python出错:local variable XXX referenced before assignment
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出错:局部变量XXX在定义前被引用
如上在多次调用函数时使用返回的值bestThreshVal 时,提示local variable bestThreshVal referenced before assignment。
原因是,在这个被调用函数中,bestThreshVal 是在if 条件语句中得到的一个局部值,并返回。应该在for 循环外定义bestThreshVal 一个初值。
如下简单例子:
t = 2
def printResult(name):
if t== 3:
print name
t= 24
printResult(“xiaoQiang”)
那么就会报如上的错误local variable ‘t’ referenced before assignment。
原因:在python的函数中和全局同名的变量,如果你有修改变量的值就会变成局部变量,在修改之前对该变量的引用自然就会出现没定义这样的错误了,如果确定要引用全局变量,并且要对它修改,必须加上global关键字。
t = 2
def printResult(name):
global t
if t== 3:
print name
t= 24
printResult(“xiaoQiang”)
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