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...constructor the same three arguments that are passed to the default class constructor or to an extension's metaclass: name, bases, and namespace. It is easy to be confused by what exactly happens when using a metaclass, because we lose the absolute distinction between classes and instances: a class is an instance of a metaclass (a ``metainstance''), but technically (i.e. in the eyes of the python runtime system), the metaclass is just a class, and the metainstance is just an instance. ...
...Constructors There are four forms of constructors, applicable to both bytes and bytearray: bytes(<bytes>), bytes(<bytearray>), bytearray(<bytes>), bytearray(<bytearray>): simple copying constructors, with the note that bytes(<bytes>) might return its (immutable) argument, but bytearray(<bytearray>) always makes a copy. bytes(<str>, <encoding>[, <errors>]), bytearray(<str>, <encoding>[, <errors>]): encode a text string. Not...
...constructor? And if so, does that alternate constructor need to have the same name as the original constructor? Customizing the dict in which the block is executed Should users of the make-statement be able to determine in which dict object the code is executed? This would allow the make-statement to be used in situations where a normal dict object would not suffice, e.g. if order and repeated names must be allowed. Allowing this sort of customization could allow XML to be written without r...
...Constructors for a definition 'raw-unicode-escape': See Unicode Constructors for a definition 'native': Dump of the Internal Format used by Python Common aliases should also be provided per default, e.g. 'latin-1' for 'iso-8859-1'. Note: 'utf-16' should be implemented by using and requiring byte order marks (BOM) for file input/output. All other encodings such as the CJK ones to support Asian scripts should be implemented in separate packages which do not get included in the core Py...
...definition of the save method would mean that a D instance, when requested to save itself, only saves the A and B parts of its data, but not the part of its data defined by class C! C++ notices that D inherits two conflicting definitions of method m, and issues an error message. The author of D is then supposed to override m to resolve the conflict. But what is D's definition of m supposed to do? It can call B's m followed by C's m, but because both definitions call the definition of...
...constructor, rather than passing value as a single argument (and an empty tuple calls the constructor without arguments). This makes a difference because there's a difference between f(a, b) and f((a, b)). These are all compromises - they work well with the kind of arguments that the standard exceptions typically take (like a simple string). For clarity in new code, the form raise class(argument, ...) is recommended (i.e. make an explicit call to the constructor). H...
...constructor, it is similar to semantics of functions, but a function takes a value and returns a value, while generic type constructor takes a type and "returns" a type. It is common when a particular class or a function behaves in such a type generic manner. Consider two examples: Container classes, such as list or dict, typically contain only values of a particular type. Therefore, a user might want to type annotate them as such: users = [] # type: List[UserID] users.append(UserID(42)) # OK ...
...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...
...constructor of the bytes object has the following signature: bytes([initializer[, encoding]]) If no arguments are provided then a bytes object containing zero elements is created and returned. The initializer argument can be a string (in 2.6, either str or unicode), an iterable of integers, or a single integer. The pseudo-code for the constructor (optimized for clear semantics, not for speed) is: def bytes(initializer=0, encoding=None): if isinstance(initializer, int): # In 2.6, int -&g...
...Constructors Access to the database is made available through connection objects. The module must provide the following constructor for these: connect( parameters... ) Constructor for creating a connection to the database. Returns a Connection Object. It takes a number of parameters which are database dependent. [1] Globals These module globals must be defined: apilevel String constant stating the supported DB API level. Currently only the strings "1.0" and "2.0" are allowed. If not given,...
...definition syntax with typing.TypedDict as the sole base class: from typing import TypedDict class Movie(TypedDict): name: str year: int Movie is a TypedDict type with two items: 'name' (with type str) and 'year' (with type int). A type checker should validate that the body of a class-based TypedDict definition conforms to the following rules: The class body should only contain lines with item definitions of the form key: value_type, optionally preceded by a docstring. The syntax fo...
...definition. Such a docstring becomes the __doc__ special attribute of that object. All modules should normally have docstrings, and all functions and classes exported by a module should also have docstrings. Public methods (including the __init__ constructor) should also have docstrings. A package may be documented in the module docstring of the __init__.py file in the package directory. String literals occurring elsewhere in Python code may also act as documentation. They are not recognized...
...constructor with the number of bytes to allocate. For example: b = bytes(100000) # alloc 100K bytes The constructor can also take another bytes object. This will be useful for the implementation of unpickling, and in converting a read-write bytes object into a read-only one. An optional second argument will be used to designate creation of a readonly bytes object. From the C API, the bytes object can be allocated using any of the following signatures: PyObject* PyBytes_FromLength(LONG_LON...
...definition file. Like YACC, YAPPS supports custom code before and after the grammar definition. YAPPS parsers integrate with the scanner through a Scanner object, which is passed to the parser as a constructor argument. Even though YAPPS supports definition of tokens in the grammar, we have not used this capability in XPath, since we have provided my own scanner class. The YAPPS parser will only require a token() method from the scanner object, which must return a four-tuple (start, e...
...constructors. In essence, the certificate object in this module could be as abstract as a handle that can be used to locate a specific certificate. Concrete implementations may choose to provide alternative constructors, e.g. to load certificates from HSMs. If a common interface emerges for doing this, this module may be updated to provide a standard constructor for this use-case as well. Concrete implementations should aim to have Certificate objects be hashable if at all possible. This will he...
...definition syntax, you are free to use inheritance, metaclasses, docstrings, user-defined methods, class factories, and other Python class features. A class decorator is provided which inspects a class definition for variables with type annotations as defined in PEP 526, "Syntax for Variable Annotations". In this document, such variables are called fields. Using these fields, the decorator adds generated method definitions to the class to support instance initialization, a repr, comparison met...
...constructor: The results of this constructor can be somewhat unpredictable and its use is generally not recommended. From tuples Aahz suggested to construct from tuples: it's easier to implement eval()'s round trip and "someone who has numeric values representing a Decimal does not need to convert them to a string." The structure will be a tuple of three elements: sign, number and exponent. The sign is 1 or 0, the number is a tuple of decimal digits and the exponent is a signed int or lon...