局部变量疑惑，为什么这里的不用 global

[Kuonji]

c = {}

def foo():
	#global c
	c['a'] = 1

执行 foo()后，输出 c，加不加 global,输出都一样 out:{'a': 1}

[n329291362]

LEGB 原则

[TJT]

因为你只是调用了的 a 对象的 __setitem__ 方法，没有对 a 重新赋值，自然也不需要 global。

[Vegetable]

global 是将局部作用域的局部变量,拿到外边去,成为全局变量.
你这个例子是直接操作了全局变量.两回事.

[dangyuluo]

@TJT 是调用了`c`对象的`__setitem__`

[codechaser]

如果只是引用外层变量的话，是不需要 global 的。但是要是涉及到赋值时则需要使用 global，前提是那个全局变量已经被引入到了当前作用域。
```python
def f():
print(s)

#不会出错
s = "foo"
f()

def foo():
s = 100
print(s)

#也不会出错
foo()

def test():
print(s)
#这里会出错
s = 555
print(s)

test()
# local variable 's' referenced before assignment
```

> We only need to use global keyword in a function if we want to do assignments / change them. global is not needed for printing and accessing. Why? Python “ assumes ” that we want a local variable due to the assignment to s inside of f(), so the first print statement throws this error message. Any variable which is changed or created inside of a function is local, if it hasn ’ t been declared as a global variable. To tell Python, that we want to use the global variable, we have to use the keyword “ global ”, as can be seen in the following

[Outliver0]

python 中的可变类型和不可变类型