【day 8】python编程：从入门到实践学习笔记-文件和异常（末附答案代码）

第十章 文件和异常

从文件中读取数据

pi_digits.txt
3.1415926535
8979323846
2643383279

file_reader.py
fillename = 'pi_digits.txt'
#读取整个文件
with open(filename) as file_object:
contents = file_object.read()
print(contents.rstrip())

#逐行读取
with open(filename) as file_object:
for line in file_object:
print(line.rstrip())

运行结果：
3.1415926535
8979323846
2643383279
3.1415926535
8979323846
2643383279

open()

with

read()

rstrip()

with

open()

with

with

filename = 'pi_30_digits.txt'
with open(filename) as file_object:
lines = file_object.readlines()

pi_string = ''
for line in lines:
pi_string += line.strip()

print(pi_string)
print(len(pi_string))

运行结果：
3.141592653589793238462643383279
32

写入文件

'r'

'w'

'a'

'r+'

open()

filename = 'programming.txt'
with open(filename, 'w') as file_object:
file_object.write("I love programming.")
file_object.write("I love programming.\n")
file_object.write("I love creating new games.\n")

运行结果：
programming.txt
I love programming.I love programming.
I love creating new games.

write()

filename = 'programming.txt'
with open(filename, 'a') as file_object:
file_object.write("I also love finding meaning in large datasets.\n")
file_object.write("I love creating apps that can run in a browser.\n")

运行结果：
programming.txt
I love programming.I love programming.
I love creating new games.
I also love finding meaning in large datasets.
I love creating apps that can run in a browser.

异常

try-except

try

except

try

except

print(5/0)

运行结果：
Traceback (most recent call last):
File "division.py", line 1, in <module>
print(5/0)
ZeroDivisionError: division by zero

ZeroDivisionError

try:
print(5/0)
except ZeroDivisionError:
print("You can't divide by zero!")

运行结果：
You can't divide by zero!

try-except

try-except

try-except-else

try

else

except

pass

pass

存储数据

json.dump()

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

运行结果：
numbers.json
[2, 3, 5, 7, 11, 13]

json.load()

import json
filename = 'numbers.json'
with open(filename) as f_obj:
numbers = json.load(f_obj)
print(numbers)

运行结果：
[2, 3, 5, 7, 11, 13]

import json
# 如果以前存储了用户名就加载它
# 否则提示用户输入用户名并存储它
filename = 'username.json'
try:
with open(filename) as f_obj:
username = json.load(f_obj)
except FileNotFoundError:
username = input("What is your name? ")
with open(filename, 'w') as f_obj:
json.dump(username, f_obj)
print("We'll remember you when you come back, " + username + "!")
else:
print("Welcome back, " + username + "!")

运行结果：
#如果文件不存在
What is your name? Eric
We'll remember you when you come back, Eric!

#如果文件存在
Welcome back, Eric!