Fundamentals of Python: First Programs - Chapter 5
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Questions and Answers

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

  • They are identical objects.
  • They perform an identity check.
  • They refer to the same memory location.
  • They contain the same data. (correct)

    • Which operator should be used in Python to test for object identity?

  • equals_variable
  • equals
  • is (correct)
  • ==

    • If two variables 'first' and 'second' are assigned like 'second = first', what is true about 'first' and 'second'?

  • They reference two separate objects.
  • They contain identical data structures.
  • They have different memory locations.
  • They are aliases for the same object. (correct)

    • What would 'first is third' return if 'third' is created as 'third = list(first)'?

    <p>False, as they refer to different objects.</p> Signup and view all the answers

    Which of the following statements about object identity and structural equivalence is true?

    <p>Object identity checks whether variables refer to the same object.</p> Signup and view all the answers

    What is a primary characteristic of a list in Python?

    <p>It allows manipulation of a sequence of data values of any types.</p> Signup and view all the answers

    Which method would you use to add an item to the end of a list?

    <p>append()</p> Signup and view all the answers

    How does a dictionary differ from a list?

    <p>A dictionary stores data in key-value pairs.</p> Signup and view all the answers

    When would a dictionary be a more appropriate data structure than a list?

    <p>When you need to associate unique keys with values.</p> Signup and view all the answers

    What does performing a traversal of a list typically involve?

    <p>Iterating through the elements for processing.</p> Signup and view all the answers

    Which of the following is a function of a list in Python?

    <p>Sorting values in ascending order.</p> Signup and view all the answers

    What does the term 'key-value pair' refer to in the context of dictionaries?

    <p>Two related data elements where one is used to access the other.</p> Signup and view all the answers

    Which operation would likely be less efficient when performed on a list compared to a dictionary?

    <p>Searching for an element by value.</p> Signup and view all the answers

    What is the expected behavior of the main function in a typical script?

    <p>It usually expects no arguments and returns no value.</p> Signup and view all the answers

    How can a Python script containing a main function be executed?

    <p>From IDLE, imported into the shell, or run from a terminal command prompt.</p> Signup and view all the answers

    Where can the definition of the main function appear in a script?

    <p>In no particular order, as long as it's called at the end.</p> Signup and view all the answers

    In the example provided, what does the square function do?

    <p>Returns the square of the input number.</p> Signup and view all the answers

    What distinguishes a dictionary from other data structures, according to the provided content?

    <p>It organizes data by association rather than position.</p> Signup and view all the answers

    What is another term for data structures organized by association, mentioned in the content?

    <p>Association lists.</p> Signup and view all the answers

    In the context of the main function, what is the significance of the line 'if name == "main":'?

    <p>It prevents the main function from running when the script is imported.</p> Signup and view all the answers

    What key feature do dictionaries in Python provide?

    <p>Associates a set of keys with corresponding data values.</p> Signup and view all the answers

    What is the correct syntax for adding a new key/value pair to a dictionary in Python?

    <p>dictionary['key'] = 'value'</p> Signup and view all the answers

    What character is used to separate keys and values in a Python dictionary?

    <p>:</p> Signup and view all the answers

    Which of the following describes the type of elements allowed as dictionary keys?

    <p>Any immutable type</p> Signup and view all the answers

    What error occurs if you try to access a key that does not exist in a dictionary?

    <p>KeyError</p> Signup and view all the answers

    What method can be used to safely access a dictionary value without raising an error if the key is absent?

    <p>get()</p> Signup and view all the answers

    Which of the following pairs would correctly represent a phone book entry in a Python dictionary?

    <p>{‘John’: ‘555-1212’}</p> Signup and view all the answers

    What happens to an existing value when you assign a new value to an existing key in a dictionary?

    <p>The existing value is replaced by the new value.</p> Signup and view all the answers

    What will be the output of info['name'] if info is defined as {'name': 'Sandy'}?

    <p>Sandy</p> Signup and view all the answers

    What will happen if you use the insert method with an index greater than the current length of the list?

    <p>The element will be appended to the end of the list.</p> Signup and view all the answers

    What does the method 'L.pop()' do?

    <p>Removes and returns the element at the end of the list.</p> Signup and view all the answers

    When using the method 'L.extend(aList)', what is the effect on the list L?

    <p>It adds all elements from aList to the end of L.</p> Signup and view all the answers

    What is the expected argument type for the index parameter of the insert method?

    <p>Integer</p> Signup and view all the answers

    If the list 'example' is defined as [1, 2] and 'example.insert(1, 10)' is called, what will the new state of 'example' be?

    <p>[1, 10, 2]</p> Signup and view all the answers

    If you call 'L.pop(index)' where index is out of bounds, what will occur?

    <p>An error will be raised.</p> Signup and view all the answers

    What is the result of calling 'example.append(25)' on the list that currently is [1, 10, 2]?

    <p>[1, 10, 2, 25]</p> Signup and view all the answers

    Which of the following methods can be used to add multiple elements from another list to an existing list?

    <p>L.extend(aList)</p> Signup and view all the answers

    What does the method append do in a list?

    <p>Adds a new element to the end of the list.</p> Signup and view all the answers

    What is the difference between append and extend?

    <p><code>extend</code> adds multiple elements from another list.</p> Signup and view all the answers

    What does the method pop do?

    <p>Removes and returns the last element of the list.</p> Signup and view all the answers

    How can you find the position of an element in a list?

    <p>Using the <code>index</code> method.</p> Signup and view all the answers

    What will happen if you use the index method on an element that doesn't exist in the list?

    <p>It will raise an error.</p> Signup and view all the answers

    Which statement is true regarding the in operator?

    <p>It determines the presence of an element in the list.</p> Signup and view all the answers

    What will the list example be after performing example.pop(0) on the list [2, 10, 11, 12]?

    <p>[2, 10, 11]</p> Signup and view all the answers

    What is the expected result of the operation example + [14, 15] where example = [1, 2, 3, 11, 12, 13]?

    <p>[1, 2, 3, 11, 12, 13, 14, 15]</p> Signup and view all the answers

    Study Notes

    Fundamentals of Python: First Programs - Chapter 5

    • Lists and Dictionaries
      • Lists are sequences of data values (items or elements) with examples such as shopping lists, to-do lists, rosters, guest lists, recipes, text documents, and phone books.
      • Each list item has a unique index, starting from 0 and going up to length - 1.
      • List literals can include expressions. For example, [5, 9], [541, 78] or ['apples', 'oranges', 'cherries'].
      • Integers can be built using the range function, such as list(range(1, 5)), resulting in [1, 2, 3, 4].
      • The list function creates a list from an iterable sequence. An example is list("Hi there!"), producing ['H', 'I', ' ', 't', 'h', 'e', 'r', 'e', '!'].
      • The len function, square brackets [], plus +, and equal == work on lists as expected.
      • The in operator detects an element's presence within a list (True or False).
      • Lists are mutable, allowing for inserting, removing, or replacing elements. The list's identity is maintained but its state (length and contents) can change.
      • The subscript operator [] is used to replace an element.
      • Example >>> example = [1, 2, 3, 4], >>> example[3] = 0, >>> example [1, 2, 3, 0]
      • Methods for inserting and removing elements: append, extend, insert, pop, pop(index).

    Objectives

    • Chapter 5 Objectives (Part 1):

      • Construct lists and access items
      • Use methods to manipulate lists
      • Perform traversals of lists
      • Define simple functions that accept parameters and return values

    • Chapter 5 Objectives (Part 2):

      • Construct dictionaries and access entries
      • Use methods to manipulate dictionaries
      • Determine if a list or dictionary is the appropriate data structure

    Introduction

    • Lists and dictionaries are powerful ways to organize data in applications
    • Lists store data sequentially, while dictionaries store data by associating values.

    Dictionaries

    • Dictionaries organize information by association (like a dictionary itself!), not position.
    • Example: Looking up 'mammal' in a dictionary, you don't start at the first page, but go to the 'M' section.
    • In Python, a dictionary associates keys with values.
    • Key/value pairs are separated by commas and enclosed in curly braces {}.
    • A colon : separates the key from its value.
    • The key in a dictionary can be any immutable type. Example: {'Name': 'Molly', 'Age': 18} or {'Savannah': '476-3321', 'Nathaniel': '351-7743'}.

    Adding Keys and Replacing Values

    • Add new key/value pairs using [].
    • Example: info["name"] = "Sandy", info["occupation"] = "hacker".
    • Replace values using [] at an existing key. Example: info["occupation"] = "manager".

    Accessing Values

    • Use [] to access a value associated with a key. For example: info["name"].
    • If a requested key does not exist, an error will be raised.
    • Test for a key using the has_key method or the get method.

    Removing Keys

    • Remove a key/value pair with the pop() method. The pop() method can optionally take a default value if the key does not exist. Example:
      • print(info.pop("occupation")), info will then be {'name': 'Sandy'}.

    Traversing a Dictionary

    • Print all keys and their values using a for loop.
    • Example: for key in info: print(key, info[key]).
    • Another alternative is to iterate through the items. Example: for (key, value) in grades.items(): print(key, value)
    • Can sort the keys first and then iterate. Example: theKeys = list(info.keys()), theKeys.sort(), for key in theKeys: print(key, info[key]).

    Chapter Summary

    • Lists: Ordered collections. Mutable.
    • Tuples: Ordered collections. Immutable.
    • Functions: Organization of code
    • Dictionaries: Key-value pairs. Mutable.

    Additional Concepts

    • Mutability (Lists and Dictionaries are mutable)
    • Aliasing (two or more variables refer to the same list/object).
    • Return statement
    • Boolean functions
    • Main functions

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    Related Documents

    Python Fundamentals: Lists and Dictionaries PDF

    Description

    Explore the essentials of lists and dictionaries in Python through various examples and operations. This chapter covers list indices, mutability, and the use of functions like len and list. Test your understanding of these fundamental data structures with this quiz.

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