Containers

Question 1

Concatenate two lists

Answer 1

li + other_li

Question 2

Remove 3’rd element of a list

Answer 2

del li[2]

Question 3

Remove 3rd and 4th element from a list

Answer 3

del a[2:4]

Question 4

Make a copy of a list

Answer 4

list.copy()
a[:]

Question 5

What will list2 = list do?

Answer 5

id(list) == id(list2) # => True

Both points to the same object

Question 6

Check for element 1 in list li

Answer 6

1 in li

Question 7

List:
- Add Single element
- Add multiple elements (from an iterable)
- Insert element x at index 1

Answer 7

list.append(x)
list.extend(iterable)
list.insert(1, x) # Insert x at index 1

Question 8

List:
- Remove first occurrence of x
- Remove the item at the given position / last in the list, and return it
- Remove all elements from a list

Answer 8

list.remove(x) # Remove first occurrence of x
list.pop([i]) # Remove the item at the given position / last in the list, and return it
list.clear()

Question 9

List: Search for element x, starting at 0, ending at index 5 inclusive

Answer 9

list.index(x, 0, 6)

Question 10

Find number of times x appears in the list.

Answer 10

list.count(x)

Question 11

List comprehension with filtering example

Answer 11

[x for x in [3, 4, 5, 6, 7] if x > 5]

Question 12

How to sort and reverse a list?

Answer 12

list.sort(key=None, reverse=False)
list.reverse()

Question 13

What are tuples?

Answer 13

Like lists but immutable

tup = (1, 2, 3)

Question 14

How to define tuple with single element?

Answer 14

type((1))    # => <class 'int'> !!!
type((1,))   # => <class 'tuple'> (add ,)

Question 15

How to define a dictionary?
- Empty
- With some values
- From a list

Answer 15

empty_dict = {}
filled_dict = {"one": 1, "two": 2, "three": 3}
dict_from_kv_pairs = dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])

Question 16

How to get an element from a dictionary? Both methods, how they differ

Answer 16

filled_dict["one"]
Throws Key Error when element not found

filled_dict.get("four")
Returns None when element not found

filled_dict.get("four", default)
Returns default when element not found

Question 17

Get list of keys and values from a dictionary

Answer 17

list(filled_dict.keys())    # => ["one", "two", "three"]
list(filled_dict.values())  # => [1, 2, 3]

Question 18

Check if one is a key in a dictionary

Answer 18

“one” in filled_dict

Question 19

How to update dictionary value under key “one”

Answer 19

filled_dict["one"] = 5

Question 20

How to delete dictionary value under key "one"

Answer 20

del filled_dict["one"]

Question 21

Dictionary comprehension where each value is a square of its key (for keys 2, 4, 6)

Answer 21

{x: x**2 for x in (2, 4, 6)}

Question 22

Define some set with initial values

Answer 22

some_set = {1, 1, 2, 2, 3, 4}

Question 23

Define an empty set

Answer 23

empty_set = set()

Question 24

Check if value is inside of a set

Answer 24

1 in some_set

Question 25

Insert value to a set

Answer 25

`filled_set.add(5)`

Question 26

What are some operations on sets in python?

Answer 26

``` filled_set & other_set # Intersection filled_set | other_set # Union {1, 2, 3, 4} - {2, 3, 5} # Difference => {1, 4} {1, 2, 3, 4} ^ {2, 3, 5} # Symmetric difference => {1, 4, 5} {1, 2} >= {1, 2, 3} # => False ```

Question 27

How to create a set comprehension?

Answer 27

`a = {x for x in 'abracadabra' if x not in 'abc'}`

Question 28

How to iterate a dictionary with a for loop?

Answer 28

``` for k, v in knights.items(): print(k, v) ```

Question 29

How to iterate a list (value + index) with a for loop?

Answer 29

``` for i, v in enumerate(['tic', 'tac', 'toe']): print(i, v) ```

Question 30

How to iterate two lists, one element at the time, simultaneously?

Answer 30

``` for q, a in zip(questions, answers): print('What is your {0}? It is {1}.'.format(q, a)) ```

Question 31

What does `list.index("foo")` return when element was not found?

Answer 31

`ValueError`

Question 32

Get value of key `five` of some dictionary. If it wasnt set yet, set it to 5 and return it.

Answer 32

`filled_dict.setdefault("five", 5)`

Question 33

Make a list where `[1, 2, 3]` is repeated 10 times

Answer 33

`[1, 2, 3] * 10`

Question 34

Get size of a list `s`

Answer 34

`len(s)`

Question 35

Get the smallest element of a list `s`

Answer 35

`min(s)`

Question 36

Get the largest element of a list `s`

Answer 36

`max(s)`

Question 37

Merge two dictionaries

Answer 37

`filled_dict.update({"four": 4})`

Question 38

Unpack dictionary `user_dict` as keyword arguments to a function (like `UserInDB(username, password)`)

Answer 38

`UserInDB(**user_dict)`

Question 39

Create read only set

Answer 39

`frozen_set = frozenset()`

Question 40

How to create double ended queue - What package to import - Add elements to beginning / end - Remove elements to beginning / end

Answer 40

``` from collections import deque d = deque('ghi') d.append('j') d.appendleft('f') d.pop() d.popleft() ```

Question 41

What is namedtuple, how to define and create it

Answer 41

`tuple` with named fields ``` from collections import namedtuple Point = namedtuple('Point', ['x', 'y']) p = Point(11, y=22) ```

Question 42

How to create heap - What package to import - Create heap from existing list - Add element to a heap - Get smallest element from a heap

Answer 42

``` from heapq import heapify, heappop, heappush data = [1, 3, 5, 7, 9, 2, 4, 6, 8, 0] heapify(data) # rearrange the list into heap order heappush(data, -5) # add a new entry [heappop(data) for i in range(3)] # fetch the three smallest entries ```

Question 43

How to create enum? - What package to import - Two methods of defining enum - How to use it

Answer 43

``` from enum import Enum // Class syntax class Color(Enum): RED = 1 GREEN = 2 BLUE = 3 // Functional syntax Color = Enum('Color', [('RED', 1), ('GREEN', 2), ('BLUE', 3)]) // Use Color.RED ```