Resources from lecture

• Link to all code written in lecture

Intro to Course Logistics

• Review the syllabus at this link: https://ucsb-cs8.github.io/w19-mirza//info/syllabus/

Learning Something New

• Basketball: drills vs. playing the game
• Swimming, Painting, Guitar

Intro to the Unix environment

• Unix file system
• Navigating the file system using Command Line
• Learn a few unix commands: ls, pwd, mkdir, cd, cp, mv

Getting started with Python and IDLE

• Python REPL (Read Eval Print Loop)

Also called the Python Shell Prompt

Python 3.4.3 (default, Aug  9 2016, 15:36:17)
[GCC 5.3.1 20160406 (Red Hat 5.3.1-6)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 2 + 3
5
>>> 2 + 7 *4
30
>>> 2 ** 3
8
>>> 2 ** 3 ** 2
512
>>> 2 * 3 * 4
24
>>> (2 * 3) * 4
24
>>> 2 * (3 * 4)
24
>>> (2 ** 3) ** 2
64
>>> 2 ** (3 ** 2)
512
>>>

Note that ** is right associative, not left associative.

• Writing simple programs in the editor

  Python as a calculator

• Numerical data types
  • Integer representing non-decimal values
  • float: Floating point number representing a decimal (fractional) value
• Operations with numeric types
  • Arithmetic (+ - * /), Comparison(== < > <= >=)
• Evaluating expressions:
  • Just like writing math expressions
  • Mixed types are okay

Numerical type examples (type these in the shell to see what happens)

>>> 1

>>> 1+2

>>> 4/2

>>> 1/3

>>> 6/2

>>> 1/0

>>> 1+2*4

Storing data using variables

• Think of a variable as a box with a name
• Just like you can store things in a box, you can store values in a variable (for now we’ll only store numeric values, but you can store other types as well)
• Names of variables must…
  • Start with a letter or underscore (the former is more common)
  • Remaining letters in variables names can consist of letters, numbers, or underscores
  • Names are case-sensitive (name and NAME are considered two different variables).

>>>x = 10 #What is the value of x?

>>>x = x * 10 # 10 * current value of x is stored back into x

More than just a calculator

• Other data types
  • int: Integer representing non-decimal values
  • float: Floating point number representing a decimal (fractional) value.
  • string: Represents a collection of characters
    • Examples of characters: ‘A’, ‘a’, ‘1’, ‘ ‘, …
  • bool: Evaluates to either True or False
    • Ex: 4 <= 6 True
    • Ex: 1 == 2 False
  • Note: 3 and 3.0 are considered different types
    • 3 is an integer
    • 3.0 is a float
  • Python knows what type these numbers are based on its value.
• Numerical type examples

x = 1
print(x)
print(type(x))

x = 4 / 2
print(x)
print(type(x))

y = 4 * 2
print(y)
print(type(y))

z = 4 * 2.0
print(z)
print(type(z))

x = "CS 8"
print(x)
print(x*2)

x = "8.0" # string not float
print(x) #8.0
print(type(x)) #str

print(x + 2) #ERROR
print(x + "2") # No error, uses concatenation

print(float(x) + 2) # No error, 10.0

x = "8.0" # Be careful ...
print(int(x)) #crashes

x = "8"
print(int(x))

x = "8.0"
y = "8.0"
z = "8.00"

print(x == y) #True
print(x == z) #False
print(float(x) == float(z)) #True
print(2 * 3 > 5) #True
print(type(2 * 3 > 5)) # bool

Interacting with a program using print and input

• When we write software, we’re modeling the real world
  • … or at least we do it as best we can
  • You can think of everything with respect to things and actions.
    • Things (nouns) - Objects
    • Actions (verbs) - Functions, operators, …
  • Python (and generally all languages) gives some way to represent and combine these.
  • There are also ways to interact with the program
    • Generally, we call this “user input”
    • Reading files
    • clicking on buttons
    • keyboard characters
  • In order to interact with our program using text, Python has the input() function for us to use

```python

Example

print(“Hi, please enter your name: “) userName = input() print(“Hello”, userName)