def foo():
a = 1
def bar():
a += 1
print a
if a == 10:
return
bar()
bar()
foo()
结果运行出错
Traceback (most recent call last):
File "temp.py", line 10, in <module>
foo()
File "temp.py", line 9, in foo
bar()
File "temp.py", line 4, in bar
a += 1
UnboundLocalError: local variable 'a' referenced before assignment
修改
def foo():
a = [1]
def bar():
print a
a[0] += 1
if a[0] == 10:
return
bar()
bar()
foo()
运行成功
解释
原因在于Python的数字,字符串是"不可变类型".列表是"可变类型"，而闭包中引用并修改的外部变量需要是可以修改的自由变量。
