python笔记

• 各进制之间的转换
  http://blog.csdn.net/u012063703/article/details/42609833
• 串口通讯
  http://blog.csdn.net/xhao014/article/details/7640568#

• python调用C库
  http://www.cricode.com/359.html

• chr()、unichr()和ord()

chr()函数用一个范围在range（256）内的（就是0～255）整数作参数，返回一个对应的字符。unichr()跟它一样，只不过返回的是Unicode字符。
ord()函数是chr()函数（对于8位的ASCII字符串）或unichr()函数（对于Unicode对象）的配对函数，它以一个字符（长度为1的字符串）作为参数，返回对应的ASCII数值，或者Unicode数值，如果所给的Unicode字符超出了你的Python定义范围，则会引发一个TypeError的异常。

例子：
十六进制字符串中特定位做位移运算

str2='\xaa\x55\x06\x01\x04\x00\x00\x00\x00\x03'
print (ord(str2[3])&0xff)|((ord(str2[4]) << 8)&0xff00)

int类型的10进制转化为两个16进制

a=-100
print hex((a)&0xff),hex((a >> 8)&0xff)

显示16进制字符串

str1='\xaa\x55\x06\x01\x04\x00\x00\x00\x00\x03'
def hexShow(argv):  
    result = ''  
    hLen = len(argv)  
    for i in xrange(hLen):  
        hvol = ord(argv[i])  
        hhex = '%02x'%hvol  
        result += hhex+' '  
    print 'hexShow:',result

hexShow(str1)

查找子串在父串中的位置

sStr1= 'abcdefg'   
sStr = 'cde'   
print sStr1.find(sStr)

串口通讯的一个例子

#!/usr/bin/env python
from serial.serialutil import SerialException
from serial import Serial
import thread
import time
import sys, traceback
import os
import binascii

def hexShow(argv):  
    result = ''  
    hLen = len(argv)  
    for i in xrange(hLen):  
        hvol = ord(argv[i])  
        hhex = '%02x'%hvol  
        result += hhex+' '  
    print 'hexShow:',result  

class MySerial:
    def __init__(self, port="/dev/ttyUSB0", baudrate=115200, timeout=0.5):   
        self.port = port
        self.baudrate = baudrate
        self.timeout = timeout
        self.encoder_count = 0
        self.writeTimeout = timeout
        self.interCharTimeout = timeout / 30.

        # Keep things thread safe
        self.mutex = thread.allocate_lock()
    def connect(self):
        try:
            print "Connecting to MySerial on port", self.port, "..."
            self.port = Serial(port=self.port, baudrate=self.baudrate, timeout=self.timeout, writeTimeout=self.writeTimeout)
            # The next line is necessary to give the firmware time to wake up.
            time.sleep(1)
            print "connect success!"

        except SerialException:
            print "Serial Exception:"
            print sys.exc_info()
            print "Traceback follows:"
            traceback.print_exc(file=sys.stdout)
            print "Cannot connect to Device!"
            os._exit(1)

    def open(self): 
        ''' Open the serial port.
        '''
        self.port.open()

    def close(self): 
        ''' Close the serial port.
        '''
        self.port.close() 

    def send(self):
        a=100
        str1='\xaa\xbb\xcc\x01\x02\x01\x02\x01\x02\x01\x02'
        print  hexShow(str3)
        self.port.write(str4)
    def recv(self):
        pack=''
        c = self.port.read(16)

        index=c.find('\xaa\xbb')
        if (index!=0):
            d = self.port.read(index)
            pack = c+d
        else:
            pack = c

        print hexShow(pack)
        return (ord(c[index+3])&0xff)|((ord(c[index+4]) << 8)&0xff00), (ord(c[index+5])&0xff)|((ord(c[index+6]) << 8)&0xff00)

if __name__ == '__main__':
      controller = MySerial()
      controller.connect()
      controller.send()
      time.sleep(20)
      val1, val2 = controller.recv()
      controller.close()