from datascience import *
import numpy as np

%matplotlib inline
import matplotlib.pyplot as plots
plots.style.use('fivethirtyeight')

New material¶

Python fundamentals¶

Python as a calculator:

2 + 9

2 * 4

# The line below errors
# * 4

2 ** 4

# The line below errors 
# 2 * * 4

2/9

Python understands the order of operations!

2 + 3 * 9

(2 + 3) * 9

-1 - 1 + 2 * (3 * 4 * 5 / 6) ** 3 + 7 + 8 + 12

Floating point vs integer representation

64 / 8

Strings!

'hello'

'Data 8'

"hello"

'I don't ever want to miss class'

"I don't ever want to miss class"

Names¶

a = 2

Names must first be assgined to a value! The line below causes a name error since b isn’t assigned yet.

b = 3

Discussion Question 1: What will the value of a be once the code in the following cell has finished running?

a = 2 
a + 5

a = a + 5
a

a * b

Discussion Question 2: What will the value of total be once the code in the following cell has finished running?

total = a + b
total

a = 10
total

total

total = a + b
total

The line below causes a syntax error.

a + b = total

Why Names?¶

A cell with arithmetic but no names is difficult to interpret.

Example: On January 1, 2025, the CA Minimum Wage for Employers with 26 Employees or More increased to $16.50/hour. Calculate the yearly minimum wage of an employee who works for such an employer.

Method 1:

40 * 16.5

40 * 52 * 16.5

Method 2:

ca_hourly_minimum_wage = 16.50
hours_per_week = 40
weeks_per_year = 52

weekly_wages = hours_per_week * ca_hourly_minimum_wage
weekly_wages

yearly_wages = weekly_wages * weeks_per_year
yearly_wages

Call Expressions and Arguments¶

abs(-5)

abs(1 - 3)

Names can help us with inputs (called arguments in computer science jargon) to functions!

day_temp = 52
night_temp = 47
abs(night_temp - day_temp)

Functions can take multiple arguments.

min(14, 15)

Some functions can be called with a single argument or with multiple arguments!

round(123.456)

round(123.456, 1)

STOP

round(123.456, ndigits=1)

In the third line, ndigits is a named argument.

How did I know that ndigits would work as a name? You can use ? to figure out everything you want to know about a function.

round?

round(number=123.456)

The line below causes a type error because the wrong name was used.

round(123.456, digs=1)

Tables¶

Example: Ice cream¶

cones = Table.read_table('cones.csv')
cones

cones.show(3)

cones.show()

Table Operations

cones.select('Flavor')

cones.select('Flavor', 'Price')

The line below causes an error because Flavor is not a name, but rather, a column in the cones table.

cones.select(Flavor, 'Price')

cones.drop('Price')

cones

cones_without_price = cones.drop('Price')
cones_without_price

cones.where('Flavor', 'chocolate')

cones.sort('Price')

cones.sort('Price', descending=True)

cones.sort('Flavor', descending=True)

Example 2: Basketball¶

# From https://github.com/erikgregorywebb/datasets/blob/master/nba-salaries.csv
nba = Table.read_table('nba_salaries.csv')
nba

point_guards = nba.where('position', 'PG').where('season', 2020)

point_guards

point_guards.drop('position')

point_guards

point_guards = point_guards.drop('rank', 'position', 'season')

point_guards.show(10)

point_guards.sort('salary').show(10)

point_guards.sort('salary', descending=True).show(10)

The order of the computations does matter!

Discussion Question: Which one of the following two lines of code fail?

nba.drop('position').where('position', 'PG')

nba.where('position', 'PG').drop('position')