python学习--locals globals
locals() and globals()
locals()和globals()是python的两个内置函数，它们提供了基于dictionary的访问局部和全局变量的方式。
locals()返回一个名字/值对的dictionary。这个dictionary的键字是字符串形式的变量名字，diction的值是变量的实际值。
In [12]: def func(arg):
...: num = 90
...: print locals()
...: print locals()['arg']
...:
In [13]: func('hello')
{'num': 90, 'arg': 'hello'}
hello
globals()函数则返回包含全局变量的dictionary，在下例中，operation()函数根据oper变量的值自动调用相应的全局函数：
In [3]: def plus(a,b):
...: return a+b
...:
In [4]: def minus(a,b):
...: return a-b
...:
In [5]: def operation(oper,a,b):
...: oper = 'plus' if oper=='+' else 'minus'
...: return globasl()[oper](a,b)
...:
In [7]: def operation(oper,a,b):
...: oper = 'plus' if oper=='+' else 'minus'
...: return globals()[oper](a,b)
...:
In [8]: operation('+',2,3)
Out[8]: 5
In [9]: operation('-',2,3)
Out[9]: -1
locals是只读的，globals不是
In [15]: def func():
...: num = 1
...: print locals()
...: locals()['num'] = 3 #无法修改num
...: print "num =",num
...:
In [16]: func()
{'num': 1}
num = 1
In [18]: x = 7
In [19]: print "x =",x
x = 7
In [20]: globals()["x"] = 8 #可以修改x
In [21]: print "x =",x
x = 8
