General Python

Question 1

Which library and what code is best to use when reading in csv files such as ‘train.csv’?

Answer 1

Question 2

If you have a pandas dataframe called data, how would you select the top 10 rows?

Answer 2

head = data[:10]

Question 3

For a pandas dataframe called data, how would you get the dimensions of the data set?

Answer 3

data.shape

Question 4

How do you find out the type of a variable ‘unknown_var’?

Answer 4

type(unknown_var)

Question 5

If

savings = 100 and result = savings * 1.1 ** 7

then does the following work? If not, what is the correct code?

print( “I started with $” + savings + “ and now have $” + result + “. Awesome!”)

Answer 5

No, the integers need to be converted to strings using str().

The correct code is:

print( “I started with $” + str(savings) + “ and now have $” + str(result) + “. Awesome!”)

Question 6

What do floats represent?

Answer 6

real numbers

Question 7

What does the int type represent?

Answer 7

integer numbers

Question 8

What does the str type represent?

Answer 8

strings

Question 9

What does the bool type represent?

Answer 9

True or False

Question 10

Give a 3 point summary about python lists

Answer 10

1. They name a collection of values
2. They contain any type
3. They can also contain different types

Question 11

What is the indexing of python lists?

Answer 11

Python lists are 0 indexed.

Question 12

For lists, how are the start and end included/excluded when list slicing?

For example, when taking a list, ‘first_10_primes’ and coding first_10_primes[3:5], what do we get?

Answer 12

You’d get the start number specified, but the end number is excluded.

For the example used, you’d only get the 4th and 5th element of the list and the 6th is excluded (remember that python lists are 0-indexed.

Question 13

What are the 3 main things that list manipulation allows you to do?

Answer 13

1. Change list elements
2. Add list elements
3. Remove list elements

Question 14

How do you delete an element from a list? Say the 3rd element.

Answer 14

del( my_list[2] )

Question 15

For a python list, x, if we run the code in the diagram, what is the outcome? Why?

Answer 15

The variable y does not contain each element in the list x but instead contains a reference/address to the list x.

Therefore, if we modify y, we modify x.

Question 16

How would you copy the elements of a list x into a list y?

Answer 16

You can’t simply use an equals sign as that will copy the reference/address to x.

You must use a list function or list slicing.

Question 17

What function gets the length of a list?

Answer 17

len( my_list )

Question 18

What are methods?

Answer 18

Functions that belong to objects.

Strings have methods.

floats have methods.

lists have methods.

Question 19

How do you get the index of a string “unknown” from a list my_list?

Answer 19

my_list.index( “unknown” )

Question 20

How do you count how many occurances of the integer 4 appear in the list my_list?

Answer 20

my_list.count( 4 )

Question 21

If we have the following code:

place = “poolhouse”

place_up = place.upper()

print(place)

print(place_upper)

is the variable place changed to be all upper case?

Answer 21

No. If place was a list, then place_up would be pointing to the same address as place and therefore, place would be changed to upper case. However, this is not the case for string objects.

Question 22

What are methods that add, remove and reverse elements in a python list?

Answer 22

list. append()
list. remove()
list. reverse()

Question 23

Complete this sentence:

“Numpy arrays can only contain…”

Answer 23

“one type.”