You've seen this book 2000 words of admonition, for those who want to learn Python, I suggest you look after your collection! Should all readers of the book be a little impressed by a command?Yes, it is the ls command that is often used in linux.

I mentioned how to improve my python capabilities in this article?Find projects to write directly, but as a zero-base/whitespace/starter, blogging with web frameworks, html, css, js is another obstacle that prevents you from writing actual projects.

So I recommend this command: ls.Writing an LS is very simple. You just need a little bit of linux basics to know what LS can do.

So today I'll give you a code on how to use ls.py. That's right. windows is OK.

Demonstration environment

• Operating system: windows10
• python version: python 3.7
• idea: pycharm 2018.2
• Use module: argparse, os

Understanding the argparse module

argparse is python's standard library, which allows us to write a command-line interface friendly, generate help documents and usage messages automatically, and issue errors when parameters are invalid.

Understanding argparse.ArgumentParse class parameters

1. Prog: To change the name of the application, we can use%(prog)s to reference the name of the application. The default application name is the file name.
2. Usage: Displays this command usage, typically used to display parameters
3. description: Displays help information for this command
4. epilog: Displays help information for the command, located below the parameters

Understanding the argparse.ArgumentParser.add_argument function

1. name | flags: Name of the specified parameter
2. action: Specifies command line parameters, built-in as follows
   • store: Default value, only parameter values are saved.
   • store_const: Almost identical to store, but only the value specified by the const keyword will be saved, other values will fail
   • store_true | store_false: Much like store_const, only True and False are saved
   • append: Save different values of the same parameter in a list
   • count: Number of occurrences of statistical parameters
   • Help:Output program help information
   • Version: Output program version information
3. nargs: Associate a different number of values with a parameter
   • nargs=N:N is an integer
   • nargs='?'
   • nargs='*': Save all parameters in the list
   • nargs='+': Save all parameters in the list, but at least one parameter is required
   • nargs=argparse.REMAINDER: All remaining parameters are saved in a list
4. Default: If this parameter is not passed in, the default parameter value is used by default
5. type: The received parameter is processed by the function corresponding to this parameter.
6. choices: Specify parameters in a range, error if exceeded
7. Required: Specifies whether the parameter is required.
8. dest: Name of the custom parameter, default name is'-followed by value'or'--followed by value'.

Scripting ls commands

Here we simply specify three parameters.

• -a: Add-a parameter to show hidden files.
• -r: Add the-r parameter to recursively display the files under the folder.
• -d: Specifies the display directory, if not, defaults to the current directory.

First, we use the ArgumentParser class to specify parameters.

import os
import argparse

parser = argparse.ArgumentParser(prog='ls', description='Show files under folders')

# Specify parameters
parser.add_argument('-a', '--all', const=True, nargs='?', help='Whether to show hidden files')
parser.add_argument('-d', '--directory', help='Specifies the directory to display, if not specified, defaults to the current directory')
parser.add_argument('-r', '--recursion', const=True, nargs='?', help='Whether to show recursively')

# Parsing parameters
args = parser.parse_args()

# Get the directory parameter, if it's not passed, it's None
directory = args.directory
# If directory has value
if directory:
    # Throw an exception if the specified directory does not exist
    if not os.path.exists(directory):
        raise ValueError(f'{directory} does`t exist')

    # Throw an exception if directory is not a directory
    if not os.path.isdir(directory):
        raise ValueError(f'{directory} is not a directory')

# Assign a value to directory if directory is None
else:
    directory = '.'

Once we have defined the parameters, the next step is to implement the specific ls.We encapsulate an LsCommand class

class LsCommand():
    def __init__(self, show_all=False, directory='.', recursion=False):
        '''
        :param show_all: Whether to show hidden files
        :param directory: Specified File Directory
        :param recursion: Whether to display files in directories recursively
        '''
        self.show_all = show_all
        self.recursion = recursion
        self.directory = os.path.abspath(directory)


    def handle_dir(self, directory, grade=1, placeholder='--'):
        '''
        //Processing Directory
        :param directory: File directory
        :param grade: Catalog hierarchy
        :param placeholder: Placeholder before subdirectory file
        :return:
        '''
        # Determine whether it is a folder

        # Has grade increased

        # os.listdir: List all files and folders under the current folder
        # Traverse files, folders under directories
        pass

    def show_file_or_dir(self, file, prefix=''):
        # If hidden files are not displayed

        # Print prefix and file name
        pass

    def run(self):
        '''
        //Run ls command
        :return:
        '''
        # os.listdir(dir) gets all the files, folders in the dir directory

        # Traverse the self.directory directory first all files, folders

        pass

The ls class is also encapsulated. Next we pass the parameters into the LsCommand class and run them to get a pleasant result.

ls = LsCommand(bool(args.all), directory, bool(args.recursion))
ls.run()

Effect display:

python ls.py

python ls.py -a

python ls.py -a -r

python ls.py -d ./temp

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