built-in

问题 I know that some functions like sin cos min max memcpy may be treated not as normal functions but may be replaced by built-in functions (which may be more optimal than merely inline function calls, when the replacement is (an) actual processor instruction(s), such as directly calling the FSIN instruction for standard sin function when compiled for an x86 with a floating point unit). The question I would like to use power of built-in functions (in C/C++ mostly in mingw/gcc maybe other compiler

问题 I know that some functions like sin cos min max memcpy may be treated not as normal functions but may be replaced by built-in functions (which may be more optimal than merely inline function calls, when the replacement is (an) actual processor instruction(s), such as directly calling the FSIN instruction for standard sin function when compiled for an x86 with a floating point unit). The question I would like to use power of built-in functions (in C/C++ mostly in mingw/gcc maybe other compiler

问题 I write a algorithm (taken from "The C Programming Language") that counts the number of 1-bits very fast: int countBit1Fast(int n) { int c = 0; for (; n; ++c) n &= n - 1; return c; } But a friend told me that __builtin__popcount(int) is a lot faster, but less portable. I give it a try and was MANY times faster! Why it's so fast? I want to count bits as fast as possible, but without stick to a particular compiler. EDIT: I may use it on PIC micro-controllers and maybe on non-intel processors,

问题 I am currently using python 3.6, and I was playing around with the id() function. When I run the following code in IDLE, x = 1 print(id(x), id(1)) The two memory addresses are the same. (1499456272 for me) My understanding is the integer 1, which is an object, has a memory address, and when the object is assigned to x, the variable gains the same memory address of the object. (not sure if this is correct) When I replicate the above code using a string, for instance s = "a" print(id(s), id("a"

问题 How do I return a list of the 3 lowest values in another list. For example I want to get the 3 lowest values of this list: in_list = [1, 2, 3, 4, 5, 6] input: function(in_list, 3) output: [1, 2, 3] 回答1: You can use heapq.nsmallest: >>> from heapq import nsmallest >>> in_list = [1, 2, 3, 4, 5, 6] >>> nsmallest(3, in_list) [1, 2, 3] >>> 回答2: If you could sort,you can get frst 3 elements as below: alist=[6, 4, 3, 2, 5, 1] sorted(alist)[:3] Output: [1,2,3] 回答3: even simpler without modules

问题 How do I return a list of the 3 lowest values in another list. For example I want to get the 3 lowest values of this list: in_list = [1, 2, 3, 4, 5, 6] input: function(in_list, 3) output: [1, 2, 3] 回答1: You can use heapq.nsmallest: >>> from heapq import nsmallest >>> in_list = [1, 2, 3, 4, 5, 6] >>> nsmallest(3, in_list) [1, 2, 3] >>> 回答2: If you could sort,you can get frst 3 elements as below: alist=[6, 4, 3, 2, 5, 1] sorted(alist)[:3] Output: [1,2,3] 回答3: even simpler without modules

问题 How do I return a list of the 3 lowest values in another list. For example I want to get the 3 lowest values of this list: in_list = [1, 2, 3, 4, 5, 6] input: function(in_list, 3) output: [1, 2, 3] 回答1: You can use heapq.nsmallest: >>> from heapq import nsmallest >>> in_list = [1, 2, 3, 4, 5, 6] >>> nsmallest(3, in_list) [1, 2, 3] >>> 回答2: If you could sort,you can get frst 3 elements as below: alist=[6, 4, 3, 2, 5, 1] sorted(alist)[:3] Output: [1,2,3] 回答3: even simpler without modules

问题 At what point do methods in Python acquire a get property? —As soon as they're defined in the class? Why does Python let me define a method without any arguments (not even a first self argument)? I know how to use classmethod and staticmethod , and I know that they're built-in functions, but what happens to a function that is so-decorated? Essentially, I'm wondering about the "magic" that happens between class definition and class construction. 回答1: Check this out. http://docs.python.org

问题 At what point do methods in Python acquire a get property? —As soon as they're defined in the class? Why does Python let me define a method without any arguments (not even a first self argument)? I know how to use classmethod and staticmethod , and I know that they're built-in functions, but what happens to a function that is so-decorated? Essentially, I'm wondering about the "magic" that happens between class definition and class construction. 回答1: Check this out. http://docs.python.org

问题 Today, I automatically wrote some thing like this: class Foo(): def __init__(self, x): self.x = x s = [Foo(1), Foo(2), Foo(3)] sum_x = sum(s, key = lambda foo: foo.x) And got this: TypeError: sum() takes no keyword arguments Is there any special reason for sum() does not have a key arg? 回答1: Because you can just write sum(foo.x for foo in s) instead. If you tried to do this with one of the functions that does take a key argument ( sorted , min , max , etc.), the function would end up