Python Dictionaries Quiz

Dictionaries Introduction

• Dictionaries store related information; they connect pieces of information
• Allow for modification of stored information
• Can store a large amount of data
• Can nest dictionaries inside lists, lists in dictionaries and vice versa.

Understanding Dictionaries

• Model real word objects accurately
• Enables creating dictionaries representing people and storing various information (name, age, etc.)
• Can store pairs of matched information (lists of words and their meanings)
• Unlike lists, tuples or strings, dictionaries are not sequential collections.
• Dictionaries use keys to access values (unorderly, associative collection)
• Keys can be any immutable type (strings, numbers)
• Values can be any Python data object

Dictionary Glossary

• Dictionary: A collection of key-value pairs mapping from keys to values; keys are immutable, values can be of any type.
• Key: A data item mapped to a value in a dictionary. Used to look up values.

Key-Value Pairs

• Pairs of items in a dictionary
• Values looked up by keys.

Mapping Type

• Contains keys and associated values
• Python's built-in mapping type is the dictionary
• Implements associative array abstract data type.

Dictionaries

• Different kind of collection
• Python's built-in mapping type
• Unordered, associative collection
• Key can be any immutable type, value can be any Python data object

Dictionary Operations

• del statement: removes a key-value pair from a dictionary
• Dictionaries are mutable (can be modified), can be changed by assigning values to keys

Dictionary Methods

• keys(): returns a view of dictionary's keys
• values(): returns a view of dictionary's values
• items(): returns a view of key-value pairs
• get() returns the value associated with a key, or None if not found. (alternative return value available)
• update(): adds elements form another dictionary to the dictionary, or updates the dictionary in place

Aliasing & Copying Introduction

• Aliasing: Multiple variables referencing the same dictionary object in memory. Modification in one variable affects all.

• Copying: Creates a new, independent dictionary; original remains unchanged. Modifications to new copy do not change the original.

  • Shallow Copy: Creates new dictionary, values are still references to original. Modifying a nested object affects both copies.
  • Deep Copy: Creates a completely independent copy of the dictionary and its nested objects. Modifying nested objects does not affect the original.

• Understanding these distinctions is important to avoid unwanted outcomes when modifying objects.

Introduction to the join method

• Joins an iterable of strings into a single string separated by a delimiter
• Useful with lists of strings

Join & Dictionaries

• Dictionaries store key-value pairs
• To use the join method on keys/values of a dictionary, the values must all be strings. Convert other types to strings if needed.

Introduction to the split method

• Splits a string into a list of substrings. Use a delimiter (optional); if no delimiter is supplied, whitespace is used by default.
• Return Value: A list of strings

Split & Dictionaries

• Split strings into separate lists to use with dictionaries

Filling a Dictionary with User Input

• Use a while loop to repeatedly ask for user input
• Store the responses in a dictionary, connect each response with a user (e.g. name;mountain to climb)

Looping Through a Dictionary

• Loop through key-value pairs, keys, or values
• Accessing individual key-value pairs inside the loop to retrieve specific data.
• Use descriptive variable names for keys and values

Looping Through Keys in a Particular Order

• Dictionary keys are stored in the same insertion order, though can be looped through in specific order using the sorted function.

Looping Through Dictionary Values

• Getting a list of values from a dictionary; set() is used to create unique items, useful when you need a list of things without repetition that might otherwise contain repeated items