{"id":17146,"date":"2022-10-23T07:00:01","date_gmt":"2022-10-23T01:30:01","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-explanation-of-c-implementation-pythons-len-function-closed\/"},"modified":"2022-10-23T07:00:01","modified_gmt":"2022-10-23T01:30:01","slug":"solved-explanation-of-c-implementation-pythons-len-function-closed","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-explanation-of-c-implementation-pythons-len-function-closed\/","title":{"rendered":"[Solved] explanation of C implementation python’s len function [closed]"},"content":{"rendered":"

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There is nothing special with this<\/em> function. Usually the functions written in C, especially those that do not call Python code, are much faster than ones written in Python.<\/p>\n

I am specifically taking the stance here that a reader knows<\/em> how C works, otherwise the explanation would rather be a book.<\/p>\n

The builtin_len<\/code> is the one that is called when len(foo)<\/code> is executed in Python code. The PyObject *obj<\/code> argument to the function references the object given as the argument (foo<\/code>), and PyObject *self<\/code> will contain a reference to the containing module of builtin_len<\/code>.<\/p>\n

Each container in Python must have a length between 0 and the maximum value allowed by Py_ssize_t<\/code>. PyObject_Size(obj);<\/code> is a function\/macro that gets the size of the given object through its obj->ob_type->tp_as_sequence->sq_length<\/code> or obj->ob_type->tp_as_mapping->mp_length<\/code>. Upon error an exception is set as raised for the current thread and a number < 0 (-1) is returned.<\/p>\n

The return NULL;<\/code> signifies the caller that an exception has occurred and it must act accordingly – if it is a function call instruction in Python bytecode, it will cause an exception to be raised; if it is C code, then it will behave in a manner similar to this function – returning NULL or invalid value if an exception occurred; or it can clear the exception or replace it with another one.<\/p>\n

Otherwise if greater than or equal to 0<\/strong>, the Py_ssize_t res<\/code> which is of a C integer type, is converted to a Python int<\/code><\/em> object, by either returning an existing int<\/code> object or constructing a new one. The Python int<\/code> object is called PyLong<\/code> in CPython 3 for historical reasons. PyLong_FromSsize_t()<\/code> is one of many functions – this one is able to convert any value of type Py_ssize_t<\/code> to a Python int<\/code> with the same value. The reference to this object, like all other objects, are kept as pointers to the (semi-opaque) PyObject<\/code> structure, and this is returned.<\/p>\n

The assert(PyErr_Occurred());<\/code> is an assertion that is in effect in debug builds of Python only. It asserts that upon getting a negative number from PyObject_Size<\/code>, signifying an exception being thrown, the exception has also been properly set; if not present, it will abort the entire CPython process outright. It isn’t in effect in release builds of Python because “asserts never fail”.<\/p>\n<\/p><\/div>\n

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2<\/span> <\/p><\/div>\n<\/div>\n

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solved explanation of C implementation python’s len function [closed] <\/p>\n","protected":false},"excerpt":{"rendered":"

[ad_1] There is nothing special with this function. Usually the functions written in C, especially those that do not call Python code, are much faster than ones written in Python. I am specifically taking the stance here that a reader knows how C works, otherwise the explanation would rather be a book. The builtin_len is … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[324,4282,349,1405],"class_list":["post-17146","post","type-post","status-publish","format-standard","hentry","category-solved","tag-c","tag-cpython","tag-python","tag-python-internals"],"yoast_head":"\n[Solved] explanation of C implementation python's len function [closed] - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-explanation-of-c-implementation-pythons-len-function-closed\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] explanation of C implementation python's len function [closed] - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] There is nothing special with this function. 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