{"id":566,"date":"2017-07-09T16:54:55","date_gmt":"2017-07-09T08:54:55","guid":{"rendered":"https:\/\/9dream.me\/?p=566"},"modified":"2017-07-09T16:54:55","modified_gmt":"2017-07-09T08:54:55","slug":"python%e5%9f%ba%e7%a1%807-8-contextlib","status":"publish","type":"post","link":"https:\/\/9dream.me\/python%e5%9f%ba%e7%a1%807-8-contextlib\/","title":{"rendered":"Python\u57fa\u78407.8-contextlib"},"content":{"rendered":"
\n

\u5728Python\u4e2d\uff0c\u8bfb\u5199\u6587\u4ef6\u8fd9\u6837\u7684\u8d44\u6e90\u8981\u7279\u522b\u6ce8\u610f\uff0c\u5fc5\u987b\u5728\u4f7f\u7528\u5b8c\u6bd5\u540e\u6b63\u786e\u5173\u95ed\u5b83\u4eec\u3002\u6b63\u786e\u5173\u95ed\u6587\u4ef6\u8d44\u6e90\u7684\u4e00\u4e2a\u65b9\u6cd5\u662f\u4f7f\u7528try...finally<\/code>\uff1a<\/p>\n

try<\/span>:\r\n    f = open('\/path\/to\/file'<\/span>, 'r'<\/span>)\r\n    f.read()\r\nfinally<\/span>:\r\n    if<\/span> f:\r\n        f.close()\r\n<\/code><\/pre>\n
\u5199try...finally<\/code>\u975e\u5e38\u7e41\u7410\u3002Python\u7684with<\/code>\u8bed\u53e5\u5141\u8bb8\u6211\u4eec\u975e\u5e38\u65b9\u4fbf\u5730\u4f7f\u7528\u8d44\u6e90\uff0c\u800c\u4e0d\u5fc5\u62c5\u5fc3\u8d44\u6e90\u6ca1\u6709\u5173\u95ed\uff0c\u6240\u4ee5\u4e0a\u9762\u7684\u4ee3\u7801\u53ef\u4ee5\u7b80\u5316\u4e3a\uff1a<\/p>\n
with<\/span> open('\/path\/to\/file'<\/span>, 'r'<\/span>) as<\/span> f:\r\n    f.read()\r\n<\/code><\/pre>\n
\u5e76\u4e0d\u662f\u53ea\u6709open()<\/code>\u51fd\u6570\u8fd4\u56de\u7684fp\u5bf9\u8c61\u624d\u80fd\u4f7f\u7528with<\/code>\u8bed\u53e5\u3002\u5b9e\u9645\u4e0a\uff0c\u4efb\u4f55\u5bf9\u8c61\uff0c\u53ea\u8981\u6b63\u786e\u5b9e\u73b0\u4e86\u4e0a\u4e0b\u6587\u7ba1\u7406\uff0c\u5c31\u53ef\u4ee5\u7528\u4e8ewith<\/code>\u8bed\u53e5\u3002<\/p>\n
\u5b9e\u73b0\u4e0a\u4e0b\u6587\u7ba1\u7406\u662f\u901a\u8fc7__enter__<\/code>\u548c__exit__<\/code>\u8fd9\u4e24\u4e2a\u65b9\u6cd5\u5b9e\u73b0\u7684\u3002\u4f8b\u5982\uff0c\u4e0b\u9762\u7684class\u5b9e\u73b0\u4e86\u8fd9\u4e24\u4e2a\u65b9\u6cd5\uff1a<\/p>\n
class<\/span> Query<\/span>(object)<\/span>:<\/span>\r\n\r\n    def<\/span> __init__<\/span>(self, name)<\/span>:<\/span>\r\n        self.name = name\r\n\r\n    def<\/span> __enter__<\/span>(self)<\/span>:<\/span>\r\n        print('Begin'<\/span>)\r\n        return<\/span> self\r\n\r\n    def<\/span> __exit__<\/span>(self, exc_type, exc_value, traceback)<\/span>:<\/span>\r\n        if<\/span> exc_type:\r\n            print('Error'<\/span>)\r\n        else<\/span>:\r\n            print('End'<\/span>)\r\n\r\n    def<\/span> query<\/span>(self)<\/span>:<\/span>\r\n        print('Query info about %s...'<\/span> % self.name)\r\n<\/code><\/pre>\n
\u8fd9\u6837\u6211\u4eec\u5c31\u53ef\u4ee5\u628a\u81ea\u5df1\u5199\u7684\u8d44\u6e90\u5bf9\u8c61\u7528\u4e8ewith<\/code>\u8bed\u53e5\uff1a<\/p>\n
with<\/span> Query('Bob'<\/span>) as<\/span> q:\r\n    q.query()\r\n<\/code><\/pre>\n
@contextmanager<\/h3>\n
\u7f16\u5199__enter__<\/code>\u548c__exit__<\/code>\u4ecd\u7136\u5f88\u7e41\u7410\uff0c\u56e0\u6b64Python\u7684\u6807\u51c6\u5e93contextlib<\/code>\u63d0\u4f9b\u4e86\u66f4\u7b80\u5355\u7684\u5199\u6cd5\uff0c\u4e0a\u9762\u7684\u4ee3\u7801\u53ef\u4ee5\u6539\u5199\u5982\u4e0b\uff1a<\/p>\n
from<\/span> contextlib import<\/span> contextmanager\r\n\r\nclass<\/span> Query<\/span>(object)<\/span>:<\/span>\r\n\r\n    def<\/span> __init__<\/span>(self, name)<\/span>:<\/span>\r\n        self.name = name\r\n\r\n    def<\/span> query<\/span>(self)<\/span>:<\/span>\r\n        print('Query info about %s...'<\/span> % self.name)\r\n\r\n@contextmanager<\/span>\r\ndef<\/span> create_query<\/span>(name)<\/span>:<\/span>\r\n    print('Begin'<\/span>)\r\n    q = Query(name)\r\n    yield<\/span> q\r\n    print('End'<\/span>)\r\n<\/code><\/pre>\n
@contextmanager<\/code>\u8fd9\u4e2adecorator\u63a5\u53d7\u4e00\u4e2agenerator\uff0c\u7528yield<\/code>\u8bed\u53e5\u628awith ... as var<\/code>\u628a\u53d8\u91cf\u8f93\u51fa\u51fa\u53bb\uff0c\u7136\u540e\uff0cwith<\/code>\u8bed\u53e5\u5c31\u53ef\u4ee5\u6b63\u5e38\u5730\u5de5\u4f5c\u4e86\uff1a<\/p>\n
with<\/span> create_query('Bob'<\/span>) as<\/span> q:\r\n    q.query()\r\n<\/code><\/pre>\n
\u5f88\u591a\u65f6\u5019\uff0c\u6211\u4eec\u5e0c\u671b\u5728\u67d0\u6bb5\u4ee3\u7801\u6267\u884c\u524d\u540e\u81ea\u52a8\u6267\u884c\u7279\u5b9a\u4ee3\u7801\uff0c\u4e5f\u53ef\u4ee5\u7528@contextmanager<\/code>\u5b9e\u73b0\u3002\u4f8b\u5982\uff1a<\/p>\n
@contextmanager<\/span>\r\ndef<\/span> tag<\/span>(name)<\/span>:<\/span>\r\n    print(\"<%s>\"<\/span> % name)\r\n    yield<\/span>\r\n    print(\"<\/%s>\"<\/span> % name)\r\n\r\nwith<\/span> tag(\"h1\"<\/span>):\r\n    print(\"hello\"<\/span>)\r\n    print(\"world\"<\/span>)\r\n<\/code><\/pre>\n
\u4e0a\u8ff0\u4ee3\u7801\u6267\u884c\u7ed3\u679c\u4e3a\uff1a<\/p>\n
<h1<\/span>><\/span>\r\nhello\r\nworld\r\n<\/h1<\/span>><\/span>\r\n<\/code><\/pre>\n
\u4ee3\u7801\u7684\u6267\u884c\u987a\u5e8f\u662f\uff1a<\/p>\n
    \n
  1. with<\/code>\u8bed\u53e5\u9996\u5148\u6267\u884cyield<\/code>\u4e4b\u524d\u7684\u8bed\u53e5\uff0c\u56e0\u6b64\u6253\u5370\u51fa<h1><\/code>\uff1b<\/li>\n
  2. yield<\/code>\u8c03\u7528\u4f1a\u6267\u884cwith<\/code>\u8bed\u53e5\u5185\u90e8\u7684\u6240\u6709\u8bed\u53e5\uff0c\u56e0\u6b64\u6253\u5370\u51fahello<\/code>\u548cworld<\/code>\uff1b<\/li>\n
  3. \u6700\u540e\u6267\u884cyield<\/code>\u4e4b\u540e\u7684\u8bed\u53e5\uff0c\u6253\u5370\u51fa<\/h1><\/code>\u3002<\/li>\n<\/ol>\n
    \u56e0\u6b64\uff0c@contextmanager<\/code>\u8ba9\u6211\u4eec\u901a\u8fc7\u7f16\u5199generator\u6765\u7b80\u5316\u4e0a\u4e0b\u6587\u7ba1\u7406\u3002<\/p>\n
    @closing<\/h3>\n
    \u5982\u679c\u4e00\u4e2a\u5bf9\u8c61\u6ca1\u6709\u5b9e\u73b0\u4e0a\u4e0b\u6587\uff0c\u6211\u4eec\u5c31\u4e0d\u80fd\u628a\u5b83\u7528\u4e8ewith<\/code>\u8bed\u53e5\u3002\u8fd9\u4e2a\u65f6\u5019\uff0c\u53ef\u4ee5\u7528closing()<\/code>\u6765\u628a\u8be5\u5bf9\u8c61\u53d8\u4e3a\u4e0a\u4e0b\u6587\u5bf9\u8c61\u3002\u4f8b\u5982\uff0c\u7528with<\/code>\u8bed\u53e5\u4f7f\u7528urlopen()<\/code>\uff1a<\/p>\n
    from<\/span> contextlib import<\/span> closing\r\nfrom<\/span> urllib.request import<\/span> urlopen\r\n\r\nwith<\/span> closing(urlopen('https:\/\/www.python.org'<\/span>)) as<\/span> page:\r\n    for<\/span> line in<\/span> page:\r\n        print(line)\r\n<\/code><\/pre>\n
    closing<\/code>\u4e5f\u662f\u4e00\u4e2a\u7ecf\u8fc7@contextmanager\u88c5\u9970\u7684generator\uff0c\u8fd9\u4e2agenerator\u7f16\u5199\u8d77\u6765\u5176\u5b9e\u975e\u5e38\u7b80\u5355\uff1a<\/p>\n
    @contextmanager<\/span>\r\ndef<\/span> closing<\/span>(thing)<\/span>:<\/span>\r\n    try<\/span>:\r\n        yield<\/span> thing\r\n    finally<\/span>:\r\n        thing.close()\r\n<\/code><\/pre>\n
    \u5b83\u7684\u4f5c\u7528\u5c31\u662f\u628a\u4efb\u610f\u5bf9\u8c61\u53d8\u4e3a\u4e0a\u4e0b\u6587\u5bf9\u8c61\uff0c\u5e76\u652f\u6301with<\/code>\u8bed\u53e5\u3002<\/p>\n
    @contextlib<\/code>\u8fd8\u6709\u4e00\u4e9b\u5176\u4ed6decorator\uff0c\u4fbf\u4e8e\u6211\u4eec\u7f16\u5199\u66f4\u7b80\u6d01\u7684\u4ee3\u7801\u3002<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"
    \u5728Python\u4e2d\uff0c\u8bfb\u5199\u6587\u4ef6\u8fd9\u6837\u7684\u8d44\u6e90\u8981\u7279\u522b\u6ce8\u610f\uff0c\u5fc5\u987b\u5728\u4f7f\u7528\u5b8c\u6bd5\u540e\u6b63\u786e\u5173\u95ed\u5b83\u4eec\u3002\u6b63 … \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\/566"}],"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=566"}],"version-history":[{"count":1,"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/posts\/566\/revisions"}],"predecessor-version":[{"id":567,"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/posts\/566\/revisions\/567"}],"wp:attachment":[{"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/media?parent=566"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/categories?post=566"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/9dream.me\/wp-json\/wp\/v2\/tags?post=566"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}