Data Structures

Question 1

“Type” command

Answer 1

Returns the class of the data, or the exact type if a Python object

Ex
Type(5)
Class ‘int’

Int, str, float

Question 2

Sequences

Answer 2

An ordered collection of values.

Sequence types:

Strings

Tuples

Lists

Question 3

Tuple

Answer 3

A tuple is an immutable sequence of 0 or more values.

Enclosed in round brackets and separated by commas.

Question 4

Tuple functions

Answer 4

X in tup. - True if x is an element in tup

Len(tup) - # of elements in tup

tup.count(x) - # of times element x occurs in tup

Tup.Index(x) - index location of first occ of x, returns ValueError exception if not in tup

Question 5

Lists

Answer 5

Lists are the same as tuples, but they are mutable- ie they can be changed.

Separated by commas, enclosed in square brackets.

Can use len, concatenate, indexing, slicing.

Question 6

List functions

Answer 6

Most are mutating functions, ie they modify the list.

Question 7

S.append (x)

Answer 7

Appends x to the end of s

Question 8

What does “pop” refer to?

Answer 8

The act of removing the last element of a list.

Question 9

What does “push “ refer to?

Answer 9

Adding an element to the same end of a list (like append)

Question 10

What does “stack “ refer to?

Answer 10

When push and pop are used on the same list.

Items are pushed onto the top of the stack, and then popped from the top of the stack.

Question 11

S.count(x)

Answer 11

Returns the number of times x appears in s

Question 12

S.extend(lst)

Answer 12

Appends each item of “lst” to s

Question 13

S.pop(i)

Answer 13

Removes and returns the item at index i in s

Question 14

S.index(x)

Answer 14

Returns the index value of the leftmost occurrence of x

Question 15

S.insert(i, x)

Answer 15

Inserts x before index location i (so that s[i] == x)

Question 16

S.remove(x)

Answer 16

Removes the leftmost occurrence of x in s

Question 17

S.reverse()

Answer 17

Reverses the order of the elements of s

Question 18

S.sort()

Answer 18

Sorts the elements of s into increasing order

Question 19

What is lexicographical ordering?

Answer 19

The order in which Python sorts a list of sequences. This is a general term meaning “alphabetical order “. It applies to any sequence of orderable values.

Question 20

List comprehensions

Answer 20

A special notation for creating lists

> > > [n * n for n in range(1, 11):

Creates list of squares from 1-10

Question 21

Filtered comprehensions

Answer 21

List comprehensions can filter out elements you don’t want.

> > > result = [n for n in nums if n > 0]
Returns only positive numbers

Question 22

What is a Python dictionary?

Answer 22

This is an extremely efficient data structure for storing pairs of values in the form key:value

Also referred to as associative arrays, maps, or hash tables.

> > > color = {‘red’ : 1, ‘blue’ : 2, ‘green’ : 3}

‘color’ is the dictionary name, has three members, one is ‘blue : 2’, where ‘blue’ is the key and ‘2’ is the associated value.

Question 23

Key restrictions

Answer 23

Keys have to be unique. You can’t have more than one key:value pair in the same dictionary.

Keys must be immutable, values can be mutable.

Question 24

Dictionary function

d.items()

Answer 24

Returns a view of the (key, value) pairs in d

Question 25

Dictionary function

d.keys()

Answer 25

Returns a view of the keys of d

Question 26

Dictionary function

d.values()

Answer 26

Returns a view of the values in d

Question 27

Dictionary function

d,get(key)

Answer 27

Returns the value associated with key

Question 28

Dictionary function

d.pop(key)

Answer 28

Removes key and returns its corresponding value

Question 29

Dictionary function

d.popitem()

Answer 29

Returns some (key, value) pair from d

Question 30

Dictionary function

d.clear()

Answer 30

Removes all items from d

Question 31

Dictionary function

d.copy()

Answer 31

Creates a copy of d

Question 32

Dictionary function

d.fromkeys(s, t)

Answer 32

Creates a new dictionary with keys taken from s and values taken from t

Question 33

Dictionary function

d.setdefault(key, v)

Answer 33

If key is in d, returns its value; if key is not in d, returns v and adds (key, v) to d

Question 34

Dictionary function

d.update(e)

Answer 34

Adds the (key, value) pairs in e to d