Python Intro

Original Presentation by Grace (last year’s VP)

Adapted a bit by Elliott

• Cuz they don’t teach you python anymore…

What is Python?

• Coding language
• One of the easiest for beginners to learn
• Very basic syntax
• Best way to learn is by using it
• Super widespread
• Common to see in CTF challenges
• Useful for solving a lot of CTF challenges

How do I install Python?

If you have a school Chromebook:

• Open Ion
• Open OnDemand
• Pick an editor
• Create a new Python file

Or, switch to a Dell/bring a personal computer!

• If you’re taking a CS class this year, you should do this anyway

Alternative solutions: use an online Python compiler

Otherwise:

• https://www.python.org/downloads/
• Popular code editors:
• Visual Studio Code (what I use)
• JGrasp (CS class editor)
• PyCharm
• IDLE (default editor)
• Jupyter Notebook (also what I use)

The basics

Using Python, variables, math, logic, loops, functions, and data structures

Using Python

← input

← output

On the terminal:

Running files:

Result:

Variables

• Labels for storing data
• Different types:
• String
• Integer
• Float (decimal number)
• Boolean (true/false)
• Etc.

​

Math

• Kind of self-explanatory

+ ← addition

- ← subtraction

* ← multiplication

/ ← division

// ← integer division (truncates decimal place)

% ← modulo (remainder)

** ← exponent

• Can also be performed on strings

Conditionals

• If, elif, else
• Evaluates an expression to a boolean
• Uses colons afterward

Loops

Two types of loops: for-loops and while-loops

For loops:

• Iterate over an iterable (range object, string, list, etc.)

​

While loops:

• Continues until the condition is no longer satisfied

Functions

• Reusable blocks of code
• Take parameters (input) and can return something

Data Structures

There are 4 main types of built-in Python data structures: lists (arrays), dictionaries, tuples, and sets.

← Arrays use [ ]

← Dictionaries use { }

← Tuples use ( )

← Sets also use { }

Data Structures: Lists

• A 1D array that can store multiple data types
• Ordered by insertion
• Elements can be accessed by index; indices begin at 0
• Mutable (aka can be changed after creation)

What is slicing?

• Allows you to extract pieces of a list
• [ start : stop : step ]
• stop is not inclusive
• Makes another array

Data Structures: Dictionaries

• Key-value pairs
• Keys must be of a hashable, mutable data type (strings, numbers, tuples, etc.) and must be unique!
• Stay in insertion order (Python 3.7+)
• Retrieve values using keys
• e.g. myDict[key1] returns the value that corresponds to key1
• Can contain multiple data types

Data Structures: Tuples & Sets

Tuples:

• Immutable, hashable arrays
• Also indexed
• Allow duplicates
• Can’t be changed once they’re created

Sets:

• Cross between an array and a dictionary
• Mutable (can change after creation)
• Don’t allow duplicates
• Use hashing for order (not in order of insertion)

Libraries

• Collections of pre-written code
• Include modules, functions, etc.
• Examples: NumPy, pandas, matplotlib, scikit-learn, Flask, tensorflow, etc.
• Typically installed with pip and imported into Python scripts

​

​

​

Some last useful commands

• Chr(int) returns ASCII character

​

• Ord(character) returns ASCII number

​

• String.encode/decode – conversions to and from byte strings

Resources

Do your own research!

https://www.w3schools.com/python/python_intro.asp ← Python intro

https://codingbat.com/python ←excellent beginner Python practice

https://www.programiz.com/python-programming/online-compiler/ ← online Python compiler

https://docs.pwntools.com/en/stable/install.html ←pwntools, a CTF framework and exploit development library

Go solve challenges!