Python Tutorial 笔记3

Class

1. Namespace and Scope

 

 

def scope_test():
    def do_local():
        spam = "local spam"
    def do_nonlocal():
        nonlocal spam
        spam = "nonlocal spam"
    def do_global():
        global spam
        spam = "global spam"

    spam = "test spam"
    do_local()
    print("After local assignment:", spam)
    do_nonlocal()
    print("After nonlocal assignment:", spam)
    do_global()
    print("After global assignment:", spam)

scope_test()
print("In global scope:", spam)

#result is:
After local assignment: test spam
After nonlocal assignment: nonlocal spam
After global assignment: nonlocal spam
In global scope: global spam

 

2.  Class definition

 

class MyClass:
    """A simple example class"""

    i = 12345

    def __init__(self, re=0, im=0):
        print('[ENTER] __init__')
        self.data=[]
        self.real = re
        self.image = im
        print('[EXIT] __init__')

    def f(self):
        return 'Hello world'

if __name__ == '__main__':
    x = MyClass()
    print('x is [{0:f}, {1:f}]'.format(x.real, x.image))
    y = MyClass(1.5, -2.7)
    print('y is [{0:f}, {1:f}]'.format(y.real, y.image))

 

 

3.  Iterator

 

 

#! /usr/bin/env python3.0 

class Reserve:
    def __init__(self, data):
        self.data = data
        self.index = len(data)
    def __iter__(self):
        return self
    def __next__(self):
        if self.index == 0:
            raise StopIteration
        self.index = self.index - 1
        return self.data[self.index]

if __name__ == '__main__':
    print([x for x in Reserve('abcdefg')])

 

4.  Generator

 

 

def reverse(data):
    for index in range(len(data)-1, -1, -1):
        yield data[index]

>>> for char in reverse('golf'):
...     print(char)
...
f
l
o
g

 

>>> sum(i*i for i in range(10)) # sum of squares

285