Key Ideas

  • Keys
    • To retrieve all keys in a dictionary named inventory: inventory.keys()
    • To retrieve all keys as a list: list(inventory.keys())
    • To retrieve keys one at a time: for key in inventory:
    • To check if a key named "kiwi" exists: if "kiwi" in inventory:
  • Values
    • To retrieve all values: inventory.values()
    • To retrieve a specific value, producing a runtime error if the key is not present: inventory[key-name]
    • To retrieve a specific value, producing NO runtime error if the key is not present: inventory.get(key-name) or inventory.get(key-name, value-to-return-if-key-not-present)
  • Key-Value Pairs
    • To retrieve all key-value pairs: inventory.items()
  • Aliasing vs. Copying
    • An example of an alias: dictionary1 = dictionary2
    • The expression dictionary2 is dictionary1 #returns True
    • An example of a copy: dictionary2 = dictionary1.copy()
    • The expression dictionary2 is dictionary1 #returns False

In-Class Learning

  • Edit ebird_problem.py so the program use the data in the mt_recents dictionary to create a csv file called ebird_recent.csv. (Hint: you’ll probably want to use list(mt_recents.keys()) (see above in Key Ideas).
# ebird_problem.py
mt_recents = {
                'speciesCode': 'houspa', 
                'comName': 'House Sparrow', 
                'sciName': 'Passer domesticus', 
                'locId': 'L17967461', 
                'locName': 'Casita Del Rio', 
                'obsDt': '2022-03-01 09:49', 
                'howMany': 10, 
                'lat': 47.101325, 
                'lng': -104.730941, 
                'obsValid': True, 
                'obsReviewed': False, 
                'locationPrivate': True,
              }

# create header
labels = list(mt_recents.keys())    # create list of all keys
header = ", ".join(labels)          # create csv string of labels

# create data line
data = []              # create empty list to store values
for item in labels:    # iterate through list of keys
    data += [str(mt_recents[item])] # append value to data list
data_line = ", ".join(data)     # create csv string of data

# write to csv file
output = open("recent.csv", "w")    # create file object
output.write(header + "\n")         # write header to file
output.write(data_line + "\n")      # write data to file

output.close()

Active Learning

  • Write a program that allows the user to enter a string. It then prints a table of the letters of the alphabet in alphabetical order which occur in the string together with the number of times each letter occurs. Case should be ignored. A sample run of the program might look this this:
Please enter a sentence: ThiS is String with Upper and lower case Letters.
a  2
c  1
d  1
e  5
g  1
h  2
i  4
l  2
n  2
o  1
p  2
r  4
s  5
t  5
u  1
w  2

# ex1.py

import string

sentence = input("Please enter a sentence: ")

letters = {}

for character in sentence.lower():
    if character in string.ascii_lowercase:
        letters[character] = letters.get(character, 0) + 1

for character in sorted(letters.keys()):
    print("{}  {}".format(character, letters[character]))
  • Give the Python interpreter’s response to each of the following from a continuous interpreter session:
>>> d = {'apples': 15, 'bananas': 35, 'grapes': 12}
>>> d['banana']

>>> d['oranges'] = 20
>>> len(d)

>>> 'grapes' in d

>>> d['pears']

>>> d.get('pears', 0)

>>> fruits = d.keys()
>>> fruits.sort()
>>> print(fruits)

>>> del d['apples']
>>> 'apples' in d