python基础--文件与异常

python基础导航✨✨✨

从文件中读取数据

1
2
3

with open('pi.txt') as file_object:
    contents = file_object.read()
    print(contents)

3.1415926535  
  8979323846  
  2643383279

文件路径

绝对路径
相对路径（可以使用r""原始字符串、或者使用双反斜杠\\替代单斜杠\）

file_name = r"pi.txt"
with open(file_name) as file_object:
    contents = file_object.read()
    print(contents)

3.1415926535  
  8979323846  
  2643383279

# 逐行读取数据
with open(file_name) as file_object:
    for line in file_object:
        print(line)

3.1415926535  

  8979323846  

  2643383279

readlines()从文件中读取每一行，并将其存储在一个列表中

with open(file_name) as file_object: 
    lines = file_object.readlines() 

print(lines)

['3.1415926535  \n', '  8979323846  \n', '  2643383279']

'''
使用文件的内容 
'''
with open(file_name) as file_object: 
    lines = file_object.readlines() 

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

print(pi_string)
print(len(pi_string))

3.141592653589793238462643383279
32

'''
圆周率值中包含你的生日吗 
'''
file_name = 'pi_10000.txt'
with open(file_name) as file_object: 
    lines = file_object.readlines() 

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

birthday = input("Enter your birthday, in the form mmddyy:")
if birthday in pi_string:
    print("Your birthday appears in the first million digits of pi!") 
else: 
    print("Your birthday does not appear in the first million digits of pi.")

Enter your birthday, in the form mmddyy: 040413

Your birthday does not appear in the first million digits of pi.

写入文件

读取模式r、写入模式w、附加模式a或让你能够读取和写入文件的模式r+

filename = 'programming.txt'

with open(filename, 'w') as file_object:
    file_object.write("I love programming.")

异常

异常合集Expection 万物皆可用

处理ZeroDivisionError异常

1	print(5/0)

---------------------------------------------------------------------------

ZeroDivisionError                         Traceback (most recent call last)

Cell In[13], line 1
----> 1 print(5/0)

ZeroDivisionError: division by zero

使用try-except代码块

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

You can't divide by zero!

else 代码块

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("The result is:", answer)

Give me two numbers, and I'll divide them.
Enter 'q' to quit.

First number:  5
Second number:  0

You can't divide by 0!
  
First number:  5
Second number:  2

The result is: 2.5

First number:  q

分析文本

1 2	title = "Alice in Wonderland" title.split()

['Alice', 'in', 'Wonderland']

file_name = 'alice1.txt'

try:
    with open(file_name) as f:
        contents = f.read()
except FileNotFoundError:
    msg = "Sorry, the file " + file_name + " does not exist."
    print(msg)
else:
    words = contents.split()
    num_words = len(words)
    print(f"The file {file_name} has about {str(num_words)} words.")

Sorry, the file alice1.txt does not exist.

file_name = 'alice.txt'

try:
    with open(file_name, encoding='utf-8') as f:
        contents = f.read()
except FileNotFoundError:
    msg = "Sorry, the file " + file_name + " does not exist."
    print(msg)
else:
    words = contents.split()
    num_words = len(words)
    print(f"The file {file_name} has about {str(num_words)} words.")

The file alice.txt has about 17868 words.

失败时一声不吭`pass`

file_name = 'alice1.txt'

try:
    with open(file_name) as f:
        contents = f.read()
except FileNotFoundError:
    pass
else:
    words = contents.split()
    num_words = len(words)
    print(f"The file {file_name} has about {str(num_words)} words.")

存储数据

json.dump() 存储数据
json.load() 加载数据

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

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

print(numbers)

[2, 3, 5, 7, 11, 13]

保存和读取用户生成的数据

import json

# 如果以前存储了用户名，就加载它
#  否则，就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 + "!")

What is your name?  kj

We'll remember you when you come back, kj!

重构

重构：代码能够正确地运行，但可做进一步的改进——将代码划分为一系列完成具体工作的函数

import json 

def greet_user():
    """问候用户，并指出其名字"""
    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 + "!") 

greet_user()

Welcome back, kj!

import json 

def get_stored_username():
    """如果存储了用户名，就获取它"""
    filename = 'username.json'
    try:
        with open(filename) as f_obj:
            username = json.load(f_obj)
    except FileNotFoundError:
        return None
    else:
        return username

def get_new_username(): 
    """提示用户输入用户名""" 
    username = input("What is your name? ") 
    filename = 'username.json' 
    with open(filename, 'w') as f_obj: 
        json.dump(username, f_obj) 
    return username 

def greet_user():
    """问候用户，并指出其名字"""
    username = get_stored_username()
    if username:
        print("Welcome back, " + username + "!")
    else:
        username = get_new_username()
        print("We'll remember you when you come back, " + username + "!")

greet_user()