Question

所以我用Python编写一个shell，文件名为jsh.py。当我运行代码时，由于某种原因它不起作用。弹出一个窗口但立即关闭。什么是我的代码？

import os
import random
import time
import path
import string
import sys

commandAvail = 'ls where chdir mk mkdir cp mv rm rmdir view ext shutdown edit unix dos man-all man-unix man-dos'
commandAvailUnix = 'exec permission group'
commandAvailDos = ' '
print('Welcome to jsh alpha 1!')
commandPlatform = input('System: (UNIX/DOS):')
commandLine()

def commandLine():
        while 1 == 1:
                command = input('$ ')
                if command in commandAvail:
                        if command.startswith('ls'):
                                commandKeyword = 'ls'
                                commandOptions = command - commandKeyword
                                ls(commandOptions)
                        elif command.startswith('where'):
                                commandKeyword = 'where'
                                commandOptions = command - commandKeyword
                                where()
                        elif command.startswith('chdir'):
                                commandKeyword = 'chdir'
                                commandOptions = command - commandKeyword
                                chdir()
                        elif command.startswith('mk'):
                                commandKeyword = 'mk'
                                commandOptions = command - commandKeyword
                                mk()
                        elif command.startswith('mkdir'):
                                commandKeyword = 'mkdir'
                                commandOptions = command - commandKeyword
                                mkdir()
                        elif command.startswith('cp'):
                                commandKeyword = 'cp'
                                commandOptions = command - commandKeyword
                                cp()
                        elif command.startswith('mv'):
                                commandKeyword = 'mv'
                                commandOptions = command - commandKeyword
                                mv()
                        elif command.startswith('rm'):
                                commandKeyword = 'rm'
                                commandOptions = command - commandKeyword
                                rm()
                        elif command.startswith('rmdir'):
                                commandKeyword = 'rmdir'
                                commandOptions = command - commandKeyword
                                rm()
                        elif command.startswith('view'):
                                commandKeyword = 'view'
                                commandOptions = command - commandKeyword
                                rm()
                        elif command.startswith('edit'):
                                commandKeyword = 'edit'
                                commandOptions = command - commandKeyword
                                edit()
                        elif command == 'man-all':
                                print('Commands that work for all underlying platforms:')
                                print(commandAvail)
                        elif command == 'man-unix':
                                print('Commands that only work on Unix systems:')
                                print(commandAvailUnix)
                        elif command == 'man-dos'
                                print('Commands that only work on DOS systems:')
                                print(commandAvailDos)
                        elif command.startswith('unix'):
                                commandType = 'unix'
                                unix()
                        elif command.startswith('dos'):
                                commandType = 'dos'
                                dos()
                        elif command.startswith('ext'):
                                commandKeyword = 'ext'
                                commandOptions = command - commandKeyword
                                ext()
                        elif command == 'shutdown':
                                sys.quit(0)
                        else:
                                print('jsh has experienced an internal error and has to shutdown.')
                                sys.quit(10)
                else:
                        print('Command \'' + command + '\' not recognized as internal or external.')

def ls(options):
        if commandPlatform == 'UNIX':
                os.system('ls' + options)
        else:
                os.system('dir' + options)
        commandLine()

Answer 1

你忘了在elif命令=='man-dos'之后加上'：'

运行：python3 yourscript用于调试目的。

Answer 2

您当前的代码中存在多个错误：

首先，你有一些混乱的缩进，包括用于缩进的标签和空格的混合。这在Python中非常糟糕，因为不正确的缩进是语法错误。我已经修正了问题中的代码以正确显示（每个标签使用8个空格），但您也需要在文件中修复它。另外，请注意Python约定是每个块缩进四个空格，因此您可能希望将编辑器设置为默认情况下执行此操作。
其次，您的顶级检查逻辑不正确。您正在测试整个命令字符串是否包含在commandAvail变量中的命令字符串中。如果命令除了命令名之外还有参数，那么这将是错误的。我建议您split命令字符串获取术语列表，然后仅根据可用命令测试第一个术语。而不是进行子字符串搜索，我建议将commandAvail拆分为一组字符串：
```
# make a set of commands that we recognize
commandAvail = set('ls where chdir mk mkdir cp'.split()) # trimmed for space

# then later, test against it
command = input().split()
if command[0] in commandAvail: # this is much more efficient!
    # do stuff
```
最后，您尝试从命令字符串中删除命令本身的方式是错误的。你不能从另一个字符串中减去一个字符串（如果你尝试，你会得到一个TypeError）。幸运的是，我为上一期提出的解决方案在这方面会有所帮助。由于split调用，您将拥有一个术语列表，而不是进行字符串操作。现在，您只需测试第一项（命令），并将其余项作为参数传递。

事实上，这表明实现比您目前拥有的if / elif块的大链更简单。使用字典在命令字符串和实现它们的函数之间进行映射：
```
# map command names to the functions that implement them
command_dict = {"ls":ls, "where":where, "chdir":chdir} # snipped

# the main loop
while True:
    # command is first term, the rest go into args
    command, *args = input().split()

    try: # use "easier to ask forgiveness than permission" idiom
        command_dict[command](*args) # call function from command_dict
    except KeyError:
        print("Unknown command: {}".format(command))
```

奇怪的Python 3错误

2 个答案: