Python 小知识

1. if name == 'main' 作用

简单来说，就是这个语句只有在这个文件自己被执行的时候才会true执行，被别的文件引用的时候就不会执行。从而方便测试。
浅析python 中name = 'main' 的作用

2. GUI 之 Tkinter

例子

3.print和sys.stdout.write

print(obj)内部就是sys.stdout.\write(obj+'\n')

4.单引号和双引号

s1 = 'string'
s2 = "string"
s3 = '"' #被单引号包含时双引号不用转义
s4 = "'" #被双引号包含时单引号不用转义

5.With语句

with 语句执行紧跟着的对象的enter()方法，然后将返回值赋予as部分，最后执行exit()方法。

class Sample:
    def __enter__(self):
        return self

    def __exit__(self, type, value, trace):
        print "type:", type
        print "value:",  value
        print "trace:",  trace

    def do_something(self):
        bar = 1/0
        return bar + 10

with Sample() as sample:
    sample.do_something()

输出：

type: <type 'exceptions.ZeroDivisionError'>
value: integer division or modulo by zero
trace: <traceback object at 0x1004a8128>
Traceback
(most recent call last):
File "./with_example02.py",
line 19, in <module>
  sample.do_something()
File "./with_example02.py",
  line 15, in do_something
  bar = 1/0
ZeroDivisionError:
  integer division or modulo  by zero

6. 共享类变量

class Counter:
    count = 0    
    def __init__(self):
        print("Do a test")
    def plus(self):
        self.count = self.count + 1
        print(self.count)
a = counter()
b = counter()
a.plus()
b.plus()
// 1 
// 1


class Counter:
    count = 0    
    def __init__(self):
        print("Do a test")
    def plus(self):
        Counter.count = Counter.count + 1
        print(Counter.count)
a = counter()
b = counter()
a.plus()
b.plus()
// 1 
// 2