Python如何单独捕获Errno13权限拒绝异常

两个核心问题导致你无法单独捕获errno13权限错误：

1. 异常捕获顺序错误：PermissionError是OSError（Windows平台中WindowsError是OSError的别名）的子类，如果你把父类异常的except块写在子类前面，子类异常会被父类块提前拦截，永远走不到后面的PermissionError处理分支。
2. 捕获的异常类型不匹配：shutil.copytree复制目录时默认不会直接抛出原始的PermissionError/WindowsError，而是会收集整个复制过程中遇到的所有错误，最终抛出shutil.Error。你看到的包含三元路径元组的输出，就是shutil.Error的标准字符串格式，这个异常本身没有winerror属性，所以你在WindowsError块里判断winerror自然匹配不到errno13的权限错误。

你可以根据需求二选一：

方案1：直接捕获原始权限错误（推荐） #

给shutil.copytree传入错误回调，让它遇到错误时直接抛出原始异常，再按「子类在前、父类在后」的顺序捕获即可：

import shutil
import errno

def throw_original_error(func, path, exc_info):
    # 直接抛出捕获到的原始异常，不做收集
    raise exc_info[1]

try:
    print('Copying files...')
    shutil.copytree(
        'C:/Users/' + userName + '/AppData/Roaming/Test/test1/',
        'C:/Users/' + userName + '/Desktop/test',
        onerror=throw_original_error
    )
    print('Success!')
# 子类异常放最前面，优先匹配
except PermissionError as e:
    if e.errno == errno.EACCES: # errno.EACCES 就是数值13
        print('You do not have the required privileges to make changes to this file.')
        print('One of the following solutions may work:')
        print('   >The file might be open in another location, close the file and try again.')
        print('   >Try to run the program as administrator.')
except WindowsError as e:
    if e.winerror == 2 or e.winerror == 3:
        print('Requested file does not exist.')
    else:
        print('Unexpected Windows exception occurred. Please copy the following exception and send it to test at test@test.com')
        print(e)
        quit()
except Exception as e:
    print('Unexpected exception occured. Please copy the following exception and send it to test at test@test.com')
    print(e)
    quit()

方案2：保留默认错误收集逻辑，解析shutil.Error #

如果你需要保留copytree收集所有错误的特性，可以直接捕获shutil.Error，遍历它携带的错误列表判断是否存在权限错误：

import shutil
import errno

try:
    print('Copying files...')
    shutil.copytree(
        'C:/Users/' + userName + '/AppData/Roaming/Test/test1/',
        'C:/Users/' + userName + '/Desktop/test'
    )
    print('Success!')
except shutil.Error as e:
    # e.args[0] 是所有错误的列表，每个元素格式为(源路径, 目标路径, 异常信息)
    has_permission_denied = False
    for src, dst, err in e.args[0]:
        # 匹配Python3环境下的PermissionError实例
        if isinstance(err, PermissionError) and err.errno == errno.EACCES:
            has_permission_denied = True
            break
        # 兼容Python2环境下错误信息为字符串的情况
        if isinstance(err, str) and 'Errno 13' in err:
            has_permission_denied = True
            break
    if has_permission_denied:
        print('You do not have the required privileges to make changes to this file.')
        print('One of the following solutions may work:')
        print('   >The file might be open in another location, close the file and try again.')
        print('   >Try to run the program as administrator.')
    else:
        print('Unexpected exception occurred. Please copy the following exception and send it to test at test@test.com')
        print(e)
        quit()
except WindowsError as e:
    if e.winerror == 2 or e.winerror == 3:
        print('Requested file does not exist.')
    else:
        print('Unexpected Windows exception occurred. Please copy the following exception and send it to test at test@test.com')
        print(e)
        quit()
except Exception as e:
    print('Unexpected exception occured. Please copy the following exception and send it to test at test@test.com')
    print(e)
    quit()

• 所有异常捕获必须严格遵循子类在前、父类在后的顺序，否则子类异常永远会被上层父类捕获块拦截。
• Windows平台下winerror=5（访问拒绝）本身就属于PermissionError范畴，和errno13是同类型权限错误，不需要单独写分支判断，统一在PermissionError块处理即可。
• 你最初代码里的except WindowsError, e是Python2专属语法，在Python3环境下会直接抛出语法错误，需要改成except WindowsError as e的写法。

内容的提问来源于stack exchange，提问作者Jatinder Brar