), provided that comments and docstrings are still wrapped at 72 characters. The Python standard library is conservative and requires limiting lines to 79 characters (and docstrings/comments to 72). The preferred way of wrapping long lines is by using Python's implied line continuation inside parentheses, brackets and braces. Long lines can be broken over multiple lines by wrapping expressions in parentheses.
These should be used in preference to using a backslash for line continuation. Backslashes may still be appropriate at times.
For example, long, multiple with-statements cannot use implicit continuation, so backslashes are acceptable: with open('/path/to/some/file/you/want/to/read') as file1, open('/path/to/some/file/being/written', 'w') as file2: file2.write(file1.read) (See the previous discussion on for further thoughts on the indentation of such multiline with-statements.) Another such case is with assert statements. Make sure to indent the continued line appropriately. For decades the recommended style was to break after binary operators. But this can hurt readability in two ways: the operators tend to get scattered across different columns on the screen, and each operator is moved away from its operand and onto the previous line. Here, the eye has to do extra work to tell which items are added and which are subtracted: # No: operators sit far away from their operands income = (grosswages + taxableinterest + (dividends - qualifieddividends) - iradeduction - studentloaninterest) To solve this readability problem, mathematicians and their publishers follow the opposite convention.
Donald Knuth explains the traditional rule in his Computers and Typesetting series: 'Although formulas within a paragraph always break after binary operations and relations, displayed formulas always break before binary operations'. Following the tradition from mathematics usually results in more readable code: # Yes: easy to match operators with operands income = (grosswages + taxableinterest + (dividends - qualifieddividends) - iradeduction - studentloaninterest) In Python code, it is permissible to break before or after a binary operator, as long as the convention is consistent locally. For new code Knuth's style is suggested. Surround top-level function and class definitions with two blank lines. Method definitions inside a class are surrounded by a single blank line.
Extra blank lines may be used (sparingly) to separate groups of related functions. Blank lines may be omitted between a bunch of related one-liners (e.g. A set of dummy implementations). Use blank lines in functions, sparingly, to indicate logical sections. Python accepts the control-L (i.e.
^L) form feed character as whitespace; Many tools treat these characters as page separators, so you may use them to separate pages of related sections of your file. Note, some editors and web-based code viewers may not recognize control-L as a form feed and will show another glyph in its place. Code in the core Python distribution should always use UTF-8 (or ASCII in Python 2). Files using ASCII (in Python 2) or UTF-8 (in Python 3) should not have an encoding declaration.
In the standard library, non-default encodings should be used only for test purposes or when a comment or docstring needs to mention an author name that contains non-ASCII characters; otherwise, using x, u, U, or N escapes is the preferred way to include non-ASCII data in string literals. For Python 3.0 and beyond, the following policy is prescribed for the standard library (see ): All identifiers in the Python standard library MUST use ASCII-only identifiers, and SHOULD use English words wherever feasible (in many cases, abbreviations and technical terms are used which aren't English). In addition, string literals and comments must also be in ASCII. The only exceptions are (a) test cases testing the non-ASCII features, and (b) names of authors. Authors whose names are not based on the Latin alphabet (latin-1, ISO/IEC 8859-1 character set) MUST provide a transliteration of their names in this character set. Open source projects with a global audience are encouraged to adopt a similar policy. Imports should usually be on separate lines: Yes: import os import sys No: import sys, os It's okay to say this though: from subprocess import Popen, PIPE.
Imports are always put at the top of the file, just after any module comments and docstrings, and before module globals and constants. Imports should be grouped in the following order:.
Standard library imports. Related third party imports. Local application/library specific imports. You should put a blank line between each group of imports.
Absolute imports are recommended, as they are usually more readable and tend to be better behaved (or at least give better error messages) if the import system is incorrectly configured (such as when a directory inside a package ends up on sys.path): import mypkg.sibling from mypkg import sibling from mypkg.sibling import example However, explicit relative imports are an acceptable alternative to absolute imports, especially when dealing with complex package layouts where using absolute imports would be unnecessarily verbose: from. Import sibling from.sibling import example Standard library code should avoid complex package layouts and always use absolute imports. Implicit relative imports should never be used and have been removed in Python 3. When importing a class from a class-containing module, it's usually okay to spell this: from myclass import MyClass from foo.bar.yourclass import YourClass If this spelling causes local name clashes, then spell them explicitly: import myclass import foo.bar.yourclass and use 'myclass.MyClass' and 'foo.bar.yourclass.YourClass'.
Wildcard imports ( from import.) should be avoided, as they make it unclear which names are present in the namespace, confusing both readers and many automated tools. There is one defensible use case for a wildcard import, which is to republish an internal interface as part of a public API (for example, overwriting a pure Python implementation of an interface with the definitions from an optional accelerator module and exactly which definitions will be overwritten isn't known in advance). When republishing names this way, the guidelines below regarding public and internal interfaces still apply. Module level 'dunders' (i.e. Names with two leading and two trailing underscores) such as all, author, version, etc.
Should be placed after the module docstring but before any import statements except from future imports. Python mandates that future-imports must appear in the module before any other code except docstrings: 'This is the example module.
This module does stuff. ' from future import barryasFLUFL all = 'a', 'b', 'c' version = '0.1' author = 'Cardinal Biggles' import os import sys. Avoid trailing whitespace anywhere. Because it's usually invisible, it can be confusing: e.g. A backslash followed by a space and a newline does not count as a line continuation marker.
Some editors don't preserve it and many projects (like CPython itself) have pre-commit hooks that reject it. Always surround these binary operators with a single space on either side: assignment ( =), augmented assignment ( +=, -= etc.), comparisons ( ,!=, =, in, not in, is, is not), Booleans ( and, or, not). If operators with different priorities are used, consider adding whitespace around the operators with the lowest priority(ies). Use your own judgment; however, never use more than one space, and always have the same amount of whitespace on both sides of a binary operator.
Yes: i = i + 1 submitted += 1 x = x.2 - 1 hypot2 = x.x + y.y c = (a+b). (a-b) No: i=i+1 submitted +=1 x = x. 2 - 1 hypot2 = x. x + y.
y c = (a + b). (a - b). Don't use spaces around the = sign when used to indicate a keyword argument or a default parameter value. Yes: def complex(real, imag=0.0): return magic(r=real, i=imag) No: def complex(real, imag = 0.0): return magic(r = real, i = imag). Function annotations should use the normal rules for colons and always have spaces around the - arrow if present. (See below for more about function annotations.) Yes: def munge(input: AnyStr).
Def munge - AnyStr. No: def munge(input:AnyStr). Def munge-PosInt. When combining an argument annotation with a default value, use spaces around the = sign (but only for those arguments that have both an annotation and a default).
Yes: def munge(sep: AnyStr = None). Def munge(input: AnyStr, sep: AnyStr = None, limit=1000).
No: def munge(input: AnyStr=None). Def munge(input: AnyStr, limit = 1000). Compound statements (multiple statements on the same line) are generally discouraged. Yes: if foo 'blah': doblahthing doone dotwo dothree Rather not: if foo 'blah': doblahthing doone; dotwo; dothree. While sometimes it's okay to put an if/for/while with a small body on the same line, never do this for multi-clause statements.
Also avoid folding such long lines! Rather not: if foo 'blah': doblahthing for x in lst: total += x while t. Trailing commas are usually optional, except they are mandatory when making a tuple of one element (and in Python 2 they have semantics for the print statement).
For clarity, it is recommended to surround the latter in (technically redundant) parentheses. Yes: FILES = ('setup.cfg',) OK, but confusing: FILES = 'setup.cfg', When trailing commas are redundant, they are often helpful when a version control system is used, when a list of values, arguments or imported items is expected to be extended over time. The pattern is to put each value (etc.) on a line by itself, always adding a trailing comma, and add the close parenthesis/bracket/brace on the next line. However it does not make sense to have a trailing comma on the same line as the closing delimiter (except in the above case of singleton tuples). Yes: FILES = 'setup.cfg', 'tox.ini'initialize(FILES, error=True, ) No: FILES = 'setup.cfg', 'tox.ini', initialize(FILES, error=True,). Comments that contradict the code are worse than no comments. Always make a priority of keeping the comments up-to-date when the code changes!
Comments should be complete sentences. The first word should be capitalized, unless it is an identifier that begins with a lower case letter (never alter the case of identifiers!). Block comments generally consist of one or more paragraphs built out of complete sentences, with each sentence ending in a period. You should use two spaces after a sentence-ending period in multi- sentence comments, except after the final sentence. When writing English, follow Strunk and White. Python coders from non-English speaking countries: please write your comments in English, unless you are 120% sure that the code will never be read by people who don't speak your language. Conventions for writing good documentation strings (a.k.a.
'docstrings') are immortalized in. Write docstrings for all public modules, functions, classes, and methods. Docstrings are not necessary for non-public methods, but you should have a comment that describes what the method does. This comment should appear after the def line. describes good docstring conventions. Note that most importantly, the ' that ends a multiline docstring should be on a line by itself: 'Return a foobang Optional plotz says to frobnicate the bizbaz first.
'. For one liner docstrings, please keep the closing ' on the same line. There are a lot of different naming styles. It helps to be able to recognize what naming style is being used, independently from what they are used for. The following naming styles are commonly distinguished:. b (single lowercase letter). B (single uppercase letter).
lowercase. lowercasewithunderscores. UPPERCASE. UPPERCASEWITHUNDERSCORES.
CapitalizedWords (or CapWords, or CamelCase - so named because of the bumpy look of its letters ). This is also sometimes known as StudlyCaps. Note: When using acronyms in CapWords, capitalize all the letters of the acronym.
Thus HTTPServerError is better than HttpServerError. mixedCase (differs from CapitalizedWords by initial lowercase character!). CapitalizedWordsWithUnderscores (ugly!) There's also the style of using a short unique prefix to group related names together.
This is not used much in Python, but it is mentioned for completeness. For example, the os.stat function returns a tuple whose items traditionally have names like stmode, stsize, stmtime and so on. (This is done to emphasize the correspondence with the fields of the POSIX system call struct, which helps programmers familiar with that.) The X11 library uses a leading X for all its public functions. In Python, this style is generally deemed unnecessary because attribute and method names are prefixed with an object, and function names are prefixed with a module name.
In addition, the following special forms using leading or trailing underscores are recognized (these can generally be combined with any case convention):. singleleadingunderscore: weak 'internal use' indicator.
From M import. does not import objects whose name starts with an underscore. singletrailingunderscore: used by convention to avoid conflicts with Python keyword, e.g.
Tkinter.Toplevel(master, class='ClassName'). doubleleadingunderscore: when naming a class attribute, invokes name mangling (inside class FooBar, boo becomes FooBarboo; see below). doubleleadingandtrailingunderscore: 'magic' objects or attributes that live in user-controlled namespaces. init, import or file.
Never invent such names; only use them as documented. Use the function naming rules: lowercase with words separated by underscores as necessary to improve readability. Use one leading underscore only for non-public methods and instance variables. To avoid name clashes with subclasses, use two leading underscores to invoke Python's name mangling rules. Python mangles these names with the class name: if class Foo has an attribute named a, it cannot be accessed by Foo.a. (An insistent user could still gain access by calling Foo.Fooa.) Generally, double leading underscores should be used only to avoid name conflicts with attributes in classes designed to be subclassed.
Note: there is some controversy about the use of names (see below). Always decide whether a class's methods and instance variables (collectively: 'attributes') should be public or non-public. If in doubt, choose non-public; it's easier to make it public later than to make a public attribute non-public. Public attributes are those that you expect unrelated clients of your class to use, with your commitment to avoid backwards incompatible changes. Non-public attributes are those that are not intended to be used by third parties; you make no guarantees that non-public attributes won't change or even be removed. We don't use the term 'private' here, since no attribute is really private in Python (without a generally unnecessary amount of work). Another category of attributes are those that are part of the 'subclass API' (often called 'protected' in other languages).
Some classes are designed to be inherited from, either to extend or modify aspects of the class's behavior. When designing such a class, take care to make explicit decisions about which attributes are public, which are part of the subclass API, and which are truly only to be used by your base class.
With this in mind, here are the Pythonic guidelines:. Public attributes should have no leading underscores.
If your public attribute name collides with a reserved keyword, append a single trailing underscore to your attribute name. This is preferable to an abbreviation or corrupted spelling. (However, notwithstanding this rule, 'cls' is the preferred spelling for any variable or argument which is known to be a class, especially the first argument to a class method.) Note 1: See the argument name recommendation above for class methods. For simple public data attributes, it is best to expose just the attribute name, without complicated accessor/mutator methods. Keep in mind that Python provides an easy path to future enhancement, should you find that a simple data attribute needs to grow functional behavior. In that case, use properties to hide functional implementation behind simple data attribute access syntax.
Note 1: Properties only work on new-style classes. Note 2: Try to keep the functional behavior side-effect free, although side-effects such as caching are generally fine. Note 3: Avoid using properties for computationally expensive operations; the attribute notation makes the caller believe that access is (relatively) cheap. If your class is intended to be subclassed, and you have attributes that you do not want subclasses to use, consider naming them with double leading underscores and no trailing underscores. This invokes Python's name mangling algorithm, where the name of the class is mangled into the attribute name. This helps avoid attribute name collisions should subclasses inadvertently contain attributes with the same name.
Note 1: Note that only the simple class name is used in the mangled name, so if a subclass chooses both the same class name and attribute name, you can still get name collisions. Note 2: Name mangling can make certain uses, such as debugging and getattr, less convenient. However the name mangling algorithm is well documented and easy to perform manually.
Note 3: Not everyone likes name mangling. Try to balance the need to avoid accidental name clashes with potential use by advanced callers. Any backwards compatibility guarantees apply only to public interfaces. Accordingly, it is important that users be able to clearly distinguish between public and internal interfaces.
Documented interfaces are considered public, unless the documentation explicitly declares them to be provisional or internal interfaces exempt from the usual backwards compatibility guarantees. All undocumented interfaces should be assumed to be internal. To better support introspection, modules should explicitly declare the names in their public API using the all attribute. Setting all to an empty list indicates that the module has no public API. Even with all set appropriately, internal interfaces (packages, modules, classes, functions, attributes or other names) should still be prefixed with a single leading underscore.
An interface is also considered internal if any containing namespace (package, module or class) is considered internal. Imported names should always be considered an implementation detail. Other modules must not rely on indirect access to such imported names unless they are an explicitly documented part of the containing module's API, such as os.path or a package's init module that exposes functionality from submodules.
Code should be written in a way that does not disadvantage other implementations of Python (PyPy, Jython, IronPython, Cython, Psyco, and such). For example, do not rely on CPython's efficient implementation of in-place string concatenation for statements in the form a += b or a = a + b. This optimization is fragile even in CPython (it only works for some types) and isn't present at all in implementations that don't use refcounting. In performance sensitive parts of the library, the '.join form should be used instead.
This will ensure that concatenation occurs in linear time across various implementations. Comparisons to singletons like None should always be done with is or is not, never the equality operators.
Also, beware of writing if x when you really mean if x is not None - e.g. When testing whether a variable or argument that defaults to None was set to some other value. The other value might have a type (such as a container) that could be false in a boolean context!. Use is not operator rather than not. While both expressions are functionally identical, the former is more readable and preferred. Yes: if foo is not None: No: if not foo is None:.
When implementing ordering operations with rich comparisons, it is best to implement all six operations ( eq, ne, lt, le, gt, ge) rather than relying on other code to only exercise a particular comparison. To minimize the effort involved, the functools.totalordering decorator provides a tool to generate missing comparison methods. Indicates that reflexivity rules are assumed by Python. Thus, the interpreter may swap y x with x = x with x operator.
However, it is best to implement all six operations so that confusion doesn't arise in other contexts. Always use a def statement instead of an assignment statement that binds a lambda expression directly to an identifier. Yes: def f(x): return 2.x No: f = lambda x: 2.x The first form means that the name of the resulting function object is specifically 'f' instead of the generic '. This is more useful for tracebacks and string representations in general. The use of the assignment statement eliminates the sole benefit a lambda expression can offer over an explicit def statement (i.e.
That it can be embedded inside a larger expression). Derive exceptions from Exception rather than BaseException. Direct inheritance from BaseException is reserved for exceptions where catching them is almost always the wrong thing to do. Design exception hierarchies based on the distinctions that code catching the exceptions is likely to need, rather than the locations where the exceptions are raised. Aim to answer the question 'What went wrong?' Programmatically, rather than only stating that 'A problem occurred' (see for an example of this lesson being learned for the builtin exception hierarchy) Class naming conventions apply here, although you should add the suffix 'Error' to your exception classes if the exception is an error. Non-error exceptions that are used for non-local flow control or other forms of signaling need no special suffix.
Use exception chaining appropriately. In Python 3, 'raise X from Y' should be used to indicate explicit replacement without losing the original traceback. When deliberately replacing an inner exception (using 'raise X' in Python 2 or 'raise X from None' in Python 3.3+), ensure that relevant details are transferred to the new exception (such as preserving the attribute name when converting KeyError to AttributeError, or embedding the text of the original exception in the new exception message). When raising an exception in Python 2, use raise ValueError('message') instead of the older form raise ValueError, 'message'.
The latter form is not legal Python 3 syntax. The paren-using form also means that when the exception arguments are long or include string formatting, you don't need to use line continuation characters thanks to the containing parentheses. When catching exceptions, mention specific exceptions whenever possible instead of using a bare except: clause: try: import platformspecificmodule except ImportError: platformspecificmodule = None A bare except: clause will catch SystemExit and KeyboardInterrupt exceptions, making it harder to interrupt a program with Control-C, and can disguise other problems. If you want to catch all exceptions that signal program errors, use except Exception: (bare except is equivalent to except BaseException:).
A good rule of thumb is to limit use of bare 'except' clauses to two cases:. If the exception handler will be printing out or logging the traceback; at least the user will be aware that an error has occurred.
If the code needs to do some cleanup work, but then lets the exception propagate upwards with raise. Try.finally can be a better way to handle this case.
When binding caught exceptions to a name, prefer the explicit name binding syntax added in Python 2.6: try: processdata except Exception as exc: raise DataProcessingFailedError(str(exc)) This is the only syntax supported in Python 3, and avoids the ambiguity problems associated with the older comma-based syntax. When catching operating system errors, prefer the explicit exception hierarchy introduced in Python 3.3 over introspection of errno values. Additionally, for all try/except clauses, limit the try clause to the absolute minimum amount of code necessary.
Again, this avoids masking bugs. Yes: try: value = collectionkey except KeyError: return keynotfound(key) else: return handlevalue(value) No: try: # Too broad! Return handlevalue(collectionkey) except KeyError: # Will also catch KeyError raised by handlevalue return keynotfound(key). When a resource is local to a particular section of code, use a with statement to ensure it is cleaned up promptly and reliably after use. A try/finally statement is also acceptable. Context managers should be invoked through separate functions or methods whenever they do something other than acquire and release resources. Yes: with conn.begintransaction: dostuffintransaction(conn) No: with conn: dostuffintransaction(conn) The latter example doesn't provide any information to indicate that the enter and exit methods are doing something other than closing the connection after a transaction.
Being explicit is important in this case. Be consistent in return statements. Either all return statements in a function should return an expression, or none of them should. If any return statement returns an expression, any return statements where no value is returned should explicitly state this as return None, and an explicit return statement should be present at the end of the function (if reachable). Yes: def foo(x): if x = 0: return math.sqrt(x) else: return None def bar(x): if x = 0: return math.sqrt(x) def bar(x): if x. With the acceptance of, the style rules for function annotations are changing. In order to be forward compatible, function annotations in Python 3 code should preferably use syntax.
(There are some formatting recommendations for annotations in the previous section.). The experimentation with annotation styles that was recommended previously in this PEP is no longer encouraged. However, outside the stdlib, experiments within the rules of are now encouraged. For example, marking up a large third party library or application with style type annotations, reviewing how easy it was to add those annotations, and observing whether their presence increases code understandability. The Python standard library should be conservative in adopting such annotations, but their use is allowed for new code and for big refactorings. For code that wants to make a different use of function annotations it is recommended to put a comment of the form: # type: ignore near the top of the file; this tells type checker to ignore all annotations. (More fine-grained ways of disabling complaints from type checkers can be found in.).
Like linters, type checkers are optional, separate tools. Python interpreters by default should not issue any messages due to type checking and should not alter their behavior based on annotations. Users who don't want to use type checkers are free to ignore them. However, it is expected that users of third party library packages may want to run type checkers over those packages. For this purpose recommends the use of stub files:.pyi files that are read by the type checker in preference of the corresponding.py files.
Stub files can be distributed with a library, or separately (with the library author's permission) through the typeshed repo. For code that needs to be backwards compatible, type annotations can be added in the form of comments. See the relevant section of. Introduced variable annotations.
The style recommendations for them are similar to those on function annotations described above:. Annotations for module level variables, class and instance variables, and local variables should have a single space after the colon. There should be no space before the colon. If an assignment has a right hand side, then the equality sign should have exactly one space on both sides. Yes: code: int class Point: coords: Tupleint, int label: str = '. No: code:int # No space after colon code: int # Space before colon class Test: result: int=0 # No spaces around equality sign.
Although the is accepted for Python 3.6, the variable annotation syntax is the preferred syntax for stub files on all versions of Python (see for details). Footnotes Hanging indentation is a type-setting style where all the lines in a paragraph are indented except the first line.
In the context of Python, the term is used to describe a style where the opening parenthesis of a parenthesized statement is the last non-whitespace character of the line, with subsequent lines being indented until the closing parenthesis.
1.7.0 (2016-01-12) Announcements:. Repository moved to PyCQA Organization on GitHub: Changes:. Reverted the fix in #368, “options passed on command line are only ones accepted” feature. This has many unintended consequences in pep8 and flake8 and needs to be reworked when I have more time. Added support for Python 3.5.
(Issue #420 & #459). Added support for multi-line configfile option parsing.
(Issue #429). Improved parameter parsing. (Issues #420 & #456) Bugs:.
Fixed BytesWarning on Python 3. (Issue #459). 1.6.0 (2015-02-06) News:. Ian Lee joined the project as a maintainer. Changes:. Report E731 for lambda assignment. (Issue #277).
Report E704 for one-liner def instead of E701. Do not report this error in the default configuration. (Issue #277). Replace codes E111, E112 and E113 with codes E114, E115 and E116 for bad indentation of comments. (Issue #274). Report E266 instead of E265 when the block comment starts with multiple #.
(Issue #270). Report E402 for import statements not at the top of the file.
(Issue #264). Do not enforce whitespaces around. operator. (Issue #292).
Strip whitespace from around paths during normalization. (Issue #339 / #343). Update -format documentation.
(Issue #198 / Pull Request #310). Add.tox/ to default excludes. (Issue #335). Do not report E121 or E126 in the default configuration. (Issues #256 / #316). Allow spaces around the equals sign in an annotated function.
(Issue #357). Allow trailing backslash if in an inline comment.
(Issue #374). If -config is used, only that configuration is processed.
Otherwise, merge the user and local configurations are merged. (Issue #368 / #369) Bug fixes:. Don’t crash if Checker.buildtokensline returns None. (Issue #306). Don’t crash if os.path.expanduser throws an ImportError. (Issue #297).
Missing space around keyword parameter equal not always reported, E251. (Issue #323).
Fix false positive E711/E712/E713. (Issues #330 and #336). Do not skip physical checks if the newline is escaped. (Issue #319). Flush sys.stdout to avoid race conditions with printing. See flake8 bug: for more details. (Issue #363).
1.5 (2014-03-26) Changes:. Report E129 instead of E125 for visually indented line with same indent as next logical line. (Issue #126). Report E265 for space before block comment. (Issue #190).
Report E713 and E714 when operators not in and is not are recommended. (Issue #236). Allow long lines in multiline strings and comments if they cannot be wrapped. (Issue #224). Optionally disable physical line checks inside multiline strings, using # noqa. (Issue #242).
Change text for E121 to report “continuation line under-indented for hanging indent” instead of indentation not being a multiple of 4. Report E131 instead of E121 / E126 if the hanging indent is not consistent within the same continuation block. It helps when error E121 or E126 is in the ignore list. Report E126 instead of E121 when the continuation line is hanging with extra indentation, even if indentation is not a multiple of 4. Bug fixes:. Allow the checkers to report errors on empty files. (Issue #240).
Fix ignoring too many checks when -select is used with codes declared in a flake8 extension. (Issue #216). Fix regression with multiple brackets. (Issue #214).
Fix StyleGuide to parse the local configuration if the keyword argument paths is specified. (Issue #246). Fix a false positive E124 for hanging indent. (Issue #254). Fix a false positive E126 with embedded colon. (Issue #144).
Fix a false positive E126 when indenting with tabs. (Issue #204). Fix behaviour when exclude is in the configuration file and the current directory is not the project directory. (Issue #247).
The logical checks can return None instead of an empty iterator. (Issue #250). Do not report multiple E101 if only the first indentation starts with a tab. (Issue #237). Fix a rare false positive W602. 1.4.6 (2013-07-02) Changes:.
Honor # noqa for errors E711 and E712. (Issue #180).
When both a tox.ini and a setup.cfg are present in the project directory, merge their contents. The tox.ini file takes precedence (same as before). (Issue #182). Give priority to -select over -ignore. (Issue #188). Compare full path when excluding a file. (Issue #186).
New option -hang-closing to switch to the alternative style of closing bracket indentation for hanging indent. Add error E133 for closing bracket which is missing indentation.
(Issue #103). Accept both styles of closing bracket indentation for hanging indent. Do not report error E123 in the default configuration.
(Issue #103) Bug fixes:. Do not crash when running AST checks and the document contains null bytes. (Issue #184). Correctly report other E12 errors when E123 is ignored. (Issue #103). Fix false positive E261/E262 when the file contains a BOM. (Issue #193).
Fix E701, E702 and E703 not detected sometimes. (Issue #196). Fix E122 not detected in some cases. (Issue #201 and #208). Fix false positive E121 with multiple brackets. (Issue #203). 1.4.5 (2013-03-06).
When no path is specified, do not try to read from stdin. The feature was added in 1.4.3, but it is not supported on Windows. Use - filename argument to read from stdin.
This usage is supported since 1.3.4. (Issue #170). Do not require setuptools in setup.py. It works around an issue with pip and Python 3. (Issue #172).
Add pycache to the ignore list. Change misleading message for E251. (Issue #171). Do not report false E302 when the source file has a coding cookie or a comment on the first line.
(Issue #174). Reorganize the tests and add tests for the API and for the command line usage and options. (Issues #161 and #162). Ignore all checks which are not explicitly selected when select is passed to the StyleGuide constructor. 1.4.2 (2013-02-10). Support AST checkers provided by third-party applications. Register new checkers with registercheck(funcorcls, codes).
Allow to construct a StyleGuide with a custom parser. Accept visual indentation without parenthesis after the if statement. (Issue #151).
Fix UnboundLocalError when using # noqa with continued lines. (Issue #158).
Re-order the lines for the StandardReport. Expand tabs when checking E12 continuation lines. (Issue #155). Refactor the testing class TestReport and the specific test functions into a separate test module.
1.4 (2012-12-22). Report E226 instead of E225 for optional whitespace around common operators (.,., /, + and -). This new error code is ignored in the default configuration because PEP 8 recommends to “use your own judgement”. (Issue #96). Lines with a # nopep8 at the end will not issue errors on line length E501 or continuation line indentation E12. (Issue #27).
Fix AssertionError when the source file contains an invalid line ending ' r r n'. (Issue #119). Read the pep8 section of tox.ini or setup.cfg if present.
(Issue #93 and #141). Add the Sphinx-based documentation, and publish it on. (Issue #105). 1.3.4 (2012-12-18). Fix false positive E124 and E128 with comments. (Issue #100). Fix error on stdin when running with bpython.
(Issue #101). Fix false positive E401. (Issue #104). Report E231 for nested dictionary in list. (Issue #142). Catch E271 at the beginning of the line.
(Issue #133). Fix false positive E126 for multi-line comments. (Issue #138). Fix false positive E221 when operator is preceded by a comma. (Issue #135).
Fix -diff failing on one-line hunk. (Issue #137). Fix the -exclude switch for directory paths. (Issue #111). Use - filename to read from standard input.
(Issue #128). Warning The internal API is backwards incompatible. Remove global configuration and refactor the library around a StyleGuide class; add the ability to configure various reporters. (Issue #35 and #66). Read user configuration from /.config/pep8 and local configuration from./.pep8.
(Issue #22). Fix E502 for backslash embedded in multi-line string. (Issue #68).
Fix E225 for Python 3 iterable unpacking (PEP 3132). (Issue #72). Enable the new checkers from the E12 series in the default configuration. Suggest less error-prone alternatives for E712 errors. Rewrite checkers to run faster (E22, E251, E27). Fixed a crash when parsed code is invalid (too many closing brackets).
Fix E127 and E128 for continuation line indentation. (Issue #74).
New option -format to customize the error format. (Issue #23). New option -diff to check only modified code. The unified diff is read from STDIN. Example: hg diff pep8 -diff (Issue #39). Correctly report the count of failures and set the exit code to 1 when the -doctest or the -testsuite fails. Correctly detect the encoding in Python 3.
(Issue #69). Drop support for Python 2.3, 2.4 and 3.0. 1.2 (2012-06-01). Add E121 through E128 for continuation line indentation.
These checks are disabled by default. If you want to force all checks, use switch -select=E,W. Patch by Sam Vilain. (Issue #64). Add E721 for direct type comparisons. (Issue #47).
Add E711 and E712 for comparisons to singletons. (Issue #46).
Fix spurious E225 and E701 for function annotations. (Issue #29). Add E502 for explicit line join between brackets. Fix E901 when printing source with -show-source.
Report all errors for each checker, instead of reporting only the first occurrence for each line. Option -show-pep8 implies -first. 0.7.0 (2012-03-26). Now -first prints only the first occurrence of each error. The -repeat flag becomes obsolete because it is the default behaviour. (Issue #6).
Allow to specify -max-line-length. (Issue #36). Make the shebang more flexible. (Issue #26).
Add testsuite to the bundle. (Issue #25). Fixes for Jython.
(Issue #49). Add PyPI classifiers. (Issue #43).
Fix the -exclude option. (Issue #48). Fix W602, accept raise with 3 arguments. (Issue #34). Correctly select all tests if DEFAULTIGNORE '. 0.6.0 (2010-09-19). Test suite reorganized and enhanced in order to check more failures with fewer test files.
Read the runtests docstring for details about the syntax. Fix E225: accept print sys.stderr, '.' . Fix E501 for lines containing multibyte encoded characters.
(Issue #7). Fix E221, E222, E223, E224 not detected in some cases. (Issue #16). Fix E211 to reject v = dic'a' 'b'. (Issue #17).
Exit code is always 1 if any error or warning is found. (Issue #10).ignore checks are now really ignored, especially in conjunction with -count. (Issue #8).
Blank lines with spaces yield W293 instead of W291: some developers want to ignore this warning and indent the blank lines to paste their code easily in the Python interpreter. Fix E301: do not require a blank line before an indented block.
(Issue #14). Fix E203 to accept NumPy slice notation a0,:. (Issue #13). Performance improvements. Fix decoding and checking non-UTF8 files in Python 3. Fix E225: reject True+False when running on Python 3.
Fix an exception when the line starts with an operator. Allow a new line before closing )or. 0.5.0 (2010-02-17). Changed the -count switch to print to sys.stderr and set exit code to 1 if any error or warning is found. E241 and E242 are removed from the standard checks. If you want to include these checks, use switch -select=E,W. (Issue #4).
Blank line is not mandatory before the first class method or nested function definition, even if there’s a docstring. (Issue #1).
Add the switch -version. Fix decoding errors with Python 3. (Issue #13 ).
Add -select option which is mirror of -ignore. Add checks E261 and E262 for spaces before inline comments. New check W604 warns about deprecated usage of backticks. New check W603 warns about the deprecated operator. Performance improvement, due to rewriting of E225. E225 now accepts:.
no whitespace after unary operator or similar. (Issue #9 ). lambda function with argument unpacking or keyword defaults.
Reserve “2 blank lines” for module-level logical blocks. (E303).
Allow multi-line comments. (E302, issue #10 ). 0.4 (2009-10-20). Support for all versions of Python from 2.3 to 3.1. New and greatly expanded self tests. Added -count option to print the total number of errors and warnings. Further improvements to the handling of comments and blank lines.
(Issue #1 and others changes.). Check all py files in directory when passed a directory (Issue #2 ). This also prevents an exception when traversing directories with non.py files. E231 should allow commas to be followed by ). (Issue #3 ). Spaces are no longer required around the equals sign for keyword arguments or default parameter values.
1 (, ) These issues refer to the.
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