Dictionaries

Intermediate Python for Finance

Kennedy Behrman

Data Engineer, Author, Founder

Lookup by index

my_list = ['a','b','c','d']

  0   1   2   3
['a','b','c','d']

my_list[0]

'a'

my_list.index('c')

Lookup by key

Dictionaries

Diagram of keys pointing to values

Representation

{ 'key-1':'value-1', 'key-2':'value-2', 'key-3':'value-3'}

Creating dictionaries

my_dict = {}
my_dict

{}

my_dict = dict()
my_dict

{}

Creating dictionaries

ticker_symbols = {'AAPL':'Apple', 'F':'Ford', 'LUV':'Southwest'}
print(ticker_symbols)

{'AAPL':'Apple', 'F':'Ford', 'LUV':'Southwest'}

ticker_symbols = dict([['APPL','Apple'],['F','Ford'],['LUV','Southwest']])
print(ticker_symbols)

{'AAPL':'Apple', 'F':'Ford', 'LUV':'Southwest'}

Adding to dictionaries

ticker_symbols['XON'] = 'Exxon'
ticker_symbols

{'APPL': 'Apple', 'F': 'Ford', 'LUV': 'Southwest', 'XON': 'Exxon'}

ticker_symbols['XON'] = 'Exxon OLD'
ticker_symbols

{'APPL': 'Apple','F': 'Ford','LUV': 'Southwest','XON': 'Exxon OLD'}

Accessing values

ticker_symbols['F']

'Ford'

Accessing values

ticker_symbols['XOM']

KeyError                                  Traceback (most recent call last)
<ipython-input-6-782fbf617bf7> in <module>()
-> 1 ticker_symbols['XOM']

   KeyError: 'XOM'

Accessing values

company = ticker_symbols.get('LUV')
print(company)

'Southwest'

company = ticker_symbols.get('XOM')
print(company)

None

company = ticker_symbols.get('XOM', 'MISSING')
print(company)

'MISSING'

Deleting from dictionaries

ticker_symbols

{'APPL': 'Apple', 'F': 'Ford', 'LUV': 'Southwest', 'XON': 'Exxon OLD'}

del(ticker_symbols['XON'])

ticker_symbols

{'APPL': 'Apple', 'F': 'Ford', 'LUV': 'Southwest'}

Let's practice!

Intermediate Python for Finance