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python-hacks:variable-defined [2011/07/05 15:09] (当前版本) |
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+ | ====== Python中如何判断变量是否已经定义 ====== | ||
+ | |||
+ | Python中其实有蛮多方法可以判断一个变量是否已经定义了。 | ||
+ | ===== 方法一:try except ===== | ||
+ | |||
+ | <code python> | ||
+ | def isset(v): | ||
+ | try : | ||
+ | type (eval(v)) | ||
+ | except : | ||
+ | return 0 | ||
+ | else : | ||
+ | return 1 | ||
+ | </code> | ||
+ | |||
+ | 用法: | ||
+ | <code python> | ||
+ | if isset('user_name'): | ||
+ | print 'user_name is defined' | ||
+ | else | ||
+ | print 'user_name is not defined' | ||
+ | </code> | ||
+ | ===== 方法二:使用命名空间 ===== | ||
+ | |||
+ | <code python> | ||
+ | 'varname' in locals().keys() | ||
+ | 'varname' in dir() | ||
+ | </code> | ||
+ | |||