Python编程从入门到实践笔记——异常和存储数据
#coding=gbk
#Python编程从入门到实践笔记——异常和存储数据
#10.3异常
#Python使用被称为异常的特殊对象来管理程序执行期间发生的错误。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。
#如果编写了处理该异常的代码，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。
#异常是使用try-except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。
#使用了try-except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 + "!")