Python基礎知識(三)--基本的異常處理、算術運算符、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'

算術運算符

+    -    *    /    += ...

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
#類型不匹配
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)

* 應該儘量將異常處理模塊放在程序末尾，以保證主要流程儘可能清晰