{"id":564,"date":"2017-07-09T16:37:07","date_gmt":"2017-07-09T08:37:07","guid":{"rendered":"https:\/\/9dream.me\/?p=564"},"modified":"2017-07-09T16:37:07","modified_gmt":"2017-07-09T08:37:07","slug":"python%e5%9f%ba%e7%a1%807-7-itertools","status":"publish","type":"post","link":"https:\/\/9dream.me\/python%e5%9f%ba%e7%a1%807-7-itertools\/","title":{"rendered":"Python\u57fa\u78407.7-itertools"},"content":{"rendered":"

Python\u7684\u5185\u5efa\u6a21\u5757itertools<\/code>\u63d0\u4f9b\u4e86\u975e\u5e38\u6709\u7528\u7684\u7528\u4e8e\u64cd\u4f5c\u8fed\u4ee3\u5bf9\u8c61\u7684\u51fd\u6570\u3002<\/p>\n

\u9996\u5148\uff0c\u6211\u4eec\u770b\u770bitertools<\/code>\u63d0\u4f9b\u7684\u51e0\u4e2a\u201c\u65e0\u9650\u201d\u8fed\u4ee3\u5668\uff1a<\/p>\n

>>> <\/span>import<\/span> itertools\r\n>>> <\/span>natuals = itertools.count(1<\/span>)\r\n>>> <\/span>for<\/span> n in<\/span> natuals:\r\n... <\/span>    print(n)\r\n...\r\n1<\/span>\r\n2<\/span>\r\n3<\/span>\r\n...\r\n<\/code><\/pre>\n
\u56e0\u4e3acount()<\/code>\u4f1a\u521b\u5efa\u4e00\u4e2a\u65e0\u9650\u7684\u8fed\u4ee3\u5668\uff0c\u6240\u4ee5\u4e0a\u8ff0\u4ee3\u7801\u4f1a\u6253\u5370\u51fa\u81ea\u7136\u6570\u5e8f\u5217\uff0c\u6839\u672c\u505c\u4e0d\u4e0b\u6765\uff0c\u53ea\u80fd\u6309Ctrl+C<\/code>\u9000\u51fa\u3002<\/p>\n
cycle()<\/code>\u4f1a\u628a\u4f20\u5165\u7684\u4e00\u4e2a\u5e8f\u5217\u65e0\u9650\u91cd\u590d\u4e0b\u53bb\uff1a<\/p>\n
>>> <\/span>import<\/span> itertools\r\n>>> <\/span>cs = itertools.cycle('ABC'<\/span>) # \u6ce8\u610f\u5b57\u7b26\u4e32\u4e5f\u662f\u5e8f\u5217\u7684\u4e00\u79cd<\/span>\r\n>>> <\/span>for<\/span> c in<\/span> cs:\r\n... <\/span>    print(c)\r\n...\r\n'A'<\/span>\r\n'B'<\/span>\r\n'C'<\/span>\r\n'A'<\/span>\r\n'B'<\/span>\r\n'C'<\/span>\r\n...\r\n<\/code><\/pre>\n
\u540c\u6837\u505c\u4e0d\u4e0b\u6765\u3002<\/p>\n
repeat()<\/code>\u8d1f\u8d23\u628a\u4e00\u4e2a\u5143\u7d20\u65e0\u9650\u91cd\u590d\u4e0b\u53bb\uff0c\u4e0d\u8fc7\u5982\u679c\u63d0\u4f9b\u7b2c\u4e8c\u4e2a\u53c2\u6570\u5c31\u53ef\u4ee5\u9650\u5b9a\u91cd\u590d\u6b21\u6570\uff1a<\/p>\n
>>> <\/span>ns = itertools.repeat('A'<\/span>, 3<\/span>)\r\n>>> <\/span>for<\/span> n in<\/span> ns:\r\n... <\/span>    print(n)\r\n...\r\nA\r\nA\r\nA\r\n<\/code><\/pre>\n
\u65e0\u9650\u5e8f\u5217\u53ea\u6709\u5728for<\/code>\u8fed\u4ee3\u65f6\u624d\u4f1a\u65e0\u9650\u5730\u8fed\u4ee3\u4e0b\u53bb\uff0c\u5982\u679c\u53ea\u662f\u521b\u5efa\u4e86\u4e00\u4e2a\u8fed\u4ee3\u5bf9\u8c61\uff0c\u5b83\u4e0d\u4f1a\u4e8b\u5148\u628a\u65e0\u9650\u4e2a\u5143\u7d20\u751f\u6210\u51fa\u6765\uff0c\u4e8b\u5b9e\u4e0a\u4e5f\u4e0d\u53ef\u80fd\u5728\u5185\u5b58\u4e2d\u521b\u5efa\u65e0\u9650\u591a\u4e2a\u5143\u7d20\u3002<\/p>\n
\u65e0\u9650\u5e8f\u5217\u867d\u7136\u53ef\u4ee5\u65e0\u9650\u8fed\u4ee3\u4e0b\u53bb\uff0c\u4f46\u662f\u901a\u5e38\u6211\u4eec\u4f1a\u901a\u8fc7takewhile()<\/code>\u7b49\u51fd\u6570\u6839\u636e\u6761\u4ef6\u5224\u65ad\u6765\u622a\u53d6\u51fa\u4e00\u4e2a\u6709\u9650\u7684\u5e8f\u5217\uff1a<\/p>\n
>>> <\/span>natuals = itertools.count(1<\/span>)\r\n>>> <\/span>ns = itertools.takewhile(lambda<\/span> x: x <= 10<\/span>, natuals)\r\n>>> <\/span>list(ns)\r\n[1<\/span>, 2<\/span>, 3<\/span>, 4<\/span>, 5<\/span>, 6<\/span>, 7<\/span>, 8<\/span>, 9<\/span>, 10<\/span>]\r\n<\/code><\/pre>\n
itertools<\/code>\u63d0\u4f9b\u7684\u51e0\u4e2a\u8fed\u4ee3\u5668\u64cd\u4f5c\u51fd\u6570\u66f4\u52a0\u6709\u7528\uff1a<\/p>\n
chain()<\/h3>\n
chain()<\/code>\u53ef\u4ee5\u628a\u4e00\u7ec4\u8fed\u4ee3\u5bf9\u8c61\u4e32\u8054\u8d77\u6765\uff0c\u5f62\u6210\u4e00\u4e2a\u66f4\u5927\u7684\u8fed\u4ee3\u5668\uff1a<\/p>\n
>>> <\/span>for<\/span> c in<\/span> itertools.chain('ABC'<\/span>, 'XYZ'<\/span>):\r\n... <\/span>    print(c)\r\n# \u8fed\u4ee3\u6548\u679c\uff1a'A' 'B' 'C' 'X' 'Y' 'Z'<\/span>\r\n<\/code><\/pre>\n
groupby()<\/h3>\n
groupby()<\/code>\u628a\u8fed\u4ee3\u5668\u4e2d\u76f8\u90bb\u7684\u91cd\u590d\u5143\u7d20\u6311\u51fa\u6765\u653e\u5728\u4e00\u8d77\uff1a<\/p>\n
>>> <\/span>for<\/span> key, group in<\/span> itertools.groupby('AAABBBCCAAA'<\/span>):\r\n... <\/span>    print(key, list(group))\r\n...\r\nA ['A'<\/span>, 'A'<\/span>, 'A'<\/span>]\r\nB ['B'<\/span>, 'B'<\/span>, 'B'<\/span>]\r\nC ['C'<\/span>, 'C'<\/span>]\r\nA ['A'<\/span>, 'A'<\/span>, 'A'<\/span>]\r\n<\/code><\/pre>\n
\u5b9e\u9645\u4e0a\u6311\u9009\u89c4\u5219\u662f\u901a\u8fc7\u51fd\u6570\u5b8c\u6210\u7684\uff0c\u53ea\u8981\u4f5c\u7528\u4e8e\u51fd\u6570\u7684\u4e24\u4e2a\u5143\u7d20\u8fd4\u56de\u7684\u503c\u76f8\u7b49\uff0c\u8fd9\u4e24\u4e2a\u5143\u7d20\u5c31\u88ab\u8ba4\u4e3a\u662f\u5728\u4e00\u7ec4\u7684\uff0c\u800c\u51fd\u6570\u8fd4\u56de\u503c\u4f5c\u4e3a\u7ec4\u7684key\u3002\u5982\u679c\u6211\u4eec\u8981\u5ffd\u7565\u5927\u5c0f\u5199\u5206\u7ec4\uff0c\u5c31\u53ef\u4ee5\u8ba9\u5143\u7d20'A'<\/code>\u548c'a'<\/code>\u90fd\u8fd4\u56de\u76f8\u540c\u7684key\uff1a<\/p>\n
>>> <\/span>for<\/span> key, group in<\/span> itertools.groupby('AaaBBbcCAAa'<\/span>, lambda<\/span> c: c.upper()):\r\n... <\/span>    print(key, list(group))\r\n...\r\nA ['A'<\/span>, 'a'<\/span>, 'a'<\/span>]\r\nB ['B'<\/span>, 'B'<\/span>, 'b'<\/span>]\r\nC ['c'<\/span>, 'C'<\/span>]\r\nA ['A'<\/span>, 'A'<\/span>, 'a'<\/span>]\r\n<\/code><\/pre>\n
\u5c0f\u7ed3<\/h3>\n
itertools<\/code>\u6a21\u5757\u63d0\u4f9b\u7684\u5168\u90e8\u662f\u5904\u7406\u8fed\u4ee3\u529f\u80fd\u7684\u51fd\u6570\uff0c\u5b83\u4eec\u7684\u8fd4\u56de\u503c\u4e0d\u662flist\uff0c\u800c\u662fIterator<\/code>\uff0c\u53ea\u6709\u7528for<\/code>\u5faa\u73af\u8fed\u4ee3\u7684\u65f6\u5019\u624d\u771f\u6b63\u8ba1\u7b97\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
Python\u7684\u5185\u5efa\u6a21\u5757itertools\u63d0\u4f9b\u4e86\u975e\u5e38\u6709\u7528\u7684\u7528\u4e8e\u64cd\u4f5c\u8fed\u4ee3\u5bf9\u8c61\u7684\u51fd\u6570\u3002 … \u7ee7\u7eed\u9605\u8bfb →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[17],"tags":[29],"_links":{"self":[{"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/posts\/564"}],"collection":[{"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/comments?post=564"}],"version-history":[{"count":1,"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/posts\/564\/revisions"}],"predecessor-version":[{"id":565,"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/posts\/564\/revisions\/565"}],"wp:attachment":[{"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/media?parent=564"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/categories?post=564"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/tags?post=564"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}