Chapter 5

Question 1

List

Answer 1

-Sequence of data values (items or elements)
-Allows programmer to manipulate a sequence of data values of any types
-Examples: to-do list, shopping list, text document (list of lines)

Question 2

Dictionary

Answer 2

-Organizes data values by association with other data values rather than by sequential position
-In Python, associates a set of keys with values
-example: the keys in Webster’s dictionary comprise the set of words while the associated data values are their definitions.
-other examples: phone books, address books, encyclopedias etc

Question 3

Each item in a list has a unique ___ that specifies its position (from____)

Answer 3

-index
-0 to length -1

Question 4

Is a list mutable or immutable?

Answer 4

mutable
-elements can be inserted, removed, or replaced

Question 5

A list maintains its ___ but its ___ (its length and contents) can change

Answer 5

-identity
-state

Question 6

How can a subscript operator be used in a list?

Answer 6

-To replace an element
ie. example[3] = 0
Here “0” replaces the element in position 3 of the list called example

Question 7

How would you replace each number in a list with its square?

Answer 7

IN: numbers = [2, 3, 4, 5]
IN: for index in range(len(numbers)):
numbers[index] = numbers[index] **2
IN: numbers
OUT: [4, 9, 16, 25]

Question 8

What method can be used to extract a list of the words in a sentence?

Answer 8

string method split
ie.
IN: sentence = “This example has five words.”
IN: words = sentence.split()
IN: words
OUT: [‘This’, ‘example’, ‘has’, ‘five’, ‘words.’]

Question 9

How would you convert a list of words to uppercase?

Answer 9

IN: for index in range(len(words)):
words[index] = words[index].upper()

Question 10

L.append(element)

Answer 10

adds element to the end of L.

Question 11

L.extend(aList)

Answer 11

Adds the elements of aList to the end of L.

Question 12

L.insert(index, element)

Answer 12

Inserts element at index if index is less than the length of L. Otherwise, inserts element at the end of L.

Question 13

L.pop()

Answer 13

Removes and returns the element at the end of L.

Question 14

L.pop(index)

Answer 14

Removes and returns the element at index

Question 15

in…

Answer 15

determines an element’s presence or absence, but does not return position of element (if found)

Question 16

What method that is used with strings can’t be used to locate an element’s position in a list?

Answer 16

the find method

Question 17

If we can’t use the find method how can we search a list?

Answer 17

-use method index to locate an element’s position in a list.

Question 18

Since method index raises an exception when the target element is not found how can we guard against this?

Answer 18

-First, use the in operator to test for presence
-then the index method if this test returns True.
ie.
aList = [34, 45, 67]
target = 45
if target in aList:
print(aList.index(target))
else:
print(-1)

Question 19

natural ordering

Answer 19

the placement of data items relative to each other by some internal criteria, such as numeric value or alphabetical value.

Question 20

A list’s elements are always ordered by ____ but you can impose a ____ on them

Answer 20

-position
-natural ordering

Question 21

T or F: When the elements can by related by comparing them <, >, and == they cannot be sorted

Answer 21

F: When the elements can by related by comparing them <, >, and == they can be sorted

Question 22

Method sort

Answer 22

mutates a list by arranging its elements in ascending order
ie.
IN: l = [4, 2, 10, 8]
IN: l.sort()
IN: l
OUT: [2, 4, 8, 10]

Question 23

All functions and methods from previous chapters return a value that the caller can then use to complete its work. What kind of methods usually return no value of interest to caller?

Answer 23

mutator methods (e.g., insert, append, extend, pop, and sort)

Question 24

Since mutator methods usually return no value of interest to caller what special value does Python automatically return?

Answer 24

-None
ie:
IN: aList = aList.sort()
IN: print(aList)
OUT: None

Question 25

Aliases

Answer 25

2 variables refer to the same list object
ie:
first = [10, 20, 30]
second = first

Question 26

How can you prevent aliasing?

Answer 26

Create a new object and copy contents of original
ie:
third = []
for element in first:
third.append(element)

Question 27

== operator

Answer 27

-use to see whether 2 variables refer to the exact same object or to different

Question 28

Object Identity

Answer 28

when the == operator returns True if the variables are aliases for the same object

Question 29

Structural Equivalence

Answer 29

Unfortunately, when the == operator returns True if the contents of 2 diff objects are the same

Question 30

Tuple

Answer 30

-Resembles a list but is immutable
-indicated by enclosing elements in ()
ie:
fruits = (“apple”, “banana”)

Question 31

Syntax of simple function definitions

Answer 31

-consists of a header and body
-syntax:
def <function>(<parameter-1>, ..., <parameter-n>):</parameter-n></parameter-1></function>

<body>
</body>

Question 32

parameter and arguments

Answer 32

-name used in function definition for an argument that is passed to the function when it is called
-The number & position of arguments of a function call should match the # & positions of the parameters in the definition
-some functions expect no arguments - defined with no parameters

Question 33

Return statement

Answer 33

-place at each exit pint of a function when function should explicitly return a value
-syntax:
return <expression></expression>

Question 34

what happens if a function contains no return statement?

Answer 34

Python transfers control to the caller after the last statement in the function’s body is executed
-the special value None is automatically returned

Question 35

Boolean functions

Answer 35

-Usually tests its argument for the presence or absence of some property
-returns True if property is present; False otherwise
ie:
IN: odd(5)
OUT: True

Question 36

main function

Answer 36

-serves as entry point for a script
-usually expects no arguments and returns no value
-definition of main & other functions can appear in no particular order in the script as long as main is called at the end of the script
-script can be run from IDLE, imported into the shell, or run from a terminal command prompt

Question 37

Dictionaries

Answer 37

-Organizes info by association, not position
-data structures organized by assoc are also called tables and association lists
-in Python, a dictionary assoc a set of keys with data values

Question 38

Dictionary Literals

Answer 38

-written as a sequence of key/value pairs separated by commas
-enclosed in curly brackets ({ and})
-a colon (:) separates a key and value
-ie:
{‘Savannah’:‘476‐3321’, ‘Nathaniel’:‘351‐7743’}
an empty dictionary: {}

Question 39

dictionary pairs are sometimes called___

Answer 39

entries

Question 40

T or F: Keys in a dictionary can be data of any mutable types

Answer 40

F: Keys in a dictionary can be data of any immutable types, including other data
structures
-they are normally strings and integers

Question 41

How do you add a new key/value pair to a dictionary?

Answer 41

-use []
<a>[<a>] = <a>
-ie:
IN: info = {}
IN: info[“name”] = “Sandy”
IN: info[“occupation”] = “hacker”
IN: info
OUT: {‘name’:‘Sandy’, ‘occupation’:‘hacker’}</a></a></a>

Question 42

What do you use to replace a value at an existing dictionary key?

Answer 42

[]
ie:
IN: info[“occupation”] = “manager”
IN: info
OUT: {‘name’:‘Sandy’, ‘occupation’: ‘manager’}

Question 43

Dictionaries- how would you obtain a value associated with a key

Answer 43

-Use []
ie:
IN: info[“name”]
OUT: ‘Sandy’
-if key is not present an error is raised

Question 44

Dictionaries- if the existence of a key is uncertain, test for it using the method____ or _____

Answer 44

• has_key
• get
  ie:
  if “job” in info:
  print(info.[“job”])

Question 45

To delete an entry from a dictionary, remove using the method___

Answer 45

• pop
• it expects a key and optional default value as args
  ie:
  IN: print(info.pop(“job”, None))
  OUT: None

Question 46

using for loop with dictionary

Answer 46

• the loop’s variable is bound to each key in an unspecified order
• to print all of the keys and their values:
  for key in d:
  print(key, d[key])

Question 47

What is dictionary method items?

Answer 47

• returns a list of tuples containing the keys & values for each entry
• list(d.items())
• ie:
  IN: grades = {90:‘A’, 80:‘B’, 70:‘C’}
  IN: list(grades.items())
  OUT: [(80, ‘B’), (90,‘A’), (70,‘C’)]

Question 48

Entries are represented as ____ within the list

Answer 48

• tuples
  for (key, value) in grades.items():
  print(key, value)

Question 49

___ the list first then traverse it to print the entries of the dictionary in alphabetical order.

Answer 49

• sort
  theKeys = list(info.keys())
  theKeys.sort()
  for key in theKeys:
  print(key, info[key])