Chapter 5 Flashcards
List
-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)
Dictionary
-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
Each item in a list has a unique ___ that specifies its position (from____)
-index
-0 to length -1
Is a list mutable or immutable?
mutable
-elements can be inserted, removed, or replaced
A list maintains its ___ but its ___ (its length and contents) can change
-identity
-state
How can a subscript operator be used in a list?
-To replace an element
ie. example[3] = 0
Here “0” replaces the element in position 3 of the list called example
How would you replace each number in a list with its square?
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]
What method can be used to extract a list of the words in a sentence?
string method split
ie.
IN: sentence = “This example has five words.”
IN: words = sentence.split()
IN: words
OUT: [‘This’, ‘example’, ‘has’, ‘five’, ‘words.’]
How would you convert a list of words to uppercase?
IN: for index in range(len(words)):
words[index] = words[index].upper()
L.append(element)
adds element to the end of L.
L.extend(aList)
Adds the elements of aList to the end of L.
L.insert(index, element)
Inserts element at index if index is less than the length of L. Otherwise, inserts element at the end of L.
L.pop()
Removes and returns the element at the end of L.
L.pop(index)
Removes and returns the element at index
in…
determines an element’s presence or absence, but does not return position of element (if found)
What method that is used with strings can’t be used to locate an element’s position in a list?
the find method
If we can’t use the find method how can we search a list?
-use method index to locate an element’s position in a list.
Since method index raises an exception when the target element is not found how can we guard against this?
-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)
natural ordering
the placement of data items relative to each other by some internal criteria, such as numeric value or alphabetical value.
A list’s elements are always ordered by ____ but you can impose a ____ on them
-position
-natural ordering
T or F: When the elements can by related by comparing them <, >, and == they cannot be sorted
F: When the elements can by related by comparing them <, >, and == they can be sorted
Method sort
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]
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?
mutator methods (e.g., insert, append, extend, pop, and sort)
Since mutator methods usually return no value of interest to caller what special value does Python automatically return?
-None
ie:
IN: aList = aList.sort()
IN: print(aList)
OUT: None
Aliases
2 variables refer to the same list object
ie:
first = [10, 20, 30]
second = first
How can you prevent aliasing?
Create a new object and copy contents of original
ie:
third = []
for element in first:
third.append(element)
== operator
-use to see whether 2 variables refer to the exact same object or to different
Object Identity
when the == operator returns True if the variables are aliases for the same object
Structural Equivalence
Unfortunately, when the == operator returns True if the contents of 2 diff objects are the same
Tuple
-Resembles a list but is immutable
-indicated by enclosing elements in ()
ie:
fruits = (“apple”, “banana”)
Syntax of simple function definitions
-consists of a header and body
-syntax:
def <function>(<parameter-1>, ..., <parameter-n>):</parameter-n></parameter-1></function>
<body>
</body>
parameter and arguments
-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
Return statement
-place at each exit pint of a function when function should explicitly return a value
-syntax:
return <expression></expression>
what happens if a function contains no return statement?
Python transfers control to the caller after the last statement in the function’s body is executed
-the special value None is automatically returned
Boolean functions
-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
main function
-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
Dictionaries
-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
Dictionary Literals
-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: {}
dictionary pairs are sometimes called___
entries
T or F: Keys in a dictionary can be data of any mutable types
F: Keys in a dictionary can be data of any immutable types, including other data
structures
-they are normally strings and integers
How do you add a new key/value pair to a dictionary?
-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>
What do you use to replace a value at an existing dictionary key?
[]
ie:
IN: info[“occupation”] = “manager”
IN: info
OUT: {‘name’:‘Sandy’, ‘occupation’: ‘manager’}
Dictionaries- how would you obtain a value associated with a key
-Use []
ie:
IN: info[“name”]
OUT: ‘Sandy’
-if key is not present an error is raised
Dictionaries- if the existence of a key is uncertain, test for it using the method____ or _____
- has_key
- get
ie:
if “job” in info:
print(info.[“job”])
To delete an entry from a dictionary, remove using the method___
- pop
- it expects a key and optional default value as args
ie:
IN: print(info.pop(“job”, None))
OUT: None
using for loop with dictionary
- 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])
What is dictionary method items?
- 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’)]
Entries are represented as ____ within the list
- tuples
for (key, value) in grades.items():
print(key, value)
___ the list first then traverse it to print the entries of the dictionary in alphabetical order.
- sort
theKeys = list(info.keys())
theKeys.sort()
for key in theKeys:
print(key, info[key])
