Modules

Objectives

  • Define what a module is
  • Import code from built-in modules
  • Import code from other files
  • Import code from external modules using pip 
  • Describe common module patterns
  • Describe the request/response cycle in HTTP
  • Use the requests module to make requests to web apps

Why Use Modules?

  • Keep Python files small
  • Reuse code across multiple files by importing
  • A module is just a Python file!

Built-in Modules Example

import random

random.choice(["apple", "banana", "cherry", "durian"])
random.shuffle(["apple", "banana", "cherry", "durian"])
import random as omg_so_random

omg_so_random.choice(["apple", "banana", "cherry", "durian"])
omg_so_random.shuffle(["apple", "banana", "cherry", "durian"])
import random as r

r.choice(["apple", "banana", "cherry", "durian"])
r.shuffle(["apple", "banana", "cherry", "durian"])

Importing Parts of a Module

  • The from keyword lets you import parts of a module
  • Handy rule of thumb: only import what you need!
  • If you still want to import everything, you can also use the from MODULE import * pattern

Different Ways to Import

  • import random
  • import random as omg_so_random
  • from random import *
  • from random import choice, shuffle
  • from random import choice as gimme_one, shuffle as mix_up_fruits

All of these work!

Custom Modules

Custom Modules

  • You can import from your own code too
  • The syntax is the same as before
  • import from the name of the Python file
def fn():
    return "do some stuff"

def other_fn():
    return "do some other stuff"

Custom Modules Example

import file1

file1.fn() # 'do some stuff'

file2.fn() # 'do some other stuff'
file1.py
file2.py

YOUR TURN

External Modules

External Modules

  • Built-in modules come with Python
  • External modules are downloaded from the internet
  • You can download external modules using pip 
pip
  • Package management system for Python
  • As of 3.4, comes with Python by default
  • python3 -m pip install NAME_OF_PACKAGE

External Modules Example

  • termcolor - Adds colors to output in a Python shell
  • pyfiglet - Ascii art creator!

ASCII ART EXERCISE

Use the pyfiglet package!

The __name__ Variable 

__name__
  • When run, every Python file has a __name__ variable
  • If the file is the main file being run, its value is "__main__"
  • Otherwise, its value is the file name
import
  1. Tries to find the module (if it fails, it throws an error),
  2. Runs the code inside of the module being imported,
  3. Creates variables in the namespace of the file with the import statement.

Revisited

When you use import, Python...

Ignoring Code on Import

if __name__ == "__main__":
    # this code will only run
    # if the file is the main file!

YOUR TURN

THIS SECTION IS OPTIONAL

THIS SECTION IS OPTIONAL

THIS SECTION IS OPTIONAL

THIS SECTION IS OPTIONAL

THIS SECTION IS OPTIONAL

THIS SECTION IS OPTIONAL

THIS SECTION IS OPTIONAL

HTTP Introduction

HTTP Introduction

  • Describe what happens when you type a URL in the URL bar
  • Describe the request/response cycle
  • Explain what a request or response header is, and give examples
  • Explain the different categories of response codes 
  • Compare GET and POST requests

The Internet

What Happens When...

  1. DNS Lookup
  2. Computer makes a REQUEST to a server
  3. Server processes the REQUEST
  4. Server issues a RESPONSE

Request/Response cycle

DNS Lookup

Like a Phonebook for the Internet!

DNS Server
google.com
172.217.9.142
facebook.com
157.240.2.35
amazon.com
54.239.17.6

Requests and Responses

Client
(e.g. your computer)

Server

172.217.9.142
<!doctype html>
<html lang="en">
  <!-- 
    HTML for google.com 
    will be here! 
  -->
</html>
GET /
200 OK

HTTP Headers

  • Sent with both requests and responses
  • Provide additional information about the request or response

Header Examples

  • Accept - Acceptable content-types for response (e.g. html, json, xml)
  • Cache-Control - Specify caching behavior
  • User-Agent - Information about the software used to make the request
  • Access-Control-Allow-Origin - specify domains that can make requests
  • Allowed - HTTP verbs that are allowed in requests

Response Headers

Request Headers

Response Status Codes

  • 2xx - Success
  • 3xx - Redirect
  • 4xx - Client Error (your fault!)
  • 5xx - Server Error (not your fault!)

HTTP Verbs

GET
POST
  • Useful for retrieving data
  • Data passed in query string
  • Should have no "side-effects"
  • Can be cached
  • Can be bookmarked
  • Useful for writing data
  • Data passed in request body
  • Can have "side-effects"
  • Not cached
  • Can't be bookmarked

APIs

  • API - Application Programming Interface
  • Allows you to get data from another application without needing to understand how the application works
  • Can often send data back in different formats
  • Examples of companies with APIs: GitHub, Spotify, Google

Using the requests Module

requests Module

  • Lets us make HTTP requests from our Python code!
  • Installed using pip
  • Useful for web scraping/crawling, grabbing data from other APIs, etc

Making a Request

import requests

response = requests.get("http://www.example.com")

Request Headers

import requests

response = requests.get(
    "http://www.example.com",
    headers={
        "header1": "value1",
        "header2": "value2"
    }
)

What's a Query String?

  • A way to pass data to the server as part of a GET request
  • http://www.example.com/?key1=value1&key2=value2
  • Browsers enforce a maximum size on length of the query string

Query String

# option 1

import requests

response = requests.get(
    "http://www.example.com?key1=value1&key2=value2"
)
# option 2 - preferable!

import requests

response = requests.get(
    "http://www.example.com",
    params={
        "key1": "value1",
        "key2": "value2"
    }
)

POST Request

import requests
import json

response = requests.post(
    "http://www.example.com",
    data=json.dumps({
        "key1": "value1",
        "key2": "value2"
    })
)

A Note on APIs

  • Some APIs require a key in order for you to use them
  • Especially true of APIs that allow you to send data, rather than just getting data
  • Typically sent as part of URL
  • API keys allow for greater control of how users interact with the API
  • Instructions for obtaining a key vary by API

Recap

  • Python modules let you import code from other files
  • There are three types of modules: built-in, custom, and external
  • pip is the package management system for Python
  • To ignore code during an import, use if __name__ == "__main__"
  • Fundamental Internet vocabulary: DNS, Request/Response, Headers, Status Codes, HTTP Verbs, etc.
  • Requests is a module for making HTTP requests in Python

YOUR TURN

Modules

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Modules

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