Python是一种面向对象的开发语言,在函数中使用全局变量,一般应作全局变量说明,只有在函数内经过说明的全局变量才能使用,下面介绍下Python全局变量有关
问题。
应该尽量避免使用Python全局变量。不同的模块都可以自由的访问全局变量,可能会导致全局变量的不可预知性。对全局变量,如果程序员甲修改了_a的值,这时可能导 致程序中的错误。这种错误是很难发现和更正的。
全局变量降低了函数或模块之间的通用性,不同的函数或模块都要依赖于全局变量。同样,全局变量降低了代码的可读性,阅读者可能并不知道调用的某个变量是全局变量。 但是某些时候,Python全局变量能够解决局部变量所难以解决的问题。事物要一分为二。 python;里面全局变量有两种灵活的用法:
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<span class="hljs-id">#gl</span><span class="hljs-class">.py</span> gl_1 = <span class="hljs-string">'hello'</span> gl_2 = <span class="hljs-string">'world'</span> 在其它模块中使用 <span class="hljs-id">#a</span><span class="hljs-class">.py</span> import gl def <span class="hljs-function"><span class="hljs-title">hello_world</span><span class="hljs-params">()</span></span> print gl<span class="hljs-class">.gl_1</span>, gl<span class="hljs-class">.gl_2</span> <span class="hljs-id">#b</span><span class="hljs-class">.py</span> import gl def <span class="hljs-function"><span class="hljs-title">fun1</span><span class="hljs-params">()</span></span> gl<span class="hljs-class">.gl_1</span> = <span class="hljs-string">'Hello'</span> gl<span class="hljs-class">.gl_2</span> = <span class="hljs-string">'World'</span> def <span class="hljs-function"><span class="hljs-title">modifyConstant</span><span class="hljs-params">()</span></span> : global CONSTANT print CONSTANT CONSTANT += <span class="hljs-number">1</span> return <span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">'__main__'</span> : <span class="hljs-function"><span class="hljs-title">modifyConstant</span><span class="hljs-params">()</span></span> print CONSTANT |
1 声明法
在文件开头声明Python全局变量variable, 在具体函数中使用该变量时,需要事先声明 global; variabl e;,否则系统将该变量视为局部变量。 CONSTANT; = 0; (将全局变量大写便于识别)
2模块法(推荐)
,推荐!
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<span class="hljs-id">#gl</span><span class="hljs-class">.py</span> gl_1 = <span class="hljs-string">'hello'</span> gl_2 = <span class="hljs-string">'world'</span> 在其它模块中使用 <span class="hljs-id">#a</span><span class="hljs-class">.py</span> import gl def <span class="hljs-function"><span class="hljs-title">hello_world</span><span class="hljs-params">()</span></span> print gl<span class="hljs-class">.gl_1</span>, gl<span class="hljs-class">.gl_2</span> <span class="hljs-id">#b</span><span class="hljs-class">.py</span> import gl def <span class="hljs-function"><span class="hljs-title">fun1</span><span class="hljs-params">()</span></span> gl<span class="hljs-class">.gl_1</span> = <span class="hljs-string">'Hello'</span> gl<span class="hljs-class">.gl_2</span> = <span class="hljs-string">'World'</span> def <span class="hljs-function"><span class="hljs-title">modifyConstant</span><span class="hljs-params">()</span></span> : global CONSTANT print CONSTANT CONSTANT += <span class="hljs-number">1</span> return <span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">'__main__'</span> : <span class="hljs-function"><span class="hljs-title">modifyConstant</span><span class="hljs-params">()</span></span> print CONSTANT |
