Python编程从入门到实践笔记——异常和存储数据

错误。每当发生让Python不知所措的错误时，它都会创建一个异常对象。代码，程序将继续运行；如果你未对异常进行处理，程序将停止，并显示一个traceback，其中包含有关异常的报告。代码块处理的。try-except 代码块让Python执行指定的操作，同时告诉Python发生异常时怎么办。代码块时，即便出现异常，程序也将继续运行：显示你编写的友好的错误消息，而不是令用户迷惑的traceback。

#1.处理ZeroDivisionError异常

print(5/0)

#2.使用try-except 代码块
try:
print(5/0)
except ZeroDivisionError:
print("You can't devide by zero.")

#3.使用异常避免崩溃

#4.else 代码块

依赖于try 代码块成功执行的代码都应放到else 代码块中：

print("Give me two numbers,and I'll divide them.")
print("Enter 'q' to quit.")
while True:
first_number = input("\nFirst number: ")
if first_number == 'q':
break
second_number = input("Second number: ")
try:
answer = int(first_number) / int(second_number)
except ZeroDivisionError:
print("You can't divide by 0!")
else:
print(answer)

#5.处理FileNotFoundError异常
filename = 'alice.txt'

try:
with open(filename) as f_obj:
contents = f_obj.read()
except FileNotFoundError:
msg = "Sorry,the file " + filename + " does not exist."
print(msg)

#6.分析文本
filename = 'alice.txt'
try:
with open(filename) as f_obj:
contents = f_obj.read()
except FileNotFoundError:
msg = "Sorry,the file " + filename + " does not exist."
print(msg)
else:
# 计算文件大致包含多少个单词
words = contents.split()
num_words = len(words)
print("The file " + filename + " has about " + str(num_words) + " words.")

#7.使用多个文件
def count_words(filename):
"""--snip--"""

filenames = ['alice.txt','siddhartha.txt','moby_dick.txt','little_women.txt']
for filename in filenames:
count_words(filename)

#8.失败时一声不吭 pass语句
def count_words(filename):
"""计算一个文件大致包含多少个单词"""
try:
"""--snip--"""
except FileNotFoundError:
pass
else:
"""--snip--"""

#10.4存储数据

1.使用json.dump() 和json.load()

import json

numbers = [2,3,5,7,11,13]
filename = 'numbers.json'
with open(filename,'w') as f_obj:
json.dump(numbers,f_obj)

#2.保存和读取用户生成的数据
import json

username = input("What is your name? ")
filename = 'username.json'
with open(filename,'w') as f_obj:
json.dump(username,f_obj)
print("We'll remember you when you come back," + username + "!")

with open(filename) as f_obj:
username = json.load(f_obj)
print("Welcome back," + username + "!")

Python编程从入门到实践笔记——异常和存储数据

<span style="color: #008000;">print(5/0)

<span style="color: #008000;">依赖于try 代码块成功执行的代码都应放到else 代码块中：

<span style="color: #008000;">1.使用json.dump() 和json.load()

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