Table of Contents

1. Challenge

   Create package.

   To begin, we're going to structure our package with all of our business logic within a src directory. Here's a way we can create our basic structure:

   $ mkdir hr
   $ cd hr
   $ mkdir -p src/hr
   $ touch src/hr/__init__.py
   $ touch README.rst
   

   Next, we'll create a virtualenv for our project using pipenv:

   $ pipenv --python python3.7
   

   Finally, we'll create our setup.py so that we can install our package later.

   Note: Here's the official documentation on how to write a setup script.

   setup.py

   from setuptools import setup, find_packages
   
   with open('README.rst', encoding='UTF-8') as f:
     readme = f.read()
   
   setup(
       name='hr',
       version='1.0.0',
       description='Command line user export utility',
       long_description=readme,
       author='Your Name',
       author_email='[email protected]',
       packages=find_packages('src'),
       package_dir={'': 'src'},
       install_requires=[]
   )
   

2. Challenge

   Implement CLI interface.

   With the package created, we're going to build the application one logical piece at a time. Let's start by building the CLI using argparse and the add_argument method.

   src/hr/cli.py

   import argparse
   
   def create_parser():
       parser = argparse.ArgumentParser()
       parser.add_argument('--path', help='the path to the export file')
       parser.add_argument('--format', default='json', choices=['json', 'csv'], type=str.lower)
       return parser
   

   Now we have a parser that we can use in the main function for our tool.

3. Challenge

   Format user information.

   Before we can export the information about the system's users, we'll need to get the information from the system's password database in a format that we can easily work with. We'll rely on the pwd package to do this. Let's add some functions to handle this in src/hr/users.py:

   src/hr/users.py

   import pwd
   
   def fetch_users():
       users = []
       for user in pwd.getpwall():
           if user.pw_uid >= 1000 and 'home' in user.pw_dir:
               users.append({
                 'name': user.pw_name,
                 'id': user.pw_uid,
                 'home': user.pw_dir,
                 'shell': user.pw_shell,
               })
       return users
   

   This fetch_users function will handle formatting all of the information that we need before we export it.

4. Challenge

   Write JSON and CSV.

   Before wiring everything together, we're going to create a few functions to handle exporting our user information. These will heavily rely on the standard library json and csv packages. Let's add our functions to src/hr/export.py, starting with exporting JSON:

   src/hr/export.py

   import json
   
   def to_json_file(export_file, users):
       json.dump(users, export_file, indent=4)
       export_file.close()
   

   This function basically just wraps the built in json.dump function while also closing the file.

   The CSV export will be a little more complicated:

   src/hr/export.py

   import csv
   import json
   
   def to_json_file(export_file, users):
       json.dump(users, export_file, indent=4)
       export_file.close()
   
   def to_csv_file(export_file, users):
       export_file.write('name,id,home,shell\n')
       writer = csv.writer(export_file)
       rows = [[user['name'], user['id'], user['home'], user['shell']] for user in users]
       writer.writerows(rows)
       export_file.close()
   

5. Challenge

   Wire the pieces together.

   With all of the individual parts ready, it's time to put them all together. Let's create a main function as part of our hr/src/cli.py file:

   src/hr/cli.py

   import argparse
   
   def create_parser():
       parser = argparse.ArgumentParser()
       parser.add_argument('--path', help='the path to the export file')
       parser.add_argument('--format', default='json', choices=['json', 'csv'], type=str.lower)
       return parser
   
   def main():
       import sys
       from hr import export, users
       from hr import users as u
   
       args = create_parser().parse_args()
       users = u.fetch_users()
   
       if args.path:
           file = open(args.path, 'w', newline='')
       else:
           file = sys.stdout
   
       if args.format == 'json':
           export.to_json_file(file, users)
       else:
           export.to_csv_file(file, users)
   

   Now that we have a function to run, we need to add it as one of the console_scripts in our setup.py:

   setup.py

   from setuptools import setup, find_packages
   
   with open('README.rst', encoding='UTF-8') as f:
     readme = f.read()
   
   setup(
       name='hr',
       version='1.0.0',
       description='Command line user export utility',
       long_description=readme,
       author='Your Name',
       author_email='[email protected]',
       packages=find_packages('src'),
       package_dir={'': 'src'},
       install_requires=[],
       entry_points={
           'console_scripts': 'hr=hr.cli:main',
       },
   )
   

6. Challenge

   Install the `hr` tool.

   With everything built and wired together, we're ready to install the tool so that our user can access it:

   $ pip3.7 install --user -e .
   Obtaining file:///home/cloud_user/hr
   Installing collected packages: hr
     Running setup.py develop for hr
   Successfully installed hr
   $ hr --help
   usage: hr [-h] [--path PATH] [--format {json,csv}]
   
   optional arguments:
     -h, --help           show this help message and exit
     --path PATH          the path to the export file
     --format {json,csv}