從上學時開始，通常是用C來求階乘，今天無事，用python寫了一下，主要在于學習lambda和reduce這兩個函數的使用。 實現： ~~~ #!/usr/bin/env python #-*- coding: utf-8 -*- import time def test_factorial_reduce(): ''' Function:使用reduce函數 Input：NONE Output: NONE author: socrates blog:http://blog.csdn.net/dyx1024 date:2012-02-19 ''' time_begin = time.clock() print reduce(lambda x,y:x*y, range(1, long(raw_input("please input a number ( > 0):")))) print "Use time: %s" % (time.clock() - time_begin) return; def test_factorial_math(): ''' Function:使用math庫函數 Input：NONE Output: NONE author: socrates blog:http://blog.csdn.net/dyx1024 date:2012-02-19 ''' import math time_begin = time.clock() print math.factorial(long(raw_input("please input a number ( > 0):"))) print "Use time: %s" % (time.clock() - time_begin) if __name__ == '__main__': print '*' * 50 + "Use reduce" + '*' * 50 test_factorial_reduce() print '*' * 50 + "Use math api" + '*' * 50 test_factorial_math() ~~~ 測試： ~~~ **************************Use reduce************************** please input a number ( > 0):50 608281864034267560872252163321295376887552831379210240000000000 Use time: 3.3163365735 **************************Use math api************************** please input a number ( > 0):50 30414093201713378043612608166064768844377641568960512000000000000 Use time: 3.70409004496 ~~~ 我們感興趣的不在程序本身，我想更多地會關注lambda和reduce這兩個函數，我們來看一下： lambda 手冊中這樣描述： ~~~ lambda An anonymous inline function consisting of a single expression which is evaluated when the function is called. The syntax to create a lambda function is lambda [arguments]: expression ~~~ 其實lambda就是個匿名函數，它本身是一個表達式，而def為一個語句，這就是說lambda可以用于函數中做為參數等，但def這個語句不能。 我們的?lambda x,y:x*y 語句等價于下面這個函數： ~~~ def my_func(x, y): return x * y ~~~ ?reduce ?手冊中這樣描述： ~~~ reduce(function, iterable[, initializer]) Apply function of two arguments cumulatively to the items of iterable, from left to right, so as to reduce the iterable to a single value. For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates ((((1+2)+3)+4)+5). The left argument, x, is the accumulated value and the right argument, y, is the update value from the iterable. If the optional initializer is present, it is placed before the items of the iterable in the calculation, and serves as a default when the iterable is empty. If initializer is not given and iterable contains only one item, the first item is returned. ~~~ 就是用函數function對序列，如list中的元素進行處理，每次處理兩個數據項(一個是前次處理的結果，一個是序列中的下一個元素)，如此反復的遞歸處理，最后對整個序列求出一個單一的返回值。 改寫一下上面的程序，很快可以理解這句話的意思： ~~~ def my_func(x, y): print 'x = %d, y = %d' %(x, y) return x * y print reduce(my_func, range(1, long(raw_input("please input a number ( > 0):")))) ~~~ 運行結果： ~~~ please input a number ( > 0):50 x = 1, y = 2 x = 2, y = 3 x = 6, y = 4 x = 24, y = 5 x = 120, y = 6 x = 720, y = 7 x = 5040, y = 8 x = 40320, y = 9 x = 362880, y = 10 x = 3628800, y = 11 x = 39916800, y = 12 x = 479001600, y = 13 x = 6227020800, y = 14 x = 87178291200, y = 15 x = 1307674368000, y = 16 x = 20922789888000, y = 17 x = 355687428096000, y = 18 x = 6402373705728000, y = 19 x = 121645100408832000, y = 20 x = 2432902008176640000, y = 21 x = 51090942171709440000, y = 22 x = 1124000727777607680000, y = 23 x = 25852016738884976640000, y = 24 x = 620448401733239439360000, y = 25 x = 15511210043330985984000000, y = 26 x = 403291461126605635584000000, y = 27 x = 10888869450418352160768000000, y = 28 x = 304888344611713860501504000000, y = 29 x = 8841761993739701954543616000000, y = 30 x = 265252859812191058636308480000000, y = 31 x = 8222838654177922817725562880000000, y = 32 x = 263130836933693530167218012160000000, y = 33 x = 8683317618811886495518194401280000000, y = 34 x = 295232799039604140847618609643520000000, y = 35 x = 10333147966386144929666651337523200000000, y = 36 x = 371993326789901217467999448150835200000000, y = 37 x = 13763753091226345046315979581580902400000000, y = 38 x = 523022617466601111760007224100074291200000000, y = 39 x = 20397882081197443358640281739902897356800000000, y = 40 x = 815915283247897734345611269596115894272000000000, y = 41 x = 33452526613163807108170062053440751665152000000000, y = 42 x = 1405006117752879898543142606244511569936384000000000, y = 43 x = 60415263063373835637355132068513997507264512000000000, y = 44 x = 2658271574788448768043625811014615890319638528000000000, y = 45 x = 119622220865480194561963161495657715064383733760000000000, y = 46 x = 5502622159812088949850305428800254892961651752960000000000, y = 47 x = 258623241511168180642964355153611979969197632389120000000000, y = 48 x = 12413915592536072670862289047373375038521486354677760000000000, y = 49 608281864034267560872252163321295376887552831379210240000000000 ~~~