变量的类型

python是一门动态语言，使用变量时无需预先声明变量的类型，变量可以指向（引用）任何类型的对象

获取类型脚本

➜  python-manual cat var/type.py
import types

for m in dir(types):
    if "Type" in m:
        print m

常见类型说明

变量类型判断

>>> import types
>>> s = '你好'
>>> type(s) == str
True
>>> type(s) == types.StringType
True
>>> type(s) == types.UnicodeType
False
>>> isinstance(s, basestring)
True

>>> u = u'你好'
>>> type(u) == types.StringType
False
>>> type(u) == unicode
True
>>> type(u) == types.UnicodeType
True
>>> isinstance(u, basestring)
True

type 判断会有坑， isinstance 判断更加准确，参见字符序列相关的字节和字符章节

变量的作用域

变量的作用域演示

不同作用域的变量的输出

➜  python-manual cat var/scope.py
var = 'global'


class Var(object):
    var = "class"

    def __init__(self):
        self.var = "instance"

    def test(self):
        var = "method"

        print var
        print self.var

    print var

obj = Var()
obj.test()
print var
test = Var.test
test()

➜  python-manual python var/scope.py
class
method
instance
global
Traceback (most recent call last):
  File "var/scope.py", line 22, in <module>
    test()
TypeError: unbound method test() must be called with Var instance as first argument (got nothing instead)

不同作用域的变量的修改

➜  python-manual cat var/scope.py   
var = 'global'


class Var(object):
    var = "class"

    def __init__(self):
        self.var = "instance"

    def test(self):
        global var
        var = "update_global"

        self.__class__.var = "update_class"
        self.var = "update_instance"


obj = Var()
print var
print Var.var
print obj.var

obj.test()

print var
print Var.var
print obj.var

➜  python-manual python var/scope.py
global
class
instance
update_global
update_class
update_instance

修改全局变量需要global标识，否则就是定义一个同名的局部变量