Chapter 5 - data structures

Question 1

how to slice?

Answer 1

x[1:3] returns the substring from index 1 to index 2 (does not include 3rd)

Question 2

what does this return?

myword = ‘help’
myword[-2:-1]

Answer 2

‘l’

Question 3

what does this return?

w = ‘mannn’
print(myword[:2])
print(myword[2:])

Answer 3

ma
nnn

Question 4

what happens?

w = ‘mann’
print([myword[:])

Answer 4

prints entire string

mann

Question 5

x = “myy wordssss”
x[4:3]

what does this return?

Answer 5

’’
^empty string

Question 6

what does this return?

x = “myy wordssss”
x[::2]

Answer 6

‘mywrss’

^skips every other index, due to jump of 2 in substring

Question 7

what does this return?
x = “myy wordssss”
x[::-2]

Answer 7

‘ssdo y’

^indexes backwards in steps of 2

Question 8

how to reverse real easy using step function?

Answer 8

x[::-1]

Question 9

how would you concatenate a string to itself 3 times?

Answer 9

x*=3

Question 10

create an empty list

Answer 10

ok = []

Question 11

how to delete list elements w/o using del keyword?

Answer 11

set part of list x[0:2] = []

Question 12

add 25 to the end of this list:
a = [1, 2, 4, 3, 2]

Answer 12

a += [25]

^can only add lists together, which is why 25 is in brackets

Question 13

bob = “123456789”
bob[0:-1]

returns?

Answer 13

‘12345678’

Question 14

what will this return:

numlist = [1, 2, 3, 4, 5, 6]
numlist[-1] = []

Answer 14

[1, 2, 3, 4, 5, []]

you need the colon operator to actually replace! (numlist-[-1:] = [])

Question 15

what is the only way to index backwards using the [:]?

Answer 15

use negative steps, such as:

x[::-1]

Question 16

what will the following return:

1. iter(range(4))
2. iter([1, 2, ‘4’, 8])
3. iter(33)

Answer 16

<range_iterator at 0x7fb888bb480f0>
2.
<list_iterator at (stuff im too lazy to write)>

3. TypeError: ‘int’ object is not iterably

Question 17

what does range create?

Answer 17

creates an iterator of type range (though can be casted to list) ONE AT A TIME until
n-1 value of range(n) is reached

Question 18

what will this return?

l = [1, 2, 3, 4, 5, 6]
l[::-1]

Answer 18

[6, 5, 4, 3, 2, 1]

Question 19

true/false:
enumerate requires both an index and item iterator to be “used to its full potential”

Answer 19

false, if given only one iterator variable in a for loop will just set equal to a tuple (index, item)

Question 20

tuple vs. list

Answer 20

tuples are IMMUTABLE, and are put in parentheses instead of colons OR just plain text like:
tuple1 = 1, 3

slicing, indexing, concatenation, and len methods are the same

Question 21

how to create tuple with one entry

Answer 21

oneTup = (7,)
prints out (7,)

im told parentheses and comma are necessary, not sure abt the parentheses part bcz it worked :(

Question 22

what type is returned if you index a tuple?

Answer 22

returns a tuple mytup = (3, 7, “m”, 20)
mytup[2:3]
returns (“m”,)

Question 23

can a tuple be typecasted?

Answer 23

yes, to a list. also, can typecast lists and strings to tuples

Question 24

packing vs. unpacking

Answer 24

packing = puts multiple values separated by commas into tuple

unpacking = setting equal amount of variables to left side of tuple so each gets assigned tuple elements in that order

unpacking ispossible for lists and strings too!

Question 25

what will this return:
oneTup = “hello”
a, b, c = oneTup
print(a, b, c)

Answer 25

error, too many values to unpack!

Question 26

what does this return:
list(range(12,3,-2))

Answer 26

[12, 10, 8, 6, 4]

Question 27

Create the sequence [3, 2, 1].

Answer 27

list(range(3, 0, -1))

Question 28

what will this print:
list(range(2, 4, 5))

Answer 28

[2]

Question 29

what will this print:
empTup = (,)
len(empTup)

Answer 29

error, cannot have just a comma in a tuple

Question 30

myTuple = (1,2,3)
myTuple[0]

Answer 30

returns 1

Question 31

difference between +=, append, and extend for adding tuples?

Answer 31

+= and extend only add the values to the end, whereas append adds the actual tuple

Question 32

what does this return?
mytup = 7, 3, 5, 6
enumerate(mytup)

Answer 32

<enumerate at 0x78c7018b9d40>
basically nothing, but also not an error

Question 33

what is vectorizing code?

Answer 33

making code more succinct by using in-built functions BOY

Question 34

true/false:
The range function returns a list

Answer 34

False, returns an iterable of type range

Question 35

Tuples are a mutable data type

true/false

Answer 35

false

Question 36

what would the result be:
[c+’!’ for c in “Yay”]

Answer 36

[‘Y!’, ‘a!’, ‘y!’]
list comprehensions create, well, a list!
thus can be mutated where a string could not

Question 37

lab 13 Problem 6: Flatten a nested list using a list comprehension. For example, [[1,2], [3,4]] would become [1,2,3,4].
nestedlist = [[1, 2], [3, 4, 5], [9, 7]]

Answer 37

flatlist = [j for i in nestedlist for j in i]

Question 38

lab 13 Problem 7: Create a list of numbers. From the original list, create a list of the running sums of the numbers. Do this using a list comprehension

Answer 38

numlist = [1, 2, 3, 55, 6, 7, 8, 10]
listsum = [sum(numlist[:i]) for i in range(1, len(numlist)+1)]
print(listsum)

Question 39

list comprehension format

Answer 39

[ (output function set to each element of list) for (iterator) in (iterable) if _______]

MIGHT HAVE IF and/or ELSE MIGHT NOT

Question 40

what will the following return:

numlist = [2, 33, -5, 11, 4]
numlist.insert(3, 33)
numlist

Answer 40

[2, 33, -5, 33, 11, 4]

rmr, insert does not replace, it just adds!

Question 41

numlist = [2, 33, -5, 11, 4]
numlist.pop()
numlist

Answer 41

[2, 33, -5, 11, 4]
removes at index = -1, defaul pop() is pop(-1)

Question 42

imr = range(6)
next(imr)

vs.

imr = iter(range(6))
next(imr)

Answer 42

i have absolutely no idea