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

• Part 1 (Tue Lecture)
  1. Logistics and Preliminaries
  2. Running Python
  3. Hello World in Python
  4. Python Comments
  5. Basic Console Output
  6. Importing Modules
• Part 2 (Thu Lecture)
  7. More Logistics and Preliminaries
  8. More Running Python
  9. Syntax, Runtime, and Logical Errors
  10. Basic Console Input

1. Logistics and Preliminaries
   • Course web site (http://www.cs.cmu.edu/~112)
   • Course Policies / Syllabus
   • Course Schedule
   • Waitlist policy
   • 15-112 vs 15-110


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.


4. Python Comments
   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...

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


8. 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!)


9. 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


10. 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)