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...declarations PEP:3117 Title:Postfix type declarations Author:Georg Brandl <georg at python.org> Status:Rejected Type:Standards Track Created:01-Apr-2007 Python-Version:3.0 Post-History: Contents Abstract Rationale Specification Unicode replacement units The typedef statement Example Compatibility issues Rejection References Acknowledgements Copyright Abstract This PEP proposes the addition of a postfix type declaration syntax to Python. It also specifies a new typedef...
...objects store their members in a dictionary, in which ordering is unimportant, and members are accessed strictly by name. However, Python is often used to interface with external systems in which the members are organized according to an implicit ordering. Examples include declaration of C structs; COM objects; Automatic translation of Python classes into IDL or database schemas, such as used in an ORM; and so on. In such cases, it would be useful for a Python programmer to specify such ordering...
...object is returned; a reference to an existing object is fine too. The return value should always be a new reference, owned by the caller. Once the tp_new slot has returned an object, further initialization is attempted by calling the tp_init() slot of the resulting object's type, if not NULL. This has the following signature: int tp_init(PyObject *self, PyObject *args, PyObject *kwds) It corresponds more closely to the __init__() method of classic classes, and in fac...
...object,), {'x':1, 'foo':<function foo at ...>}) The class statement is just syntactic sugar for the above assignment statement, but clearly a very useful sort of syntactic sugar. It avoids not only the repetition of C, but also simplifies the creation of the dict by allowing it to be expressed as a series of statements. Historically, type instances (a.k.a. class objects) have been the only objects blessed with this sort of syntactic support. The make statement aims to extend this suppor...
...declaration [2] in the source file. The Unicode-specific escape sequences \uxxxx, \Uxxxxxxxx, and \N{name} are unrecognized in Python 2.x and forbidden in Python 3000. Adjacent bytes literals are subject to the same concatenation rules as adjacent string literals [3]. A bytes literal adjacent to a string literal is an error. Semantics Each evaluation of a bytes literal produces a new bytes object. The bytes in the new object are the bytes represented by the shortstringitem or longstringitem ...
...declaration. Indented lines below the function declaration declare parameters, one per line; lines below those that are indented even further are per-parameter docstrings. Finally, the first line dedented back to column 0 end parameter declarations and start the function docstring. Parameter docstrings are optional; function docstrings are not. Functions that specify no arguments may simply specify the function declaration followed by the docstring. Module and Class Declarations When a C fil...
...objects a and b to find out their type, which is not known at compile time. It then invokes the appropriate addition operation, which may be an overloaded user-defined method. Java, on the other hand, can perform an efficient integer or floating point addition, but requires variable declarations for a and b, and does not allow overloading of the + operator for instances of user-defined classes. For these reasons, Python is much better suited as a "glue" language, while Java is better ch...
...objects. Names are introduced by name binding operations. Each occurrence of a name in the program text refers to the binding of that name established in the innermost function block containing the use. The name binding operations are argument declaration, assignment, class and function definition, import statements, for statements, and except clauses. Each name binding occurs within a block defined by a class or function definition or at the module level (the top-level code block). If a name...
...Declaration The proposals in this category all suggest a new kind of declaration statement similar to JavaScript's var. A few possible keywords have been proposed for this purpose: scope x [4] var x [4] [9] my x [13] In all these proposals, a declaration such as var x in a particular scope S would cause all references to x in scopes nested within S to refer to the x bound in S. The primary objection to this category of proposals is that the meaning of a function definition would become contex...
...declaration. A solution to this problem is to move the transformation of the method closer to the method's own declaration. The intent of the new syntax is to replace def foo(cls): pass foo = synchronized(lock)(foo) foo = classmethod(foo) with an alternative that places the decoration in the function's declaration: @classmethod @synchronized(lock) def foo(cls): pass Modifying classes in this fashion is also possible, though the benefits are not as immediately apparent. Almost certa...
...objects: regular objects (like lists, ints, functions) and meta-objects. Types and classes are meta-objects. Meta-objects are also regular objects, but we're mostly interested in them because they are referenced by the __class__ attribute of regular objects (or by the __bases__ attribute of other meta-objects). The class introspection API consists of the following elements: the __class__ and __dict__ attributes on regular objects; the __bases__ and __dict__ attributes on meta-objects; preceden...
...object stored in the attribute is not a descriptor. Since functions are descriptors, we must take care to not honor the descriptor protocol for all objects. Otherwise, all module-level functions will suddenly become bound to the module instance as if they were method calls on the module object. The module handle would be passed in as a "self" argument to all module-level functions. Both challenges can be solved with the same approach: we define a new "fast subclass" flag that means "This obje...
...object -- it is not consistent with most types (e.g. you can't use an object() instance where an int is expected). IOW both Any and object mean "any type is allowed" when used to annotate an argument, but only Any can be passed no matter what type is expected (in essence, Any declares a fallback to dynamic typing and shuts up complaints from the static checker). Here's an example showing how these rules work out in practice: Say we have an Employee class, and a subclass Manager: class Employee:...
...Object PyTypeObject Type Objects The structure of type objects is not available to applications; declaration of "static" type objects is not possible anymore (for applications using this ABI). Instead, type objects get created dynamically. To allow an easy creation of types (in particular, to be able to fill out function pointers easily), the following structures and functions are available: typedef struct{ int slot; /* slot id, see below */ void *pfunc; /* function pointer */ } PyTyp...
...objects from the given Unicode data and creating string objects from the Unicode literal data by first reencoding the UTF-8 data into 8-bit string data using the given file encoding Note that Python identifiers are restricted to the ASCII subset of the encoding, and thus need no further conversion after step 4. Implementation For backwards-compatibility with existing code which currently uses non-ASCII in string literals without declaring an encoding, the implementation will be introduced i...
...object type called an attribute access handler. Objects of this type have the following attributes: name (e.g. XXX, not __attr__XXX__) method (pointer to a method object) In PyClass_New, methods of the appropriate form will be detected and converted into objects (just like unbound method objects). These are stored in the class __dict__ under the name XXX. The original method is stored as an unbound method under its original name. If there are any attribute access handlers in an instance at all...
...object. The subclass __new__ can do two things to affect the resulting object: pass different arguments to the base class __new__, and modify the resulting object after it's been created (for example to initialize essential instance variables). __new__ must return an object. There's nothing that requires that it return a new object that is an instance of its class argument, although that is the convention. If you return an existing object, the constructor call will still call its __i...
...object Either native coroutine object or generator-based coroutine object. Future-like object An object with an __await__ method, or a C object with tp_as_async->am_await function, returning an iterator. Can be consumed by an await expression in a coroutine. A coroutine waiting for a Future-like object is suspended until the Future-like object's __await__ completes, and returns the result. See Await Expression for details. Awaitable A Future-like object or a coroutine object. See Await Exp...
...object, but alternative return values could be specified in list form. C-declarations This optional section contains C variable declarations. Since the converter functions have been declared beforehand, the preprocessor can type-check the declarations. Cleanup The optional cleanup section contains literal C code that will be inserted unmodified after the implementation function. Output The output section contains the code emitted by the preprocessor. Positional-only arguments Functions ...
...object, **kwargs: object) -> R: await log_to_database() return f(*args, **kwargs) return inner @add_logging def takes_int_str(x: int, y: str) -> int: return x + 7 await takes_int_str(1, "A") await takes_int_str("B", 2) # fails at runtime add_logging, a decorator which logs before each entry into the decorated function, is an instance of the Python idiom of one function passing all arguments given to it over to another function. This is done through the combination of the *a...