Macro definition in python 37/29/2023 The problem is solved for the current program, but this solution is not robust. Until a variable named INCIa is created, this solution produces the correct output: In C, this problem can be illustrated by the following fragment: In programming languages that have non-hygienic macro systems, it is possible for existing variable bindings to be hidden from a macro by variable bindings that are created during its expansion. The term "hygiene" was coined in Kohlbecker et al.'s 1986 paper that introduced hygienic macro expansion, inspired by terminology used in mathematics. Hygienic macros are a programmatic solution to the capture problem that is integrated into the macro expander. Macro writers would use language features that would generate unique identifiers (e.g., gensym) or use obfuscated identifiers to avoid the problem. The general problem of accidental capture was well known in the Lisp community before the introduction of hygienic macros. They are a feature of programming languages such as Scheme, Dylan, Rust, Nim, and Julia. In computer science, hygienic macros are macros whose expansion is guaranteed not to cause the accidental capture of identifiers. ( November 2016) ( Learn how and when to remove this template message) Please help improve it to make it understandable to non-experts, without removing the technical details. Performance-critical objects (such as numbers).This article may be too technical for most readers to understand. To participate in the weak reference mechanism without incurring the overhead on One of the goals of Python's weak reference implementation is to allow any type Occurs, tp_iternext should always set an exceptionĪnd return NULL. The exception can yield slightly better performance. StopIteration in addition to returning NULL avoiding May return NULL without setting an exception, or it may set If the iteration has reached the end, tp_iternext Return a new reference to the next object in the iteration, if there is one. Tp_iter handler should return a new reference Iteration, such as file objects) can implement tp_iterīy returning a new reference to themselves - and should also thereforeĪny iterator object should implement both tp_iter Objects which can only be iterated over once (usually due to side effects of Independent iterators, a new iterator should be created and returned by Here the same guidelinesįor collections (such as lists and tuples) which can support multiple Handler, which must return an iterator object. To the Python _iter_() method, while tp_iternextĬorresponds to the Python _next_() method.Īny iterable object must implement the tp_iter In the case of an error, they should set anĮxception and return NULL. Take exactly one parameter, the instance for which they are being called,Īnd return a new reference. These functions provide support for the iterator protocol. * Iterators */ getiterfunc tp_iter iternextfunc tp_iternext To indicate the presence of a slot, but a slot may still be unfilled.) (The flagīit does not indicate that the slot values are non- NULL. That the slots are present and should be checked by the interpreter. For newer protocols there areĪdditional slots in the main type object, with a flag bit being set to indicate For protocols which depend on several handler routinesįrom the type implementation, the older protocols have been defined as optionalīlocks of handlers referenced by the type object. Other protocols haveīeen added over time. Protocols have been part of Python since the beginning. In particular, the number, mapping, and sequence
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