Python的基础知识（二）

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python中的函数，文件操作，以及异常的使用：

# -*- coding: utf-8 -*-
#自定义函数
'''
def functionname( parameters ):
   "函数_文档字符串"
   function_suite
   return [expression]		
'''

def printme( str ):
   "打印传入的字符串到标准显示设备上"
   print str
   return

#函数调用
printme("我要调用用户自定义函数!");
printme("再次调用同一函数");


# 可写函数说明
def changeme( mylist ):
   "修改传入的列表"
   mylist.append([1,2,3,4]);
   print "函数内取值: ", mylist
   return
 
# 调用changeme函数
mylist = [10,20,30];
changeme( mylist );
print "函数外取值: ", mylist


#参数
def printme( str ):
   "打印任何传入的字符串"
   print str;
   return;
 
#调用printme函数
printme();

def printme( str ):
   "打印任何传入的字符串"
   print str;
   return;
 
#调用printme函数
printme( str = "My string");


def printinfo( name, age ):
   "打印任何传入的字符串"
   print "Name: ", name;
   print "Age ", age;
   return;
 
#调用printinfo函数
printinfo( age=50, name="miki" );


def printinfo( name, age = 35 ):
   "打印任何传入的字符串"
   print "Name: ", name;
   print "Age ", age;
   return;
 
#调用printinfo函数
printinfo( age=50, name="miki" );
printinfo( name="miki" );

#不定长参数
'''
def functionname([formal_args,] *var_args_tuple ):
   "函数_文档字符串"
   function_suite
   return [expression]
'''
def printinfo( arg1, *vartuple ):
   "打印任何传入的参数"
   print "输出: "
   print arg1
   for var in vartuple:
      print var
   return;
 
# 调用printinfo 函数
printinfo( 10 );
printinfo( 70, 60, 50 );


#匿名函数
'''
lambda [arg1 [,arg2,.....argn]]:expression
'''

sum = lambda arg1, arg2: arg1 + arg2;
# 调用sum函数
print "相加后的值为 : ", sum( 10, 20 )
print "相加后的值为 : ", sum( 20, 20 )


#return语句
def sum( arg1, arg2 ):
   # 返回2个参数的和."
   total = arg1 + arg2
   print "函数内 : ", total
   return total;
 
# 调用sum函数
total = sum( 10, 20 );
print "函数外 : ", total 


#变量的作用范围
total = 0; # 这是一个全局变量
# 可写函数说明
def sum( arg1, arg2 ):
   #返回2个参数的和."
   total = arg1 + arg2; # total在这里是局部变量.
   print "函数内是局部变量 : ", total
   return total;
 
#调用sum函数
sum( 10, 20 );
print "函数外是全局变量 : ", total 


#键盘输入
str = raw_input("Please enter:");
print "你输入的内容是: ", str

str = input("Please enter:");
print "你输入的内容是: ", str

#打开与关闭文件
# 打开一个文件
fo = open("foo.txt", "wb")
print "文件名: ", fo.name
print "是否已关闭 : ", fo.closed
print "访问模式 : ", fo.mode
print "末尾是否强制加空格 : ", fo.softspace


# 打开一个文件
fo = open("foo.txt", "wb")
print "文件名: ", fo.name
fo.close()

# 打开一个文件
fo = open("foo.txt", "wb")
fo.write( "www.runoob.com!\nVery good site!\n");
 
# 关闭打开的文件
fo.close()


# 打开一个文件
fo = open("foo.txt", "r+")
str = fo.read(10);
print "读取的字符串是 : ", str
# 关闭打开的文件
fo.close()


# 打开一个文件
fo = open("foo.txt", "r+")
str = fo.read(10);
print "读取的字符串是 : ", str
 
# 查找当前位置
position = fo.tell();
print "当前文件位置 : ", position
 
# 把指针再次重新定位到文件开头
position = fo.seek(0, 0);
str = fo.read(10);
print "重新读取字符串 : ", str
# 关闭打开的文件
fo.close()

import os
 
# 重命名文件test1.txt到test2.txt。
os.rename( "test1.txt", "test2.txt" )


import os
 
# 删除一个已经存在的文件test2.txt
os.remove("test2.txt")



#异常处理
try:
   fh = open("testfile", "w")
   fh.write("This is my test file for exception handling!!")
except IOError:
   print "Error: can\'t find file or read data"
else:
   print "Written content in the file successfully"
   fh.close()


try:
   fh = open("testfile", "r")
   fh.write("This is my test file for exception handling!!")
except IOError:
   print "Error: can\'t find file or read data"
else:
   print "Written content in the file successfully"


try:
   fh = open("testfile", "w")
   fh.write("This is my test file for exception handling!!")
finally:
   print "Error: can\'t find file or read data"


try:
   fh = open("testfile", "w")
   try:
      fh.write("This is my test file for exception handling!!")
   finally:
      print "Going to close the file"
      fh.close()
except IOError:
   print "Error: can\'t find file or read data"


def temp_convert(var):
   try:
      return int(var)
   except ValueError, Argument:
      print "The argument does not contain numbers\n", Argument

# Call above function here.
temp_convert("xyz");


#异常触发
def functionName( level ):
   if level < 1:
      raise "Invalid level!", level
      # The code below to this would not be executed
      # if we raise the exception

try:
   Business Logic here...
except "Invalid level!":
   Exception handling here...
else:
   Rest of the code here...

#自定义异常
class Networkerror(RuntimeError):
   def __init__(self, arg):
      self.args = arg

try:
   raise Networkerror("Bad hostname")
except Networkerror,e:
   print e.args

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