10分钟学会Python［1］

核心提示： 函数使用def关键字，可选参数在必须参数之后出现，10分钟学会Python［1］(4)，并且可以被赋一默认值，对命名参数而言，比如"__spam"（这只是约定，语言中并没有强制规定），参数名参数名被赋一个值，函数可以返回一个元组（打开元组你就可以实现返回多个值）

函数使用def关键字。可选参数在必须参数之后出现，并且可以被赋一默认值。对命名参数而言，参数名参数名被赋一个值。函数可以返回一个元组（打开元组你就可以实现返回多个值）。Lanbda函数是个特例，它由一个表达式构成。参数使用引用传递，但是可变类型（元组，列表，数字，字符串等等）不能被改变。举例如下：

# arg2 and arg3 are optional, they have default values
# if one is not passed (100 and "test", respectively).
def myfunction(arg1, arg2 = 100, arg3 = "test"):
　　return arg3, arg2, arg1
>>>ret1, ret2, ret3 = myfunction("Argument 1", arg3 = "Named argument")
# Using "print" with multiple values prints them all, separated by a space.
>>> print ret1, ret2, ret3
Named argument 100 Argument 1
# Same as def f(x): return x + 1
functionvar = lambda x: x + 1
>>> print functionvar(1)
28. 类

Python部分支持类的多重继承。私有变量和方法可以使用至少两个"_"开始并且至少一个"_"结束来声明，比如"__spam"（这只是约定，语言中并没有强制规定）。我们可以给类的实例赋任意的变量。请看下例：

class MyClass:
　　common = 10
　　def __init__(self):
　　　　self.myvariable = 3
　　def myfunction(self, arg1, arg2):
　　　　return self.myvariable
　　# This is the class instantiation
>>> classinstance = MyClass()
>>> classinstance.myfunction(1, 2)
3
# This variable is shared by all classes.
>>> classinstance2 = MyClass()
>>> classinstance.common
10
>>> classinstance2.common
10
# Note how we use the class name
# instead of the instance.
>>> MyClass.common = 30
>>> classinstance.common
30
>>> classinstance2.common
30
# This will not update the variable on the class,
# instead it will create a new one on the class
# instance and assign the value to that.
>>> classinstance.common = 10
>>> classinstance.common
10
>>> classinstance2.common
30
>>> MyClass.common = 50
# This has not changed, because "common" is
# now an instance variable.
>>> classinstance.common
10
>>> classinstance2.common
50
# This class inherits from MyClass. Multiple
# inheritance is declared as:
# class OtherClass(MyClass1, MyClass2, MyClassN)
class OtherClass(MyClass):
　　def __init__(self, arg1):
　　　　self.myvariable = 3
　　　　print arg1
>>> classinstance = OtherClass("hello")
hello
>>> classinstance.myfunction(1, 2)
3
# This class doesn't have a .test member, but
# we can add one to the instance anyway. Note
# that this will only be a member of classinstance.
>>> classinstance.test = 10
>>> classinstance.test
10