Python

Question 1

Εστω array A[3,5,7,8,9]. Ποιά η τιμή του A[-2]?

Answer 1

8

Question 2

for i in range(10)
is the same as:
for I in range(0,10,1)
?

Answer 2

Yes, default step is 1 and default start is 0. End (10) is non-inclusive

Question 3

For i in range(0,10,1) is the c equivalent
for(I=0; I<10; I++)
?

Answer 3

yes

Question 4

Result of this code?

x = 8

def foo():
    x = 5
    print(x)

foo()
print(x)

Answer 4

5
8

Question 5

Result of this code?

x = 8
def foo():
    global x
    x = 5
    print(x)

foo()
print(x)

Answer 5

5
5

Question 6

what is a package?

Answer 6

a package is a collection of modules which can me imported and used in other python scripts

Question 7

What’s tha value of __name__?

Answer 7

It depends:
If you run the script the value of __name__ is main.
If you don’t run it then it is the name of the script

Question 8

How to get the length of a list L?

Answer 8

len(L). len is a function that takes the list as an argument. L.list doesn’t work.

Question 9

What is a list in python?

Answer 9

Ordered (you can have indices)
Allows duplicates
Is mutable (changeable) e.g. L[2] = 8

Question 10

What is a set in python?

Answer 10

Unordered(no indices)
No duplicates
Immutable (you can only add or remove elements)
You can iterate with “in”

Question 11

What is a tuple

Answer 11

Ordered
Immutable
Less memory than list
Faster to loop -> the way to go in data science

Question 12

Are these two the same?

dict x = {"a":5, "b":6}
x.clear()

dict x = {"a":5, "b":6}
x = {}

Answer 12

No, clear empties the dictionary so all references are affected.
x = {} will create a new empty dictionary and assign it to x variable but the previous dictionary remains unaffected

Question 13

Difference between
open()
and
with open()

Answer 13

If you use open() you have to call close().
“with open()” doesn’t require the programmer to close the file. Its done automatically

Question 14

What is the JSON equivalent of a Python dict?

Answer 14

Object

Question 15

JSON equivalent of a python list?

Answer 15

Array

Question 16

JSON equivalent of a python tuple?

Answer 16

Array

Question 17

JSON equivalent of a python str?

Answer 17

String

Question 18

JSON equivalent of a python int, float?

Answer 18

Number

Question 19

JSON equivalent of python None?

Answer 19

null

Question 20

How are class methods defined?

Answer 20

A method without “self” as parameter is a class method that can be call like that:
Classname.method().

If an instance tries to call this method exception is raised.

if the method is declared like
@staticmethod
def foo(x) #no self param
…
then both class and instances can call this method.

Methods with self param are instance methods and can be called Object.method()

Question 21

What is a comprehension?

Answer 21

An elegant and more efficient way to create a new list from another list. Conditions may apply.

Question 22

What are generators?

Answer 22

Generator expressions can be used to create a new list from an iterable. They are memory efficient because they only calculate the next value when it is requested.

Question 23

Result of 14/8?

Answer 23

1.75

Question 24

Result of 14//8?

Answer 24

1

Question 25

What are the two types of casting?
Is there any data loss?

Answer 25

Implicit: Performed by python interpreter. No data loss
Explicit: Performed by us for example x = (int)1.75 –> x=1. Could have data loss.

Question 26

What are the types of supported comprehensions in python?

Answer 26

List, set and dictionary