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...Definition Constants Functions Example Implementation References Copyright Rejection Notice This PEP has been rejected. After sitting open for four years, it has failed to generate sufficient community interest. Several ideas of this PEP were implemented for Python 2.6. float('inf') and repr(float('inf')) are now guaranteed to work on every supported platform with IEEE 754 semantics. However the eval(repr(float('inf'))) roundtrip is still not supported unless you define inf and nan yourself...
...constants" we force programmers to give up good habits. Named constants are introduced in most languages to solve the problem of "magic numbers" occurring in the source code. For example, sys.maxint is a lot more readable than 2147483647. Raymond proposes to use string literals instead of named "enums", observing that the string literal's content can be the name that the constant would otherwise have. Thus, we could write "case 'IGNORECASE':" instead of "case re.IGNORECASE:". However, if the...
...definition and such an absence should be treated specially. Difficult to implement Eric Traut from the Pyright type checker team has stated that implementing a Union[..., Missing]-style notation would be difficult. [2] Introduces a second null-like value into Python Defining a new Missing type-level constant would be very close to introducing a new Missing value-level constant at runtime, creating a second null-like runtime value in addition to None. Having two different null-like constants ...
...constants, and internal constants. User-code facing constants like os.SEEK_*, socket module constants, decimal rounding modes and HTML error codes could require backwards compatibility since user code may expect integers. IntEnum as described above provides the required semantics; being a subclass of int, it does not affect user code that expects integers, while on the other hand allowing printable representations for enumeration values: >>> import socket >>> family = socket....
...definition to provide additional metadata about each field in the class. This metadata can describe, for example, default values, or indicate whether the field should be included in the synthesized __init__ method. Field descriptors can be omitted in cases where additional metadata is not required: @dataclass class Employee: # Field with no descriptor name: str # Field that uses field descriptor class instance age: Optional[int] = field(default=None, init=False) # Field wi...
...definition, a function definition or as first string literal in a module. The string literals are added to the objects in question under the __doc__ attribute and are from then on available for introspection tools which can extract the contained information for help, debugging and documentation purposes. Docstrings appearing in locations other than the ones mentioned are simply ignored and don't result in any code generation. Here is an example: class C: "class C doc-string" a = 1 ...
...constant_pattern) ':' or_pattern | '**' capture_pattern Mapping pattern is a generalization of iterable unpacking to mappings. Its syntax is similar to dictionary display but each key and value are patterns "{" (pattern ":" pattern)+ "}". A **rest pattern is also allowed, to extract the remaining items. Only literal and constant value patterns are allowed in key positions: import constants match config: case {"route": route}: process_route(route) case {constants.DEFAULT_P...
...Constant(), and PyModule_AddStringConstant(). Cleaned up definition of NULL in C source code; all definitions were removed and add #error to Python.h if NULL isn't defined after #include of stdio.h. Py_PROTO() macros that were removed in 2.0b1 have been restored for backwards compatibility (at the source level) with old extensions. A wrapper API was added for signal() and sigaction(). Instead of either function, always use PyOS_getsig() to get a signal handler and PyO...
...constants. A proposed rule to use a leading dot (e.g. .CONSTANT) for that purpose was criticised because it was felt that the dot would not be a visible-enough marker for that purpose. Partly inspired by forms found in other programming languages, a number of different markers/sigils were proposed (such as ^CONSTANT, $CONSTANT, ==CONSTANT, CONSTANT?, or the word enclosed in backticks), although there was no obvious or natural choice. The current proposal therefore leaves the discussion and pos...
...definition. Other classes don't have a natural ordering of their attributes so you're required to use explicit names in your pattern to match with their attributes. However, it's possible to manually specify the ordering of the attributes allowing positional matching, like in this alternative definition: class Click: __match_args__ = ("position", "button") def __init__(self, pos, btn): self.position = pos self.button = btn ... The __match_args__ special attribut...
...definition file for python3.dll [1]. Global Variables Global variables representing types and exceptions are available to applications. In addition, selected global variables referenced in macros (such as Py_True and Py_False) are available. A complete list of global variable definitions is given in the python3.def file [1]; those declared DATA denote variables. Other Macros All macros defining symbolic constants are available to applications; the numeric values will not change. In addition,...
...Definition Language (ASDL) [Wang97]. The definition of the AST nodes for Python is found in the file Parser/Python.asdl . Each AST node (representing statements, expressions, and several specialized types, like list comprehensions and exception handlers) is defined by the ASDL. Most definitions in the AST correspond to a particular source construct, such as an 'if' statement or an attribute lookup. The definition is independent of its realization in any particular programming language. The fol...
...definitions, but just one big technical change: the Stable ABI will be explicitly listed in a human-maintained “manifest” file. There have been efforts to collect such lists automatically, e.g. by scanning the symbols exported from Python. Such automation might seem easier to maintain than a handcrafted file, but has major issues: for example, the set exported symbols has platform-specific variations. Also, the cost of updating an explicit manifest is small compared to the overall work that shou...
...constants See also optimizations implemented in fatoptimizer, a static optimizer for Python 3.6. The following issues can be implemented with an AST optimizer: Issue #1346238: A constant folding optimization pass for the AST Issue #2181: optimize out local variables at end of function Issue #2499: Fold unary + and not on constants Issue #4264: Patch: optimize code to use LIST_APPEND instead of calling list.append Issue #7682: Optimisation of if with constant expression Issue #10399: AST Optimi...
...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...
...definitions, by maintaining a reference to the class-level scope. This idea, too, was quickly rejected. PEP 563 summarizes the above discussion What's puzzling is PEP 563's own changes to the scoping rules of annotations—it also doesn't permit annotations to reference class-level definitions. It's not immediately clear why an inability to reference class-level definitions was enough to reject using "implicit lambda expressions" for annotations, but was acceptable for stringized annotations. In...
...Constant AST node prepopulated with a complex number. If that was the way things worked, then complex literals could be accepted through a similar mechanism to any other literal. This isn't how complex literals are handled, however. Instead, they're passed through to the AST as regular BinOp nodes, and then the constant folding pass on the AST resolves them down to Constant nodes with a complex value. For the parser to resolve complex literals directly, the compiler would need to be able to tell...
...definition time. Instead, they are preserved in __annotations__ in string form. This change is being introduced gradually, starting with a __future__ import in Python 3.7. Rationale and Goals PEP 3107 added support for arbitrary annotations on parts of a function definition. Just like default values, annotations are evaluated at function definition time. This creates a number of issues for the type hinting use case: forward references: when a type hint contains names that have not been defi...
...Definition, as established by the Open Source Initiative (see http://www.opensource.org/). Add the following paragraph to the end of the mission statement (after "Encourages and facilitates Python-related research in the public interest."): "Open source" is defined as: freely available technology licensed under terms compatible with Version 1.9 (or later) of the Open Source Definition, as established by the Open Source Initiative (see http://www.opensource.org/). Appro...
...definition macros Backwards Compatibility Performance Implications Implementation Reference Implementation Copyright Abstract This PEP adds support for syntactic macros to Python. A macro is a compile-time function that transforms a part of the program to allow functionality that cannot be expressed cleanly in normal library code. The term "syntactic" means that this sort of macro operates on the program's syntax tree. This reduces the chance of mistranslation that can happen with text-...