Doing More

Announcements

• New grade report emails went out!
• Adventure Game Project due on Wednesday night
• Practice exam 1 and learning objectives going out today
  • Solutions and Practice exam 2 will go up by midweek
• Optional section this week (can make up a missed section from earlier) for final study materials
• On Wednesday we’ll wrap up a bit early to get a class picture and leave you time to fill out the class evaluation that should have been emailed to you a week or so back, so please show up!
• Polling: rembold-class.ddns.net

Review Question

The code for the main function of Merge Sort looked like below:

def merge_sort(array):
    if len(array) > 1:
        mid = len(array)//2
        a1 = array[:mid]
        a2 = array[mid:]
        merge_sort(a1)
        merge_sort(a2)
        merge(array, a1, a2)
L = [45, 32, 68, 78, 12, 95, 312, 4, 32]
merge_sort(L)

How many times (including line 10) does merge_sort get called before the list is sorted?

Diff Libraries for Diff Uses

Requests

• Responsible for interacting with http webpages

• Generally used to download some information from the web

• Most frequently use the get method to download a URL

  response = requests.get(|||desired url|||)

  • Returns a special request object, with lots of info about the response
  • Can get the decoded text portion by accessing the text attribute

  print(response.text)

Beautiful Soup

• The text returned by requests is generally raw HTML

• You could parse this yourself, but using a parser like BeautifulSoup can greatly streamline things

  • This is especially true if you are needing to do more complicated actions
  • BeautifulSoup is another great example of an abstract data type!

• You pass in HTML and are returned a custom soup object with many useful methods built in

• One of the more common things you’d want to do with the HTML is to find certain elements on the page

  soup.find_all(|||tag name or class or predicate function|||)

  • Returns a list of everything that meets your requirements

Topic Finder

• Let’s write a program to search all the lecture slides on the class webpage for a specific topic
• Will require a few steps:
  1. Download the main Lecture page
  2. Find all the slide links on the page
  3. For each link, download that page
  4. Search that page for signs of the desired topic and print out if found
• If we were going to run a bunch of searches, it would make more sense to download everything once at the start. But we won’t worry about that here.

Topic Finder Code

import requests
from bs4 import BeautifulSoup


def topic_finder():
    def is_lecture_link(tag):
        """ Filters out anchor tags with Lecture in the text. """
        return tag.name == "a" and "Lecture" in tag.text

    def find_lecture_containing(topic):
        """ Returns a list of lectures that contain the desired topic string. """
        lectures = []
        for lecture in lecture_links:
            content = requests.get("https://willamette.edu/" + lecture.get("href")).text
            if topic.lower() in content.lower():
                lectures.append((lecture.text, "https:/" + lecture.get("href")))
        return lectures

    url = "http://willamette.edu/~jjrembold/classes/cs151/slides/"
    response = requests.get(url)
    soup = BeautifulSoup(response.text, features='lxml')
    lecture_links = soup.find_all(is_lecture_link)

    finished = False
    while not finished:
        target = input("\nWhat topic are you looking for? ")
        if target == "":
            finished = True
        else:
            found = find_lecture_containing(target)
            for lecture in reversed(found):
                name, url = lecture
                print(f"{name}: {url}")

if __name__ == '__main__':
    topic_finder()

General Automation

• There are many libraries and API’s you can use with Python to control or automate things
• Sometimes though, nothing exists, and you need something more primitive
• The PyAutoGUI library gives you methods to simulate moving and clicking the mouse and pressing keys on the keyboard
  • Will need to install through either pip or conda
• Important!
  • Should always have an emergency escape if you start automating the mouse and keyboard!
  • PyAutoGUI has a failsafe if you slam the mouse into one of the window corners

Common Methods

PyAutoGUI Art

• Perhaps easiest to demonstrate with a simple drawing program
• Because it is just moving the mouse, should work with any drawing program: Paint, Photoshop, Krita, etc.
• Initially we’d like to draw a rectangular spiral
• Then can add changing colors if time

Rectangular Spiral

import pyautogui as pag

CHANGE = 50

pag.countdown(10)
pag.click()  # Click to make the window active.
distance = 500
while distance > 0:
    pag.drag(distance, 0, duration=0.5)  # Move right.
    distance -= CHANGE
    pag.drag(0, distance, duration=0.5)  # Move down.
    pag.drag(-distance, 0, duration=0.5)  # Move left.
    distance -= CHANGE
    pag.drag(0, -distance, duration=0.5)  # Move up.