Python List Methods Quiz

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Questions and Answers

What does the sort method do to a list?

Mutates the list by arranging its elements in descending order

Returns a sorted copy of the list

Mutates the list by arranging its elements in ascending order (correct)

Creates a new list without changing the original

What is the result of calling a mutator method like sort on a list?

The list is unchanged and the original list reference is returned

The original list is returned with a sorted order

The original list is modified and the value None is returned (correct)

A new list containing the sorted elements is returned

What occurs when two variables point to the same list object?

Both variables are aliases and refer to the same list (correct)

They can only point to lists of the same size

Changing one variable will not affect the other

Both variables can hold different lists eventually

What should you do to prevent aliasing when copying a list?

Create a new list and append each element from the original Signup and view all the answers

Which of the following statements about the sort method is correct?

It can sort a list of different data types together Signup and view all the answers

What does the == operator indicate when comparing two variables in Python?

It checks if two variables are the same plus if their contents are also equal. Signup and view all the answers

Which operator in Python is specifically used to test for object identity?

is operator Signup and view all the answers

Based on the example provided, what will be the result of comparing 'first' and 'third' using the is operator?

False Signup and view all the answers

When determining the median of a set of numbers, which of the following is a necessary step?

Sort the numbers in ascending order. Signup and view all the answers

What can be inferred about the relations checked by the == and is operators in Python?

The == operator checks for structural equivalence, while the is operator checks for object identity. Signup and view all the answers

What allows a programmer to manipulate a sequence of data values of any type?

List Signup and view all the answers

What is the primary structural difference between a list and a dictionary?

Lists organize data by sequential position, while dictionaries use associations. Signup and view all the answers

Which operation is not typically associated with lists?

Key-value association Signup and view all the answers

In which scenario would a dictionary be more appropriate than a list?

When you need to easily locate a value by a known key. Signup and view all the answers

What might be a consequence of using a list in a situation requiring key-value pairs?

Data will require additional processing. Signup and view all the answers

What does the is operator check in Python?

Whether two variables refer to the same object. Signup and view all the answers

What will the expression 'first == second' evaluate to in the provided example?

True Signup and view all the answers

What is indicated when 'first is third' evaluates to False?

First and third reference separate list objects. Signup and view all the answers

Why can the == operator be ambiguous when comparing two objects?

It cannot determine if the objects are identical or just structurally equivalent. Signup and view all the answers

What is the purpose of using a list in finding the median of a set of numbers?

To allow easy access and modification of elements during calculation. Signup and view all the answers

What does the expression '3 in [1, 2, 3]' evaluate to?

True Signup and view all the answers

How can you replace the first element of the list 'example = [1, 2, 3, 4]' with the value 0?

example[0] = 0 Signup and view all the answers

What will the list 'numbers' contain after executing the loop with 'numbers = [2, 3, 4, 5]'?

[4, 9, 16, 25] Signup and view all the answers

What does the method 'split()' do when called on a string?

It splits the string into a list of words. Signup and view all the answers

After executing 'words[index] = words[index].upper()' on the list of words extracted from the sentence, what will 'words' contain?

['THIS', 'EXAMPLE', 'HAS', 'FIVE', 'WORDS.'] Signup and view all the answers

What does the method L.append(element) accomplish?

Adds element to the end of L Signup and view all the answers

What happens when you use L.insert(index, element) with an index greater than the length of L?

The element is added at the end of L Signup and view all the answers

What is the purpose of the method L.extend(aList)?

Adds individual elements of aList to the end of L Signup and view all the answers

What does the method L.pop(index) return?

The element at the specified index and removes it from L Signup and view all the answers

Given the example list [1, 2], what will the list be after example.insert(1, 10)?

[1, 10, 2] Signup and view all the answers

Study Notes

Fundamentals of Python: First Programs - Second Edition

This is a Python programming textbook, second edition
Chapter 5 focuses on lists and dictionaries

Chapter 5: Lists and Dictionaries

Objectives (Part 1 of 2):
- Construct lists and access items
- Use methods to manipulate lists
- Perform traversals of lists
- Define simple functions expecting parameters and returning values
Objectives (Part 2 of 2):
- Construct dictionaries and access entries
- Use methods to manipulate dictionaries
- Determine whether a list or a dictionary is appropriate for a given application

Introduction

Lists manipulate sequences of any data type
Dictionaries organize data values by association rather than sequential position
Lists and dictionaries efficiently organize data for applications

Lists

Lists are ordered sequences of items (elements)
Examples include shopping lists, to-do lists, rosters, guest lists, recipes, text documents, and phone books
Each list item has a unique index (position from 0 to length - 1)

List Literals and Basic Operators (Part 1 of 4)

Examples of list literals include: ['apples', 'oranges', 'cherries'], [[5, 9], [541, 78]]
Elements within a list can be expressions, whose values are calculated and included in the list
Example: [x, math.sqrt(x)] where x = 2 results in [2, 1.4142135623730951]

List Literals and Basic Operators (Part 2 of 4)

Building lists of integers using the range function
Example, first =[1, 2, 3, 4] and second = list(range(1, 5)) both result in the same list [1,2,3,4]
The list function creates a list from an iterable sequence of elements
Example, list("Hi there!" results in ['H', 'i', '', 't', 'h', 'e', 'r', 'e', '!']

List Literals and Basic Operators (Part 3 of 4)

The len function, square brackets, the plus sign (+), and the equals sign (==) operate on lists as expected
Example of list concatenation (using +): first + [5, 6] results in [1, 2, 3, 4, 5, 6]
Example of list equality (using ==): first == second results in True

List Literals and Basic Operators (Part 4 of 4)

Printing list contents:
Example, print(“1234”) will print "1234"; print([1, 2, 3, 4]) will print [1, 2, 3, 4]
Using the in operator to check for an element:
Example, 3 in [1, 2, 3] returns True; 0 in [1, 2, 3] returns False

Replacing an Element in a List (Part 1 of 2)

Lists are mutable. Elements can be inserted, removed, or replaced
Contents of a list can change but its identity remains the same.
Using the subscript operator to replace an element:
Example, example = [1, 2, 3, 4] --> example[3] = 0 --> example = [1, 2, 3, 0]

Replacing an Element in a List (Part 2 of 2)

Replacing elements in a list based on an index and using string method .split()
Examples, [2,3,4,5] to [4,9,16,25]; and “This example has five words.” to ["THIS", "EXAMPLE", "HAS", "FIVE", "WORDS."]

List Methods for Inserting and Removing Elements (Part 1 of 4)

Summary table of list methods explaining the effect of each method on the list

List Methods for Inserting and Removing Elements (Part 2 of 4)

Method insert to insert an integer index and a new element. Example adding 10 in index 1 results in [1,10,2]

List Methods for Inserting and Removing Elements (Part 3 of 4)

Method append to add a new element to the end of the list
Method extend to add the elements from another list to the end of a list

List Methods for Inserting and Removing Elements (Part 4 of 4)

Method pop to remove an element
Example removing last element from [1, 2, 10, 11, 12,13] results in [1, 2, 10, 11, 12]; removing the first results in [10, 11, 12]

Searching a List

The in operator determines if an element exists in a list.
Method index locates an element's position. Raises an error if the element is not found
Example: aList = [34, 45, 67], target = 45, if target in aList: print(aList.index(target)) else: print(-1)

Sorting a List

List elements are ordered by position; can be sorted alphabetically
Method sort rearranges list elements in ascending order. Example: example = [4, 2, 10, 8] -> example.sort() -> example = [2, 4, 8, 10]

Mutator Methods and the Value None

Mutator methods (insert, append, extend, pop, and sort) change a list
Python returns None after the mutator methods are executed

Aliasing and Side Effects (Part 1 of 2)

Lists have a mutable property: aliasing can lead to unexpected results
Two variables (first and second), referencing the same list object. Changing one affects the other example, [1,2,3] -> [1,99,3] which also changes the second variable holding the same data.

Aliasing and Side Effects (Part 2 of 2)

Creating a new object to prevent aliasing, copying the contents of one list object to a new list object.
Example third = [] for element in first: third.append(element) changes values independent in variables.

Equality: Object Identity and Structural Equivalence (Part 1 of 2)

Programmers determine whether variables refer to the same object or different objects
== operator returns true if variables are aliases
== returns true if values are identical
The issue with the == operator is its inability to distinguish between type of equivalence.

Equality: Object Identity and Structural Equivalence (Part 2 of 2)

Use the is operator for testing object identity
Example: first = [20, 30, 40]; second = first; third = list(first); first == second returns true; first == third returns true; first is second returns true; first is third returns false.

Example: Using a List to Find the Median of a Set of Numbers

Python code to find the median of a list of numbers

Tuples

Tuples are similar to lists but immutable, indicated by enclosing elements in parenthesis -Example: fruits = (“apple”, “banana”)

Defining Simple Functions

Defining functions helps organize code effectively in Python programs
Section provides an overview of how to define Python functions

The Syntax of Simple Function Definitions

Function definitions consist of header and body
Example function: def square(x): """Returns the square of x.""" return x * x
To view help, use help(square)

Parameters and Arguments

Parameters are names used in function definitions
Arguments are values passed to functions when called
Functions expect arguments matching parameter structure

The Return Statement

The return statement specifies value(s) function returns
A function without a return statement returns None

Boolean Functions

Boolean functions test arguments for properties
Example: def odd(x): if x % 2 == 1: return True; else: return False

Defining a Main Function (Part 1 of 2)

Main serves as the entry point for a Python script
Typically has no arguments and returns no values; can have definition before other functions
Code can be run in IDLE, imported into the shell, or run from a terminal command prompt

Defining a Main Function (Part 2 of 2)

Example of a main function in Python code

Dictionaries

Dictionaries organize information by association
Keys map unique data values
- Example a phone book with names and numbers; personal information with name, age

Dictionary Literals

Python dictionaries use key-value pairs enclosed in curly brackets {}
Keys are associated with data values. Example a phone book with names as key and number as value

Adding Keys and Replacing Values

Using square brackets [] adds new key-value pairs or replaces existing values.
Example: info = {}; info[“name”] = “Sandy”; info[“occupation”] = “hacker”

Accessing Values (Part 1 of 2)

Use square brackets [] to access dictionary values associated with keys
Raises an error if the key is not found example: Trying to get info["job"] when the key "job" was not defined

Accessing Values (Part 2 of 2)

Use the has_key method to test whether a key exists.
The get() method returns a default value if a key is not found

Removing Keys

Delete entries from dictionaries using the pop method
Example: print(info.pop(“occupation”))

Traversing a Dictionary (Part 1 of 3)

Print all keys and values: for key in info: print(key, info[key])
Alternative, using the items() method. Example: grades = {90:'A', 80:'B', 70:'C'}; list(grades.items()) , which results in tuples [(80, 'B'),(90, 'A'),( 70, 'C')]

Traversing a Dictionary (Part 2 of 3)

Sorting the list of keys from the dictionary example print all keys and values in alphabetical order: theKeys = list(info.keys()); theKeys.sort() for key in theKeys: print(key, info[key]).

Traversing a Dictionary (Part 3 of 3)

Summary table of dictionary operations (len, [], get, pop, keys(), values(), items(), clear)

Chapter Summary (Part 1 of 2)

Recap of list properties (sequence of elements, mutable, indexable, concatenation, comparison, in operator
How lists and sort methods work.
Mutator methods change the state of an object.

Chapter Summary (Part 2 of 2)

Recap of tuples
Syntax of function definitions, return statements
Definition of dictionaries and use of square brackets []
How testing can be done (bottom-up, top-down, or mixed approach)

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Description

Test your knowledge on Python list methods and comparison operators with this quiz. You will explore the workings of the sort method, mutator methods, and the differences between the == and is operators. Understand how list aliasing affects variable references and how to properly manage list copying.