Python基础知识(三)--基本的异常处理、算术运算符、输入/输出

异常处理

try:  
    try_suite  
except exception1 as variable1:  
    exception_suite1  
...  
except exceptionN as variableN:  
    exception_suiteN 

s = input("enter an integer:")  
try:  
    i = int(s)  
    print("valid integer entered:", i)  
except ValueError as err:  
    print(err)  
 
#invalid literal for int() with base 10: '3.5' 

算术运算符

+ - * / += ...

seeds = ['sesame', 'sunflower', 'pumpkin']  
seeds += ['poppy']  
print(seeds)  
#['sesame', 'sunflower', 'pumpkin', 'poppy']  
#这个时候的运算同seeds.append('poppy')等价  
seeds += 2 
#TypeError: 'int' object is not iterable  
#类型不匹配  
seeds += 'durian' 
print(seeds)  
#['sesame', 'sunflower', 'pumpkin', 'poppy', 'd', 'u', 'r', 'i', 'a', 'n']  
#不同类型的即便可以执行，也会出现比较奇怪的结果  
#这个时候用seeds.append('durian')可得到正确的结果 

输入/输出

input()

print()

#!user/bin/env python3  
 
print("Type integers, each followed by Enter; or just Enter to finish")  
 
total = 0 
count = 0 
 
while True:  
    line = input("integer:")    #输入数字  
    if line:                    #如果非空  
        try:  
            number = int(line)  #转换成整数  
        except ValueError as err:  
            print(err)          #非整数  
            continue 
        total += number  
        count += 1 
    else:  
        break 
 
if count:  
    print("count = ", count, "total = ", total, "mean = ", total / count) 

* 应该尽量将异常处理模块放在程序末尾，以保证主要流程尽可能清晰