Chapter 5 - data structures Flashcards
how to slice?
x[1:3] returns the substring from index 1 to index 2 (does not include 3rd)
what does this return?
myword = ‘help’
myword[-2:-1]
‘l’
what does this return?
w = ‘mannn’
print(myword[:2])
print(myword[2:])
ma
nnn
what happens?
w = ‘mann’
print([myword[:])
prints entire string
mann
x = “myy wordssss”
x[4:3]
what does this return?
’’
^empty string
what does this return?
x = “myy wordssss”
x[::2]
‘mywrss’
^skips every other index, due to jump of 2 in substring
what does this return?
x = “myy wordssss”
x[::-2]
‘ssdo y’
^indexes backwards in steps of 2
how to reverse real easy using step function?
x[::-1]
how would you concatenate a string to itself 3 times?
x*=3
create an empty list
ok = []
how to delete list elements w/o using del keyword?
set part of list x[0:2] = []
add 25 to the end of this list:
a = [1, 2, 4, 3, 2]
a += [25]
^can only add lists together, which is why 25 is in brackets
bob = “123456789”
bob[0:-1]
returns?
‘12345678’
what will this return:
numlist = [1, 2, 3, 4, 5, 6]
numlist[-1] = []
[1, 2, 3, 4, 5, []]
you need the colon operator to actually replace! (numlist-[-1:] = [])
what is the only way to index backwards using the [:]?
use negative steps, such as:
x[::-1]
what will the following return:
- iter(range(4))
- iter([1, 2, ‘4’, 8])
- iter(33)
<range_iterator at 0x7fb888bb480f0>
2.
<list_iterator at (stuff im too lazy to write)>
- TypeError: ‘int’ object is not iterably
what does range create?
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
what will this return?
l = [1, 2, 3, 4, 5, 6]
l[::-1]
[6, 5, 4, 3, 2, 1]
true/false:
enumerate requires both an index and item iterator to be “used to its full potential”
false, if given only one iterator variable in a for loop will just set equal to a tuple (index, item)
tuple vs. list
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
how to create tuple with one entry
oneTup = (7,)
prints out (7,)
im told parentheses and comma are necessary, not sure abt the parentheses part bcz it worked :(
what type is returned if you index a tuple?
returns a tuple mytup = (3, 7, “m”, 20)
mytup[2:3]
returns (“m”,)
can a tuple be typecasted?
yes, to a list. also, can typecast lists and strings to tuples
packing vs. unpacking
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!
what will this return:
oneTup = “hello”
a, b, c = oneTup
print(a, b, c)
error, too many values to unpack!
what does this return:
list(range(12,3,-2))
[12, 10, 8, 6, 4]
Create the sequence [3, 2, 1].
list(range(3, 0, -1))
what will this print:
list(range(2, 4, 5))
[2]
what will this print:
empTup = (,)
len(empTup)
error, cannot have just a comma in a tuple
myTuple = (1,2,3)
myTuple[0]
returns 1
difference between +=, append, and extend for adding tuples?
+= and extend only add the values to the end, whereas append adds the actual tuple
what does this return?
mytup = 7, 3, 5, 6
enumerate(mytup)
<enumerate at 0x78c7018b9d40>
basically nothing, but also not an error
what is vectorizing code?
making code more succinct by using in-built functions BOY
true/false:
The range function returns a list
False, returns an iterable of type range
Tuples are a mutable data type
true/false
false
what would the result be:
[c+’!’ for c in “Yay”]
[‘Y!’, ‘a!’, ‘y!’]
list comprehensions create, well, a list!
thus can be mutated where a string could not
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]]
flatlist = [j for i in nestedlist for j in i]
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
numlist = [1, 2, 3, 55, 6, 7, 8, 10]
listsum = [sum(numlist[:i]) for i in range(1, len(numlist)+1)]
print(listsum)
list comprehension format
[ (output function set to each element of list) for (iterator) in (iterable) if _______]
MIGHT HAVE IF and/or ELSE MIGHT NOT
what will the following return:
numlist = [2, 33, -5, 11, 4]
numlist.insert(3, 33)
numlist
[2, 33, -5, 33, 11, 4]
rmr, insert does not replace, it just adds!
numlist = [2, 33, -5, 11, 4]
numlist.pop()
numlist
[2, 33, -5, 11, 4]
removes at index = -1, defaul pop() is pop(-1)
imr = range(6)
next(imr)
vs.
imr = iter(range(6))
next(imr)
i have absolutely no idea
