COMP1701-004

fall 2023

lec-04

Off In the Distance

any A1 Part 3 questions?

I have a few comments about the first parts.

Learning moment for both parties!

speaking of questions

This might be a good keyboard shortcut to memorize.

hamburger

btw: hot dog

continuing to speak of questions

onlinequestions.org

202304170104

RECALL

Did you know?...

let's talk about these  things today:

⦾ variables

⦾ data types

⦾ operators

variables

Section 2.7 in our text.

weight

blood_type

  • computer memory is a bunch of "little boxes" next to each other

  • each box holds ONE thing

  • each box can be given a "name"

  • each box/label combo is a variable

One way of viewing a variable:
as a little box with a name.

34

"A"

variables

Memory only holds 0's and 1's....

...but that's only a useful detail in advanced situations, so we handwave it most of the time.

But you still have to remember this -
it will definitely resurface in future courses!

weight

blood_type

00100010

01000001

This just in:

variables

assigning values to variables 

weight = 34

What's blah = blahblah called again?!?

Which of our 7 measly things are these?

weight

blood_type

34

"A"

   
blood_type = "A"

variables

syntax for Python variables

syntax: rules for combining symbols resulting in valid code for a given language

  1. start with a letter or _
  2. contain only letters, numbers, _

Just 2 Rules: variable names MUST

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variables

naming conventions for Python variables

naming conventions: guidelines for the format of names used in a specific language

  1. ...contain only lowercase letters
  2. ...separate words with _ (aka "snake_case")

Just 2 Conventions: variable names SHOULD...

PEP 8

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variables

best practices for naming variables

best practices: practices to follow if you want to be considered a "good developer"

  1. ...expressive - they should never confuse or deceive
  2. ...concise - but if this conflicts with 1, 1 should win

Just 2 Practices: variable names SHOULD BE...

*

A very important truth:

“Programs are meant to be read by humans and only incidentally for computers to execute.”

- Donald Knuth

Follow the syntax to make the computer happy. Follow conventions and best practices to make your fellow programmers happy.

- JP

Which leads to this advice:

variables

check your noggin

x

1potato

num_lotions_in_basket

gravForceOnMoon

_coins_in_hand

Life_Remaining

_

print

temp_1

Which of these...

  • are syntactically correct?
  • follow Python naming conventions?
  • follow best practices?

== FRIENDLY WARNING ==
You don't have the squiggles on a written test.

data types

Do you think 14 and 14.000 are the same things?

How about 42 and "42"?

data types

Type Represents Examples
int integer numbers 12, 0, -15918291
float floating-point numbers 3.14, -1.0
str a string of characters (text) 'yo', "", "game over, man", '2', '4/6'
bool Boolean values True, False

common data types in Python

empty string

very common term

data types

variables in Python are dynamically typed 

somevar = 5
somevar = -3000.1234
somevar = "There's a snake in my boot!"
somevar = True

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data types

Python is strongly typed 

4 + 6  # ok

4 + 6.0 # also ok...but interesting...

6 / 2 # saywhatnow?

5 + "howzitgoing?" # nope

"True" + True

True + "True"

true + "false" # careful!

Would you REPL this to find out? Or script it?

Are you predicting as we go through these? You really, really should.

Are you reading the errors coming up and trying to understand 'em?

data types

variables in Python are also strongly typed 

num_my_cats = 0
num_your_cats = 4
curr_volume = 11.0
fav_movie = "Aliens"
everything_is_groovy = True

num_my_cats + num_your_cats

curr_volume * num_my_cats

fav_movie * num_your_cats

everything_is_groovy - num_my_cats

Are you predicting as we go through these? You really, really should.

Are you reading the errors coming up and trying to understand 'em?

If there are no errors and you thought there would be, what's going on?

data types

Python allows explicit type casting 

float(4) + 6 

4 + int(6.0)

str(5) + "howzitgoing?" 

"True" + str(True)

Are you still predicting?!?! Or has your brain turned to goo?

Mini Brain Break!

operators

Wait...what's an "operator"?!?

Ah - sorry. It's just a symbol (or sometimes a word, as we'll see in a few weeks) that means "do something with the two thingies on either side of the operator".

Cleared that right up, yes?

operators

2 + 3
pallets = 4
x = 12 // num_bags

the assignment operator 

num_chickens = 17

Which of our 7 measly things does this show?

What did we call this kind of statement?

the math operators

Math operators (like + - / * ) are fairly self-explanatory, but you have to be a bit careful, because familiar multiplication and division shorthands aren't available.

3(x + 2)
(x + y)

4

3 * (x + 2)
(x + y) / 4

**    (the exponent operator)

There are also some weirdos we should talk about:

%      (the modulus operator)

//      (the floor division operator)

aka integer division

math operators

the
exponent operator 

x = 3**2

math operators

the
modulus operator

Find what's "left over" after doing integer division.

num_eggs = 17
leftover = num_eggs % 12

print("There are", leftover, "eggs left over.")

math operators

the
floor division operator

Rounds down to the nearest integer.

num_eggs = 17
num_cartons = num_eggs // 12

print("You need", num_cartons, "to hold", num_eggs, "eggs.")

Which of our 7 measly things do you see happening here?

math operators

a brief word about
parenthesis

use them

Data types and operators go hand in hand...how the operators "behave" depends on the data types involved!

This is an important abstract concept, but I didn't know how to bring it in earlier, so I have this awkward slide here.

RECAP

What did we talk about today?

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