python小技巧——实时更新

1. 获取所有目录及文件

   for root, dirs, files in os.walk(os.getcwd()):  
       print(root) #当前目录路径  
       print(dirs) #当前路径下所有子目录  
       print(files) #当前路径下所有非目录子文件 

2. 创建文件夹

   isExists=os.path.exists(path)
   if not isExists:
       os.makedirs(path) 
   else:
       print path+'目录已存在'

3. 获取当前路径下所有目录及文件

   import glob    
   glob.glob('C:\\snow\\*.*')  #获取目录[C:\\snow\\]下面所有的文件
   glob.glob('C:\\snow\\*.*')  #获取目录[C:\\snow\\]下面所有.txt文件

4. 数据库连接

   import os, sys
   import pymysql
   class mySql(object):
       def __init__(self):
           self.Conn=None
           self.Cursor=None
   
       def conn(self):
           try:
               self.Conn = pymysql.connect(host='localhost',user='root',passwd='19940512',db='snow')
               self.Cursor = self.Conn.cursor()
           except Exception as e:
               print (e)
   
       def closeconn(self):
           if self.Conn:
               if self.Cursor:
                   self.Cursor.close()
               self.Conn.close()
   
       def getDotInfo(self,table, num, offset,):
           rows=0;
           try:
               self.conn()
               sql='select T_Longitude,T_Latitude,T_Speed,T_Heading,T_TargetID,T_UTCTime from %s limit %r offset %r' % (table, num, offset)
               #print(sql) 
               n = self.Cursor.execute(sql)
               rows = self.Cursor.fetchall()
           except Exception as e:
               pass
           self.closeconn()
           return rows

5. python2与python3兼容方法

   https://www.zhihu.com/question/21653286
   https://zhuanlan.zhihu.com/p/21261875
   https://www.cnblogs.com/zanjiahaoge666/p/7413419.html

6. 常用的模块
   numpy,matplotlib,pandas,scipy —— 数据挖掘与分析的基础
   scikit-learn —— 数据挖掘与分析

7. 字典key与value互换

   >>> a_dict = {'a': 1, 'b': 2, 'c': 3}
   >>> {value:key for key, value in a_dict.items()}
   {1: 'a', 2: 'b', 3: 'c'}

8. 字典赋值

   dict = {‘’a': 1, 'b':1}
   dict['c'] = dict.get('c',0) + 1
   >>>dict
   { 'a':1 ,  'b': 1,  'c':1}

9. 采样(LDA用到了)
   [numpy]random.choice()随机选取内容
   https://blog.csdn.net/autoliuweijie/article/details/51982514