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重新梳理Python基础（9）

2013-03-21 21:27 639 查看

1. list相关的

有一个比较有趣的问题，就是mystuff.append('hello')，python是怎么解释的。这里有段话讲的比较清楚，就不翻译了，直接贴过来。

Python sees you mentioned mystuff and looks up that variable. It might have to look backwards to see if you created with =, look and see if it is a function argument, or maybe it's a global variable. Either way it has to find the mystuff first.

Once it finds mystuff it then hits the . (period) operator and starts to look at variables that are a part of mystuff. Sincemystuff is a list, it knows that mystuff has a bunch of functions.

It then hits append and compares the name "append" to all the ones that mystuff says it owns. If append is in there (it is) then it grabs that to use.

Next Python sees the ( (parenthesis) and realizes, "Oh hey, this should be a function." At this point it calls (aka runs, executes) the function just like normally, but instead it calls the function with an extra argument.

That extra argument is ... mystuff! I know, weird right? But that's how Python works so it's best to just remember it and assume that's alright. What happens then, at the end of all this is a function call that looks like: append(mystuff, 'hello')instead of what you read which is mystuff.append('hello').

>>> class Thing(object):
...     def test(hi):
...             print "hi"
...
>>> a = Thing()
>>> a.test("hello")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: test() takes exactly 1 argument (2 given)

这个错误就很奇怪，上面的解释就解释了这个原因。但是还是不太明白，可能和java不太一样。

贴下代码：

View Code

ten_things = "Apples Oranges Crows Telephone Light Sugar"
print "Wait there's not 10 things in that list, let's fix that."

stuff = ten_things.split(' ')
more_stuff = ["Day", "Night", "Song", "Frisbee", "Corn", "Banana", "Girl", "Boy"]

while len(stuff) != 10:
next_one = more_stuff.pop()
print "Adding: ", next_one
stuff.append(next_one)
print "There's %d items now." % len(stuff)

print "There we go: ", stuff

print "Let's do some things with stuff."

print stuff[1]
print stuff[-1]
print stuff.pop()
print " ".join(stuff)
print "#".join(stuff[3:5])

2. 字典

相当于map。向一个字典中添加和删除元素。

stuff = {'name': 'Zed', 'age': 36, 'height': 6*12+2}
stuff['city'] = "San Francisco"
stuff[1] = "Wow"

del stuff['city']
del stuff[1]

获取元素，有两种方式

print stuff['name']
print stuff['age']

a = stuff.get('Texas', None) #用上面那种方式，如果关键字不存在，会raise异常。用这种方式比较保险，如果关键字不存在'Texas'不存在，那么给a赋值为None。

有序的字典，collection。

3. 模块、类、实例

其实模块和类都和字典类似。看下面：

# dict style
mystuff['apples']

# module style
mystuff.apples()
print mystuff.tangerine

# class style
thing = MyStuff()
thing.apples()
print thing.tangerine

类的方式python运行过程：

Python looks for MyStuff() and sees that it is a class you've defined.

Python crafts an empty object with all the functions you've specified in the class using def.

Python then looks to see if you made a "magic" __init__ function, and if you have it calls that function to initialize your newly created empty object.

In the MyStuff function __init__ I then get this extra variable self which is that empty object Python made for me, and I can set variables on it just like you would with a module, dict, or other object.

In this case, I set self.tangerine to a song lyric and then I've initialized this object.

Now Python can take this newly minted object, and assign it to the thing variable for me to work with.

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