Midterm Tips and Dictionaries 2.0

CS106AP Lecture 14

RoadmapProgramming Basics

The Console Images

Data structures

MidtermGraphics

Object-Oriented Programming

Everyday Python

Life after CS106AP!

Day 1!

Images

The Console

Everyday PythonObject-Oriented Programming

MidtermGraphics

Programming Basics

Roadmap

Life after CS106AP!

Day 1!

Data structures

ListsFilesParsing: Strings

Dictionaries 1.0

Dictionaries 2.0

Nested Data Structures

Today’s questions

How can I effectively prepare for the midterm?

How can I organize and examine my data?

Today’s topics

1. How to Prepare for the Midterm

2. Review

3. Organizing Data

Dictionaries

Built-in Functions

4. What’s next?

Midterm Preparation

Midterm Logistics

● Monday, July 22 7:00-9:00pm at Hewlett 200

○ Please arrive 5-10 minutes early

● If you have an alternate exam, Nick will be in contact about time and

location

● Bring your own laptop! (+ charger)

Midterm Logistics

● Closed-internet

● You are allowed 10 pages (double-sided) of notes

● We will provide a reference sheet of common functions for strings,

lists, dicts, etc.

○ We will publish it with the practice midterm

Midterm Logistics

● You will need to download BlueBook, which is our test-taking software

○ Linked on our home page

● You should test out BlueBook beforehand!

Midterm Practice

● We will publish the practice midterm tomorrow

● Nick will hold a midterm review session Friday 1:30-2:30pm in Gates B1

○ He will recap course content!

Midterm Content

● Material is from Karel to what we cover in lecture today

○ (Wednesday, July 17, Lecture 14)

● Topics: Karel, console programs, strings, images, parsing,

lists, files, dicts

● Types of problems: trace, coding functions

● No Doctests required!

How do I study for the midterm?

● Content Review

○ lecture slides, videos

● Content Application

○ practice exam, section problems, lecture examples

How do I study for the midterm?

● Content Review

○ lecture slides, videos

● Content Application

○ practice exam, section problems, lecture examples

Content Application > Content Review!

Midterm Studying Tips & Tricks

● Practice problems without looking at the solutions

○ practice exam (time yourself!), section problems, lecture examples

○ “I could have figured that out.” Be the change you want to see!

● Creating your notes as a way of reviewing concepts

○ writing by hand can help you remember!

○ summarize materials in your own words or quiz yourself!

If you’re studying and get stuck/get a problem wrong...

● Read over the solution

● Then, come back later and solve the problem again without looking at

the solution

○ “Reps” (repetitions) can help you learn!

If you’re stuck when solving a problem...

If you’re stuck when solving a problem...

● Make a drawing

If you’re stuck when solving a problem...

● Make a drawing

● Write down the inputs and outputs

If you’re stuck when solving a problem...

● Make a drawing

● Write down the inputs and outputs

● Describe in your own words what task you want to accomplish

If you’re stuck when solving a problem...

● Make a drawing

● Write down the inputs and outputs

● Describe in your own words what task you want to accomplish

○ Then use top-down decomposition and/or pseudocode

If you’re stuck when solving a problem...

● Make a drawing

● Write down the inputs and outputs

● Describe in your own words what task you want to accomplish

○ Then use top-down decomposition and/or pseudocode

● Look over the reference sheet and think about what concepts might

help you accomplish that task!

Midterm Strategy

● We don’t mark you down for syntax errors (e.g. typos, missing ‘:’)

unless we can’t tell what you meant.

● We want to give you partial credit!

○ Show your work and describe your thought process even if you’re

not 100% sure

Review

DictionaryA container data type that maps “keys” to their

associated “values”.

Definition

Adapted from Jon Skeet

Anatomy of a Dictionary - Get/Set

>>> d[‘hansa’]

4

this operation is called “get”

dict

‘hansa’‘kandula’‘lumpy’‘surus’

4326

keys values

Anatomy of a Dictionary - Get/Set

>>> d[‘hansa’]

4

>>> d[‘hansa’] = 5

this operation is called “set”

dict

‘hansa’‘kandula’‘lumpy’‘surus’

5326

keys values

Anatomy of a Dictionary - Get/Set

>>> d[‘hansa’]

4

>>> d[‘hansa’] = 5

Note: get and set are fast!

dict

‘hansa’‘kandula’‘lumpy’‘surus’

5326

keys values

Dictionaries + in

>>> ‘hansa’ in d

True

>>> ‘nick’ not in d

True

dict

‘hansa’‘kandula’‘lumpy’‘surus’

5326

keys values

Common pattern:Check if key is present. If it is, do something. If it isn’t, do something else.

Building a Dictionary

>>> d = {}

>>> d[‘hansa’] = 3

>>> d

{‘hansa’: 3}we can add keys using “set”!

create an empty dictionary

Building a Dictionary

>>> d = {‘hansa’: 3}

>>> d[‘hansa’] += 2

>>> d

{‘hansa’: 5}we can get/set on the same line!(same as d[‘hansa’] = d[‘hansa’] + 2)

Summary

>>> d = {} # new dict

>>> d[‘hansa’] = 2 # set

>>> d[‘hansa’] # get

2

>>> ‘hansa’ in d # check membership

True

Think/Pair/Share:Write a program that counts the number of times each word occurs in a file and outputs a word to word_count dict.

Input: filename

How can I organize and examine my data?

Types of Dictionaries

● So far, we’ve seen dictionaries mapping from strings to ints

Types of Dictionaries

● So far, we’ve seen dictionaries mapping from strings to ints

○ This is not the only type of dictionary!

Types of Dictionaries

● So far, we’ve seen dictionaries mapping from strings to ints

○ This is not the only type of dictionary!

○ You can map from string/int/float to string/int/float...

Types of Dictionaries

● So far, we’ve seen dictionaries mapping from strings to ints

○ This is not the only type of dictionary!

○ You can map from string/int/float to string/int/float...

■ ...and more! (coming tomorrow)

Accessing a Dictionary’s Keys

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

Accessing a Dictionary’s Keys

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> d.keys()

Accessing a Dictionary’s Keys

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> d.keys()

dict_keys(['Gates', 'MemChu', 'Tresidder'])

Accessing a Dictionary’s Keys

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> d.keys()

dict_keys(['Gates', 'MemChu', 'Tresidder'])

iterable collection of all the keys.iterable means it can be used in foreach

Accessing a Dictionary’s Keys

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> list(d.keys())

Accessing a Dictionary’s Keys

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> list(d.keys())

[‘Gates’, ‘MemChu’, ‘Tresidder’]

Accessing a Dictionary’s Keys

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> list(d.keys())

[‘Gates’, ‘MemChu’, ‘Tresidder’]

we are using list() to convert d.keys() into a list

Accessing a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

Accessing a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> list(d.values())

Accessing a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> list(d.values()) we are using list() to convert d.values() into a list

Accessing a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> list(d.values())

[23, 116, 57]

we are using list() to convert d.values() into a list

Looping over a Dictionary’s Keys

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

Looping over a Dictionary’s Keys

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building in d.keys():

Looping over a Dictionary’s Keys

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building in d.keys():

... print(building)

Looping over a Dictionary’s Keys

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building in d.keys():

... print(building)

Gates

MemChu

Tresidder

Looping over a Dictionary’s Keys

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building in d.keys():

... print(building)

Gates

MemChu

Tresidder

we can use foreach on the dictionary’s keys!

Looping over a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

Looping over a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for age in d.values():

Looping over a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for age in d.values():

... print(age)

Looping over a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for age in d.values():

... print(age)

23

116

57

Looping over a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for age in d.values():

... print(age)

23

116

57

we can use foreach on the dictionary’s values!

Looping over a Dictionary’s Keys and Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

Looping over a Dictionary’s Keys and Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building, age in d.items():

Looping over a Dictionary’s Keys and Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building, age in d.items():items() gives us key, value pairs

Looping over a Dictionary’s Keys and Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building, age in d.items():

... print(building, ‘is’, age, ‘years old.’)

items() gives us key, value pairs

Looping over a Dictionary’s Keys and Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building, age in d.items():

... print(building, ‘is’, age, ‘years old.’)

Gates is 23 years old.

MemChu is 116 years old.

Tresidder is 57 years old.

items() gives us key, value pairs

Looping over a Dictionary’s Keys and Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building, age in d.items():

... print(building, ‘is’, age, ‘years old.’)

Gates is 23 years old.

MemChu is 116 years old.

Tresidder is 57 years old.

print() will automatically concatenate args separated by commas!

Printing with sep=

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building, age in d.items():

... print(building, age, sep=‘: ’)

Printing with sep=

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building, age in d.items():

... print(building, age, sep=‘: ’)

sep is an optional argument like end!

Printing with sep=

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building, age in d.items():

... print(building, age, sep=‘: ’)

Gates: 23

MemChu: 116

Tresidder: 57

sep is an optional argument like end!

Printing with sep=

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building, age in d.items():

... print(building, age, sep=‘: ’)

Gates: 23

MemChu: 116

Tresidder: 57

the separating string will be printed between the arguments you pass into print()

Printing with sep=

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> for building, age in d.items():

... print(building, age, sep=‘: ’)

Gates: 23

MemChu: 116

Tresidder: 57

the default is sep=‘ ’(insert space)

Getting a Sorted List of Keys

>>>d = {‘Gates’: 23, ‘Tresidder’: 57, ‘MemChu’: 116}

Getting a Sorted List of Keys

>>> d = {‘Gates’: 23, ‘Tresidder’: 57, ‘MemChu’: 116}

>>> sorted(d.keys())

Getting a Sorted List of Keys

>>> d = {‘Gates’: 23, ‘Tresidder’: 57, ‘MemChu’: 116}

>>> sorted(d.keys())

['Gates', 'MemChu', 'Tresidder']

Getting a Sorted List of Keys

>>> d = {‘Gates’: 23, ‘Tresidder’: 57, ‘MemChu’: 116}

>>> sorted(d.keys())

['Gates', 'MemChu', 'Tresidder']

sorted() returns a list in alphabetical order!

Getting a Sorted List of Keys

>>> d = {‘Gates’: 23, ‘Tresidder’: 57, ‘MemChu’: 116}

>>> sorted(d.keys())

['Gates', 'MemChu', 'Tresidder']

>>> d

Getting a Sorted List of Keys

>>> d = {‘Gates’: 23, ‘Tresidder’: 57, ‘MemChu’: 116}

>>> sorted(d.keys())

['Gates', 'MemChu', 'Tresidder']

>>> d

{‘Gates’: 23, ‘Tresidder’: 57, ‘MemChu’: 116}

Sorting a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

Sorting a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> sorted(d.values())

Sorting a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> sorted(d.values())

[23, 57, 116]

Sorting a Dictionary’s Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> sorted(d.values())

[23, 57, 116]

sorted() returns a list in numerical order!

Retrieving Min/Max Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

Retrieving Min/Max Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> min(d.values())

Retrieving Min/Max Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> min(d.values())

returns the smallest element!

Retrieving Min/Max Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> min(d.values())

23 returns the smallest element!

Retrieving Min/Max Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> min(d.values())

23

>>> max(d.values())

returns the smallest element!

Retrieving Min/Max Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> min(d.values())

23

>>> max(d.values())

returns the smallest element!

returns the biggest element!

Retrieving Min/Max Values

>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}

>>> min(d.values())

23

>>> max(d.values())

116

returns the smallest element!

returns the biggest element!

Built-in FunctionA function built into Python that is always

available for use.

Definition

Examples of Built-ins

print()input()str()int()float()len()

open()list()sorted()max()min()

Examples of Built-ins

print()input()str()int()float()len()

open()list()sorted()max()min()

What’s next?

What’s next?

dict

‘hansa’‘kandula’‘lumpy’‘surus’

keys values

Image from Allie Brosh

Images

The Console

Everyday PythonObject-Oriented Programming

MidtermGraphics

Programming Basics

Roadmap

Life after CS106AP!

Day 1!

Data structures

ListsFilesParsing: Strings

Dictionaries 1.0

Dictionaries 2.0

Nested Data Structures