Methods and functions

Introduction to Python for Finance

Adina Howe

Instructor

Methods vs. Functions

Methods

All methods are functions
List methods are a subset of built-in functions in Python

Functions

Not all functions are methods

Used on an object
- prices.sort()

Requires an input of an object
- type(prices)

List Methods - sort

Lists have several built-in methods that can help retrieve and manipulate data
Methods can be accessed as list.method()

list.sort() sorts list elements in ascending order

prices = [238.11, 237.81, 238.91]

prices.sort()

print(prices)

[237.81, 238.11, 238.91]

Adding to a list with append and extend

list.append() adds a single element to a list

months = ['January', 'February', 'March']

months.append('April')

print(months)

['January', 'February', 'March', 'April']

list.extend() adds each element to a list

months.extend(['May', 'June', 'July'])

print(months)

['January', 'February', 'March', 'April', 'May', 'June', 'July']

Useful list methods - index

list.index(x) returns the lowest index where the element x appears

months = ['January', 'February', 'March']
prices = [238.11, 237.81, 238.91]

months.index('February')

print(prices[1])

237.81

More functions ...

min(list): returns the smallest element
max(list): returns the largest element

Find the month with smallest CPI

months = ['January', 'February', 'March']
prices = [238.11, 237.81, 238.91]

# Identify min price
min_price = min(prices)

# Identify min price index
min_index = prices.index(min_price)

# Identify the month with min price
min_month = months[min_index]
print(min_month)

February

Let's practice!

Introduction to Python for Finance