Class 4B: Introduction to Programming in Python¶

We will begin at 2:00 PM! Until then, feel free to use the chat to socialize, and enjoy the music!

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September 29, 2021
Firas Moosvi

Class Outline:¶

Digging Deeper into Python syntax
- Announcements (5 min)
  - Thursday labs will be cancelled this week (Nat’l day of truth and reconciliation)
  - Project 1 Milestone Feedback has now been released
  - Project Details are also released
  - Test details
    - Test 1 will be from Friday 6 PM - Sunday 6 PM (48 hour window)
    - You can start the test at any time during this window
    - You will have 1 hour to do the test (Canvas Quiz)
    - Content: Terminal & Git commands & Markdown syntax
- Basic datatypes (15 min)
- Lists and tuples (15 min)
- String methods (5 min)
- Dictionaries (10 min)
- Conditionals (10 min)

Basic datatypes¶

A value is a piece of data that a computer program works with such as a number or text.
There are different types of values: 42 is an integer and "Hello!" is a string.
A variable is a name that refers to a value.
- In mathematics and statistics, we usually use variables names like \(x\) and \(y\).
- In Python, we can use any word as a variable name (as long as it starts with a letter and is not a reserved word in Python such as for, while, class, lambda, import, if, else, etc.).
And we use the assignment operator = to assign a value to a variable.

See the Python 3 documentation for a summary of the standard built-in Python datatypes. See Think Python (Chapter 2) for a discussion of variables, expressions and statements in Python.

Common built-in Python data types¶

English name	Type name	Description	Example
integer	`int`	positive/negative whole numbers	`42`, `-42`, `-10000`
floating point number	`float`	real number in decimal form	`3.14159`
boolean	`bool`	true or false	`True`
string	`str`	text	`"I Can Has Cheezburger?"`
list	`list`	a collection of objects - mutable & ordered	`["Ali","Xinyi","Miriam"]`
tuple	`tuple`	a collection of objects - immutable & ordered	`("Thursday",6,9,2018)`
dictionary	`dict`	mapping of key-value pairs	`{'name':'DSCI','code':511,'credits':2}`
none	`NoneType`	represents no value	`None`

Numeric Types¶

x = 45
print(x)

type(x)

int

print(x)

x # in Jupyter we don't need to explicitly print for the last line of a cell

pi = 3.14159

print(pi)

3.14159

type(pi)

float

Arithmetic Operators¶

The syntax for the arithmetic operators are:

Operator	Description
`+`	addition
`-`	subtraction
`*`	multiplication
`/`	division
`**`	exponentiation
`//`	integer division
`%`	modulo

Let’s apply these operators to numeric types and observe the results.

1 + 2 + 3 + 4 + 5

0.1 + 0.2

0.30000000000000004

Tip

Note From Firas: This is floating point arithmetic. For an explanation of what’s going on, see this tutorial.

2 * 3.14159

6.28318

2**10

type(2**10)

int

2.0**10

1024.0

int_2 = 2

float_2 = 2.0

float_2_again = 2.

101 / 2

50.5

101 // 2 # "integer division" - always rounds down

101 % 2 # "101 mod 2", or the remainder when 101 is divided by 2

None¶

NoneType is its own type in Python.
It only has one possible value, None

x = None

print(x)

None

type(x)

NoneType

You may have seen similar things in other languages, like null in Java, etc.

Strings¶

Text is stored as a datatype called a string.
We think of a string as a sequence of characters.
We write strings as characters enclosed with either:
- single quotes, e.g., 'Hello'
- double quotes, e.g., "Goodbye"
- triple single quotes, e.g., '''Yesterday'''
- triple double quotes, e.g., """Tomorrow"""

my_name = "Firas Moosvi"

print(my_name)

Firas Moosvi

type(my_name)

str

course = "DATA 301"

print(my_name,course)

Firas Moosvi DATA 301

print(my_name+" --------------> "+course)

Firas Moosvi --------------> DATA 301

type(course)

str

If the string contains a quotation or apostrophe, we can use double quotes or triple quotes to define the string.

"It's a rainy day cars'."

"It's a rainy day cars'."

sentence = "It's a rainy day."

print(sentence)

It's a rainy day.

type(sentence)

str

saying = '''They say:

"It's a rainy day!"'''

print(saying)

They say:

"It's a rainy day!"

Boolean¶

The Boolean (bool) type has two values: True and False.

the_truth = True

print(the_truth)

True

type(the_truth)

bool

lies = False

print(lies)

False

type(lies)

bool

Comparison Operators¶

Compare objects using comparison operators. The result is a Boolean value.

Operator	Description
`x == y`	is `x` equal to `y`?
`x != y`	is `x` not equal to `y`?
`x > y`	is `x` greater than `y`?
`x >= y`	is `x` greater than or equal to `y`?
`x < y`	is `x` less than `y`?
`x <= y`	is `x` less than or equal to `y`?
`x is y`	is `x` the same object as `y`?

2 < 3

True

"Data Science" != "Deep Learning"

True

2 == "2"

False

2 == 2.00000000000000005

True

Operators on Boolean values.

Operator	Description
`x and y`	are `x` and `y` both true?
`x or y`	is at least one of `x` or `y` true?
`not x`	is `x` false?

True and True

True

True and False

False

False or False

False

# True                     and True
("Python 2" != "Python 3") and (2 <= 3)

True

not True

False

not not not not True

True

Casting¶

Sometimes (but rarely) we need to explicitly cast a value from one type to another.
Python tries to do something reasonable, or throws an error if it has no ideas.

x = int(5.0)
x

type(x)

int

x = str(5.0)
x

'5.0'

type(x)

str

str(5.0) == 5.0

False

int(5.3)

DATA 301

Class 4B: Introduction to Programming in Python

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