Lec18

Lec18, Wed 03/04

Questions

Question: Why would you just want to store one object in a tuple?
Ans: If you store stuff in a tuple, the object will not change.

def printPet(aDict, key):
  age = aDict[key]['age']
  pettype = aDict[key]['type']
  date = aDect[key]['date']
  format_str = "{} is a {} who is {} old and we got it on {}"
  print(format_str.format(key, pettype, age, date))

'''
Output:
printPet(pets,'Cutie')
Cutie is a poddle who is 3 months old and we got it on 03/04/2020
'''

Slicing iClicker Questions

>>> title = "Miss America"
>>> print( ??? )
'America'

Answer: B

print(title[5:])

>>> mylist = [11, 12, 81, 88, 123]
>>> print( ??? )
[81, 88]

Answer: C

print(myList[2:4])

** Question: If I put endpoint as len(myList), would it include the last character? **

Answer: Yes, it will include it because the length of a list or string will always be one more than the number corresponding to the last index

Tips and questions to consider for the recursive substring problem:

You can have multiple base cases!
What is the simplest case for this problem?
If your substring is longer than your string, what should you do?
What if the lengths are the same, what can you do?
What about if neither of those are true? You can start slicing off characters of the string and continue to compare…

Dictionaries

** Question: What are dictionaries good for? **

Answer:
- If we used a list, we would have to store each key and value pair as a list within a list. Then it will be difficult to pull out the information I want for certain things. I would have to loop through the list until I found the value that I want.
- Dictionaries make it much easier to find the values we need.
- It would make searching for things much faster.
- We wouldn’t have to worry about storing the index for something.
- The order/indexing doesn’t matter for the keys.

** Question: Does it have to be in a certain order if we are storing multiple things for each key in the dictionary? **

Example of a nested dictionary

lets store the type of each cookie, the price of each cookie, the calories in each cookie, and number of cookies we have.

cookieType = ['chocolate chip', 'macnut cookie', 'peanut butter']
cookiePrice = ['$20','$30', '$3']
caloriesPerCookie = [112, 200, 1000]
numOfEachCookie = [3,15, 2001]

def printCookie(index, cookieType, cookiePrice, caloriesPerCookie, numOfEachCookie):
    format_str = "The cookie {} ({} items) has {} calories, costs {}"
    print(format_str.format(cookieType[index], cookiePrice[index], numOfEachCookie[index], caloriesPerCookie[index]))

This is kind of messy… Lets try using a dictionary

cookies = {'chocolate chip': {'price': '$20',
                                 'amount': 3,
                                 'calories': 112},
           
              'macnut cookie': {'price': '$30',
                                'amount': 15,
                                'calories': 200},
              
              'peanut butter': {'price': '$3',
                                'amount': 2001,
                                'calories':1000}
              }

def printCookie( cookieD, key):
    format_str = "The cookie {} ({} items) has {} calories, costs {}"
    name = key
    price = cookieD[key]["price"]
    amount = cookieD[key]["amount"]
    calories = cookieD[key]["calories"]
    print(format_str.format(name, amount, calories, price))

** Question: Could you change the calories and amount to be a string? **

Answer: Yes, but leaving it as an integer allows us to more easily do math if we wanted to add more cookies later on.

** Question: How can we add a new cookie to the dictionary? **

 cookies["mint chocolate"] = {'price': '$5',
                                 'amount': 10,
                                 'calories': 435}

Also, notice that we don’t have to have all of the information in there. For example, if we did not know the calories, we could just leave it out like so:

cookies["oatmeal raisin"] = {'price': '$0',
                                 'amount': 367}

Named Tuples

from collections import namedtuple
# Design your named tuple object
Student = namedtuple('Student', 'name perm major')
# create new objects of type Student
s1 = Student("Olivia", 1234567, "CS")
# Access the elements of the object:
print(s1.name, s1.perm, s1.major, sep = " ")

>>> Cookie = namedTuple("Cookie", 'name price amount calories')
>>> c1 = Cookie("chocolate chip",'$20', 3, 112)
>>> c1.name
'chocolate chip'
>>> c1.calories
112

def printCookie( ntuple ):
    format_str = "The cookie {} ({} items) has {} calories, costs {}"
    name = ntuple.name
    price = ntuple.price
    amount = ntuple.amount
    calories = ntuple.calories
    print(format_str.format(name, amount, calories, price))