《python编程从入门到实践》day16

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第十章文件和异常

10.1 从文件中读取数据

10.1.1 读取整个文件

txt文件与程序文件在同一级目录

python 复制代码

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

# 运行结果：
# 3.1415926535
#     8979323846
#

10.1.2 文件路径

python 复制代码

with open('文件路径/Desktop/pi_digits.txt') as file_object:
    contents = file_object.read()
print(contents.rstrip())
# print(contents)

# 运行结果：
# 3.1415926535
#     8979323846
#     2643383279

10.1.3 逐行读取

python 复制代码

filename = 'pi_digits.txt'
with open(filename) as file_object:
    for line in file_object:
        print(line.rstrip())


# 运行结果：
# 3.1415926535
#     8979323846

10.1.4 创建一个包含文件各行内容的列表

python 复制代码

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

print(lines)
for line in lines:
    print(line.rstrip())


# 运行结果：
# ['3.1415926535\n', '    8979323846']
# 3.1415926535
#     8979323846

10.1.5 使用文件的内容

python 复制代码

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

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


print(pi_string)
print(len(pi_string))


# 运行结果：
# 3.14159265358979323846
# 22

10.1.6 包含一百万位的大型文件

python 复制代码

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

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

birthday = input("Enter your birthday")
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!")
print(f"{pi_string[:52]}...")
print(len(pi_string))


# 运行结果：
# Enter your birthday120372
# Your birthday does not appear in the first million digits of pi!
# 3.14159265358979323846264338327950288419716939937510...
# 6554

10.2 写入文件

10.2.1 写入空文件

python 复制代码

filename = 'programming.txt'
with open(filename, 'w', encoding='UTF-8') as file_object:
    file_object.write("I love programming.\n")

10.2.2 写入多行

python 复制代码

filename = 'programming.txt'
with open(filename, 'w', encoding='UTF-8') as file_object:
    file_object.write("I love programming.\n")
    file_object.write("I love creating new games.\n")

10.2.3 附加到文件

python 复制代码

filename = 'programming.txt'
with open(filename, 'w', encoding='UTF-8') as file_object:
    """写入多行"""
    file_object.write("I love programming.\n")
    file_object.write("I love creating new games.\n")

with open(filename, 'a') as file_object:
    """附加到文件"""
    file_object.write("I also love finding meaning in large datasters.\n")
    file_object.write("I love creating apps that can run in a browser.\n")

with open(filename) as file_object:
    """打印文件内容"""
    contents = file_object.read()
    print(contents)

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

10.3 异常

10.3.1 处理ZeroDivisionError异常

python 复制代码

print(5/0)

# 运行结果：
# ZeroDivisionError: division by zero

10.3.2 使用try-except代码块

python 复制代码

try:
    print(5 / 0)
except:
    print("你不能除0运算")

# 运行结果：
# 你不能除0运算

10.3.3 使用异常避免崩溃

python 复制代码

print("给我两个数，我来做除法")
print("按q结束程序")

while True:
    first_number = input('\n请输入第一个数:')
    if first_number == 'q':
        break
    second_number = input("请输入第二个数:")
    if second_number == 'q':
        break
    answer = int(first_number)/int(second_number)
    print(answer)


# 运行结果：   
# 给我两个数，我来做除法
# 按q结束程序
# 
# 请输入第一个数:5
# 请输入第二个数:0
# ZeroDivisionError: division by zero

10.3.4 else代码块

python 复制代码

print("给我两个数，我来做除法")
print("按q结束程序")

while True:
    first_number = input('\n请输入第一个数:')
    if first_number == 'q':
        break
    second_number = input("请输入第二个数:")
    if second_number == 'q':
        break

    try:
        answer = int(first_number)/int(second_number)
    except ZeroDivisionError:
        print("第二个数不能为0")
    else:
        print(answer)


# 运行结果：
# 给我两个数，我来做除法
# 按q结束程序
#
# 请输入第一个数:5
# 请输入第二个数:0
# 第二个数不能为0
#
# 请输入第一个数:2
# 请输入第二个数:4
# 0.5
#
# 请输入第一个数:q
#
# 进程已结束,退出代码0

10.3.5 处理FileNotFoundError异常

python 复制代码

filename = "Alice.txt"
with open(filename,encoding='UTF-8') as f:
    contents = f.read()


# 运行结果：
# FileNotFoundError: [Errno 2] No such file or directory: 'Alice.txt'

10.3.6 分析文本

python 复制代码

filename = "programming.txt"
try:
    with open(filename, encoding='UTF-8') as f:
        contents = f.read()
except:
    print(f'抱歉，名为{filename}的文档不存在')
else:
#     计算文档中含有多少个单词
    print(f"{filename}中的内容：")
    print(contents)
    words = contents.split()
    num_words = len(words)
    print(f"{filename}中有{num_words}个单词")


# 运行结果：
# programming.txt中的内容：
# I love programming.
# I love creating new games.
# I also love finding meaning in large datasters.
# I love creating apps that can run in a browser.
# 
# programming.txt中有26个单词

10.3.7 使用多个文件

python 复制代码

def count_words(filename):
    """计算一个文件中包含多少个单词"""
    try:
        with open(filename, encoding='UTF-8') as f:
            contents = f.read()
    except:
        print(f'抱歉，名为{filename}的文档不存在')
    else:
        print(f"{filename}中的内容：")
        print(f"{contents[:200]}...")
        words = contents.split()
        num_words = len(words)
        print(f"{filename}中有{num_words}个单词")

# filename = 'programming.txt'
# count_words(filename)

filenames = ['programming.txt', 'pi_digits.txt', 'Alice.txt']
for filename in filenames:
    count_words(filename)


# 运行结果：
# programming.txt中的内容：
# I love programming.
# I love creating new games.
# I also love finding meaning in large datasters.
# I love creating apps that can run in a browser.
# ...
# programming.txt中有26个单词
# pi_digits.txt中的内容：
# 3.14159265358979
# 3238462643383279
# 5028841971693993
# 7510582097494459
# 2307816406286208
# 9986280348253421
# 17067982148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954...
# pi_digits.txt中有9个单词
# 抱歉，名为Alice.txt的文档不存在
# 
# 进程已结束,退出代码0

10.3.8 静默失败

pass语句不输出异常报告

python 复制代码

def count_words(filename):
    """计算一个文件中包含多少个单词"""
    try:
        with open(filename, encoding='UTF-8') as f:
            contents = f.read()
    except FileNotFoundError:
       pass
    else:
        print(f"{filename}中的内容：")
        print(f"{contents[:200]}...")
        words = contents.split()
        num_words = len(words)
        print(f"{filename}中有{num_words}个单词")

# filename = 'programming.txt'
# count_words(filename)

filenames = ['programming.txt', 'pi_digits.txt', 'Alice.txt']
for filename in filenames:
    count_words(filename)


# 运行结果：
# programming.txt中的内容：
# I love programming.
# I love creating new games.
# I also love finding meaning in large datasters.
# I love creating apps that can run in a browser.
# ...
# programming.txt中有26个单词
# pi_digits.txt中的内容：
# 3.14159265358979
# 3238462643383279
# 5028841971693993
# 7510582097494459
# 2307816406286208
# 9986280348253421
# 17067982148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954...
# pi_digits.txt中有9个单词