L9 HTTP and Patterns€¦ · Lecture 9: HTTP and Patterns Craig Zilles (Computer Science) March 30, 2020 CS 105. Today 1.The Internet •Domain names, IP, HTTP, HTML, CSS, JS 2.Patterns

Lecture 9: HTTP and Patterns

Craig Zilles (Computer Science)

March 30, 2020

https://go.illinois.edu/cs105fa19

CS 105

Today1. The Internet• Domain names, IP, HTTP, HTML, CSS, JS

2. Patterns• E.g., Even/Odd, Count, Sum, Find, Find Best

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The Internet• Is kind of important• I'm hoping you get the big picture (no memorization)

• Hostname -> name lookup -> IP address• Top-level domains

• You can buy your own domain• URL structure: (three parts: scheme, hostname, path)https://illinois.edu/assets/img/navigation/submenu_about.jpg

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The Internet

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192.168.0.101

192.168.0.182.10.251.47

192.168.0.102

192.168.0.104

ISP

INTERNET

172.217.23.174172.217.23.175172.217.23.176172.217.23.177

Your Homecompany.com

ISP = Internet Service Provider

Domain Name Server (DNS)78.46.75.45

HTTP/HTTPS• HyperText Transport Protocol (HTTP)

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HTML5 = HTML, CSS, Javascript• Separation of Concerns• HTML = content, CSS = styling, JS = interactivity

• HTML documents are hierarchical, cause web pages are• Elements have begin/end tags• Elements can be nested in other elements

• CSS consist of:• Selectors that specify which elements • Attribute : value pairs• Like a Python dictionary

• Javascript is a lot like Python but looks pretty different• variables, expressions, functions, conditionals, loops

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Common Idioms / Patterns• There are structures that show up in lots of programs

• Check if even/odd• Visit everything in a collection• Sum • Counter• Finding "best" in collection• Filtering a collection

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Check if something is even/odd

(value % 2) == 0 # returns True if value is even

(value % 2) != 0 # returns True if value is odd(value % 2) == 1 # returns True if value is odd

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Visit everything in a collection

for thing in collection:… thing …

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Computing a sum / total

total = 0 # initialize variable to zero

… # usually in a looptotal += value # accumulate

… total … # do something with the total

Also Average = sum / count10

Counting

counter = 0 # initialize variable to zero

… # usually in a loop and/or conditional counter += 1 # increment

… counter … # do something with the counter

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Compose patterns to solve problems• Write a function that counts the number of even

elements in a list

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Finding best in a collection

current_best = a value you know is worse than best

for thing in collection:if thing is better than current_best:

current_best = thing

return / do something with current_best

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Filtering a collection (pattern)

newlist = []

for thing in collection:if thing meets criteria:

newlist.append(thing)

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