Python基礎知識(三)–基本的異常處理、算術運算子、輸入/輸出

異常處理

 

  
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' 
 

算術運算子

+ - * / += ...

 

  
seeds = ['sesame', 'sunflower', 'pumpkin'] 
  
seeds += ['poppy'] 
  
print(seeds) 
  
#['sesame', 'sunflower', 'pumpkin', 'poppy'] 
  
#這個時候的運算同seeds.append('poppy')等價 
  
seeds += 2 
  
#TypeError: 'int' object is not iterable 
  
#類型不符 
  
seeds += 'durian' 
  
print(seeds) 
  
#['sesame', 'sunflower', 'pumpkin', 'poppy', 'd', 'u', 'r', 'i', 'a', 'n'] 
  
#不同類型的即便可以執行，也會出現比較奇怪的結果 
  
#這個時候用seeds.append('durian')可得到正確的結果 
 

輸入/輸出

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:") #輸入數字 
  
 if line: #如果非空 
  
 try: 
  
 number = int(line) #轉換成整數 
  
 except ValueError as err: 
  
 print(err) #非整數 
  
 continue 
  
 total += number 
  
 count += 1 
  
 else: 
  
 break 
  
 
  
if count: 
  
 print("count = ", count, "total = ", total, "mean = ", total / count) 
 

* 應該盡量將異常處理模組放在程式末尾，以保證主要流程儘可能清晰