The Standard Library

The Python standard library has a huge number of packages - no matter what you want to do, there’s probably a package included. Let’s practice using some of the more common ones. Create a new file and use the os module to see if you can get a file listing for the folder your new file is in.

import os

my_folder = os.getcwd()
print(f"Here are the files in {my_folder}:")

with os.scandir(my_folder) as folder:
    for entry in folder:
        print(f" - {}")
Here's what you should have seen on your command line:

sys is another commonly useful library, giving you access to some variables and functions used or maintained by the Python interpreter. Let’s try using sys to get the arguments passed into our program from the command line, and to figure out what kind of computer we’re using:

import sys

arguments = sys.argv
print(f"We received the following arguments:")

for arg in arguments:
    print(f" - {arg}")

print(f"We are running on a '{sys.platform}' machine")
Here's what you should have seen on your command line:


PyPI (the Python Package Index) is an awesome service that helps you find and install almost any 3rd party Python package. You can browse the site at but most of the time you will probably interact with it through Python’s pip command line tool.

For example, earlier you may have installed the requests module. If you search pip for requests, you’ll see every package in the index containing the word requests:

(env) $ python -m pip search requests
requests-hawk (1.0.0)                  - requests-hawk
requests-dump (0.1.3)                  - `requests-dump` provides hook functions for requests.
requests-aws4auth (0.9)                - AWS4 authentication for Requests

We just want the one named requests, so we’ll install it with the install keyword. If you don’t have it installed, pip will install it for you. If you installed it earlier, you’ll see something like this:

(env) $ python -m pip install requests
Requirement already satisfied: requests in /usr/local/lib/python3.7/site-packages (2.21.0)
Requirement already satisfied: chardet<3.1.0,>=3.0.2 in /usr/local/lib/python3.7/site-packages (from requests) (3.0.4)
Requirement already satisfied: certifi>=2017.4.17 in /usr/local/lib/python3.7/site-packages (from requests) (2019.3.9)
Requirement already satisfied: idna<2.9,>=2.5 in /usr/local/lib/python3.7/site-packages (from requests) (2.8)
Requirement already satisfied: urllib3<1.25,>=1.21.1 in /usr/local/lib/python3.7/site-packages (from requests) (1.24.1)