异常

'''
try:
    可能出现异常的代码
except:
    若出现异常执行的代码
'''

try:
    f = open("D:/linux.txt", "r", encoding="utf-8")
    f.readlines()
except:
    print("出现异常了，文件不存在，更换模式w")
    # f = open("D:/linux.txt", "w", encoding="utf-8")

捕获指定异常

'''
try:
    print(name)
except NameError as e:
    print('name变量名未定义错误')
'''

try:
    print(name)
except NameError as e:
    print(e)

捕获多个异常

'''
try:
    print(1/0)
except (NameError, ZeroDivisionError):
    print('name变量名未定义错误')
'''

try:
    print(1 / 0)  # 先捕获
    print(name)
except (NameError, ZeroDivisionError) as e:
    print(e)

捕获所有异常

try:
    print(age)
except Exception as e:
    print(e)

异常else

try:
    print(1)
except Exception as e:
    print(e)
else:
    print("执行else语句，无异常")

finally：无论有无异常都会执行此语句

try:
    print(gender)
except Exception as e:
    print(e)
else:
    print("执行else语句，无异常")
finally:
    print("有无异常都执行finally语句")

包机制

此写法表示本文件可执行，导包调用模块时不执行

if __name__ == "__main__":
    print(1)

打开控制台，指令：pip install 包名

import numpy as np  # 科学计算

e = np.e
print(e)

import pandas as pd  # 数据分析

案例

包结构

模块str_util

# 字符串工具
def str_reverse(s):
    """
    字符串反转
    :param s:原字符串
    :return: 反转后字符串
    """
    return s[::-1]


def substr(s, x, y):
    """
    字符串切片
    :param s:传入字符串
    :param x: 下标
    :param y: 下标
    :return: 被切片字符串
    """
    return s[x:y]


if __name__ == '__main__':
    print(f"字符串逆转后：{str_reverse('java')}")
    print(f"字符串切片后：{substr('java', 0, 3)}")

测试

模块file_util

# 文件处理工具
def print_file_info(file_name):
    """
    读文件内容输出控制台
    :param file_name: 文件路径
    :return: None
    """
    f = None
    try:
        f = open(file_name, "r", encoding="utf-8")
        # lines = f.readlines()
        content = f.read()
        print(content)
    except Exception as e:
        print(f"异常：{e}")
    finally:
        if f:  # 若文件不存在，f=None，if语句中，None表示False，则不会执行f.close()；若文件存在，if f为True，则顺利执行f.close()
            f.close()


def append_to_file(file_name, data):
    """
    向文件追加内容
    :param file_name:文件路径
    :param data: 追加内容
    :return: None
    """
    f = open(file_name, "a", encoding="utf-8")
    f.write(data)
    f.close()


if __name__ == '__main__':
    print_file_info("D:/bill.txt33")
    append_to_file("D:/append.txt", "\naaaabvbbbvvvv")
    print_file_info("D:/append.txt")

测试

注意导包及其调用方法

str1 = my_utils.str_util.str_reverse('TENET')
print("逆转字符串'TENET'：", str1)

str2 = my_utils.str_util.substr('123344556', 3, 6)
print("截串：", str2)

print("文件不存在，异常：")
my_utils.file_util.print_file_info("D:/ttt.txt")

print("追加：")
my_utils.file_util.append_to_file("D:/append.txt", "\t追加：塞尔达传说")

print("文件存在，输出文件内容：")
my_utils.file_util.print_file_info("D:/append.txt")