# CMU 15-112: Fundamentals of Programming and Computer Science Class Notes: Getting Started

• Part 1 (Tue Lecture)
• Part 2 (Thu Lecture)

Part 1 (Tue Lecture)

1. Logistics and Preliminaries

2. Running Python
Note: Your TA's will be happy to help with any of these steps!
• Install Python 3.7.x from python.org's download page.
• Run IDLE (the default Python text editor / IDE)
• Edit your Python file
• Run your code (F5 in IDLE by default)

3. Hello World in Python
• Command typed into shell
print("Hello World!")

• File edited in IDLE
Download helloWorld.py, edit it in IDLE, and run it.

print("Hello World!") # This is a comment # print "What will this line do?"

5. Basic Console Output
• Basic print function
print("Carpe") print("diem")

• Print on same line
# You can separate multiple values with commas print("Carpe", "diem") # You can also use end="" to stay on the same line print("Carpe ", end="") print("diem")

• Print using f strings
x = 42 y = 99 # Place variable names in {squiggly braces} to print their values, like so: print(f'Did you know that {x} + {y} is {x+y}?')

6. Importing Modules
• Call without importing
print(math.factorial(20)) # we did not first import the math module # Python output: # NameError: name 'math' is not defined

• Call with importing
import math print(math.factorial(20)) # much better...

Part 2 (Thu Lecture)

1. More Logistics and Preliminaries
• Programming vs Computer Science
• Course Objectives / TP Gallery (see sidebar)

2. More Running Python Ways to make IDLE even better:
• Run your code with cmd-b or ctrl-b
• See line numbers (with idlex) (also learn to use pip!)

3. Syntax, Runtime, and Logical Errors
• Syntax Errors (Compile-Time Errors)
print("Uh oh!) # ERROR! missing close-quote # Python output: # SyntaxError: EOL while scanning string literal

• Runtime Errors ("Crash")
print(1/0) # ERROR! Division by zero! # Python output: # ZeroDivisionError: integer division or modulo by zero

• Logical Errors (Compiles and Runs, but is Wrong!)
print("2+2=5") # ERROR! Untrue!!! # Python output: # 2+2=5

4. Basic Console Input
• Input a string
name = input("Enter your name: ") print("Your name is:", name)

• Input a number (error!)
x = input("Enter a number: ") print("One half of", x, "=", x/2) # Error!

• Input a number with int()
x = int(input("Enter a number: ")) print("One half of", x, "=", x/2)