Dictionaries
Lists
my_list = ['a','b','c','d'] # index 0 1 2 3 my_list[0] > 'a' my_list.index['c'] > 2
Intro
Keys Values ---- ------ Firm Code FRD Process Date 10/14/2019 CUSIP 13246879
Representation of a dictionary = { ‘key-1’ : ‘value-1’ , ‘key-2’ : ‘value-2’ , ‘key-3’ : ‘value-3’ , ‘key-4’ : ‘value-4’ }
Creation
# Create an empty dict
my_dict = {}
my_dict
> {}
# native
tickersymbols = {'AAPL':'Apple', 'F':'Ford', 'XON':'Exxon'}
> {'AAPL': 'Apple', 'F': 'Ford', 'XON': 'Exxon'}
# OR by lists
tickersymbols = dict([['AAPL','Apple'],['F','Ford'],['XON','Exxon']])
> {'AAPL': 'Apple', 'F': 'Ford', 'XON': 'Exxon'}
Handling a dictionary
# Adding
tickersymbols['TSLA'] = 'Tesla'
tickersymbols
> {'AAPL': 'Apple', 'F': 'Ford', 'XON': 'Exxon', 'TSLA': 'Tesla'}
# Update
tickersymbols['TSLA'] = 'Tesla_Inc'
tickersymbols
> {'AAPL': 'Apple', 'F': 'Ford', 'XON': 'Exxon', 'TSLA': 'Tesla_Inc'}
# Deleting an entry
del(tickersymbols['F'])
tickersymbols
> {'AAPL': 'Apple', 'XON': 'Exxon', 'TSLA': 'Tesla_Inc'}
Accessing
# Entry in dict
tickersymbols['XON']
> 'Exxon'
# No entry in dict
tickersymbols['IBM']
> KeyError: 'IBM'
# Second method
tickersymbols.get('XON')
> 'Exxon'
tickersymbols.get('IBM')
> (nothing)
tickersymbols.get('IBM','Missing ticker')
> 'Missing ticker'
Examples
from datetime import datetime, timedelta
alphabet_hist = {datetime.datetime(2019, 7, 30, 0, 0): 1228, datetime.datetime(2019, 7, 31, 0, 0): 1218.2, datetime.datetime(2019, 8, 1, 0, 0): 1211.78, datetime.datetime(2019, 8, 2, 0, 0): 1196.32}
closing_price_date = datetime.datetime(2019, 8, 2, 0, 0)
# Closing price for day before
day_before_closing_price_date = closing_price_date - timedelta(days=1)
# Safely print closing price day before or None if it's missing
print(alphabet_hist.get(day_before_closing_price_date))
> 1211.78
# Get day eight weeks in future
future_closing_price_date = closing_price_date + timedelta(weeks=8)
# Safely get value for the future date or the string 'Missing'
print(alphabet_hist.get(future_closing_price_date, 'Missing'))
> Missing
# Print with key
print(alphabet_hist)
> {datetime.datetime(2019, 8, 2, 0, 0): 1196.32, datetime.datetime(2019, 8, 1, 0, 0): 1211.78, datetime.datetime(2019, 7, 31, 0, 0): 1218.2, datetime.datetime(2019, 7, 30, 0, 0): 1228}
# Remove entry
del(alphabet_hist[closing_price_date])
# Print with key deleted
print(alphabet_hist)
> {datetime.datetime(2019, 8, 1, 0, 0): 1211.78, datetime.datetime(2019, 7, 31, 0, 0): 1218.2, datetime.datetime(2019, 7, 30, 0, 0): 1228}