DataCamp Python

Question 1

If you wanna use a package and you want to use it in your code what do you do?

Answer 1

first, import it at the beginning of your code

then if you want to use it write it with a dot at the end and then attach what you want to extract from the package

say you want to extract pi from the math package,

math.pi

Question 2

How do you bring add something to your script from package in a general way?

Answer 2

from math import pi

Question 3

Why is the NumPy array useful ?

Answer 3

You can perform calculations over entire arrays

Question 4

How can you simply a package name for use in your script

Answer 4

write as after your import

e.g. import numpy as np

Question 5

Whats the difference between when you add lists normally and when you add them using NumPy?

Answer 5

When you add them normally, it just combines the lists, one after the other.

With NumPy the lists will add

Question 6

What is one thing you can’t do with numpy arrays which you can do with regular arrays?

Answer 6

numpy arrays cannot contain arrays with different types.

If you try to build such a list, some of the elements’ types are changed to end up with a homogeneous list. This is known as type coercion.

Question 7

what package do you use to plot in python?

And how would you add it to your code?

Answer 7

import matplotlib.pyplot as plt

Question 8

How do you create a plot in python with matplotlib imported?

and how do you print it ?

Answer 8

plt. plot()
plt. show

(remember plt is a subset of matplot lib, you have to call it when doing operations)

Question 9

How do you convert an axis on a plot into log ?

Answer 9

plt.xscale(‘log’)

Question 10

what are the inputs of the histogram function?

Answer 10

hist(x, bins = ‘ ‘)

x is the list of values

bins refer to the list should be divided, if you don’t specify it will be 10 by default. Remember you need to write bins = ‘your value’.

Question 11

How to add labels to plots python?

Answer 11

plt.xlabel()

Question 12

How do you customise the range/length of the

Answer 12

plot. yticks()
plot. xticks()

Question 13

how would you customise the value of plt.yticks() shows?

Answer 13

You have an array after you ticks array to specify the value each tick should represent.

plt.yticks( [0,1,2,3,4], [‘0’,’1B’, ‘2B’, ‘3B’, ‘4B’, ‘5B’]

Question 14

how do you add text to a plot?

Answer 14

plt.text(1550, 71, ‘India’)

corresponding coordinates and name

Question 15

How do you create dictionaries?

Answer 15

use { }

Use a : to separate the key and the value.

call out a value using your_dict_name[key]

Question 16

How do you get all the keys from a dictionary?

Answer 16

europe.keys()

europe being your dictionary in this case.

Question 17

Why can you not use a list as a dictionary key?

Answer 17

because it isn’t an immutable object

it’s mutable - in other words it can be changed.

Question 18

When to use a dictionary and when to use a list?

Answer 18

Use a list when you have a collection of values were order matters and you want to be able to select entire subsets.

Use a dictionary when you want a table that allows you to lookup up values very easily and quickly using unique keys.

Question 19

How do you add a value in a dictionary?

Answer 19

europe[‘iceland’] = ‘reykjavik’

dict[key] = ‘what you want to set the key to’

Question 20

How do you create a table starting from dictionaries and using pandas?

Answer 20

create your dict, remember keys are the column labels and the values are the data for each column.

Question 21

what is csv short for ?

Answer 21

comma separated values.

Question 22

How can you read a csv file using panda

what do you really need to remember?

Answer 22

that the csv file name or directory needs to be written within qoutes.

Question 23

How can you change the index of csv file you are reading ?

Answer 23

cars = pd.read_csv(‘cars.csv’, index_col = 0 )

this sets the first column is used as the row labels

Question 24

What is the diff between loc and iloc

Answer 24

only difference is how you refer to columns and rows

iloc uses integers

Question 25

Why would you double brackets when indexing panda ?

Answer 25

not putting double brackets gives a series in terms of one column, even rows are converted into columns, which can be inconvenient.

Double brackets allow for a dataframe, and rows will remain rows.

Question 26

How to filter pandas dataframe?

Answer 26

Select your desired column(s) or row(s) and perform a operation, to filter, a comparison.

e.g. is_huge = brics[“area”] > 8

You need to store it in a variable so that you can index the dataframe, as follows:

brics[is_huge]

Question 27

in a for loop, what function do you have to use to get the index ?

Answer 27

enumerator

Question 28

what do you have to use to iterate a dictionary in a for loop?

What is this thing specified as?

Answer 28

for key, value in your_dict.items()

a method

Question 29

What do you have to use to iterate through all elements in a numpy array ?

What is this thing referred as ?

Answer 29

np.nditor(my_array)

function

Question 30

how do you iterate a panda dataframe in a for loop?

Answer 30

for lab, row in you_dataframe.iterrows()

Question 31

what is the efficient way of adding a column to a panda dataframe based of the data of another column?

Answer 31

your_dataframe[“new_column_name”] = your_dataframe[“selected_column”].apply(function)

Question 32

How do you create random numbers from numpy

Answer 32

np.random.rand()

Question 33

How to create random integer?

Answer 33

np.random.randint()

Question 34

How to set seed manually when creating random numbers?

Answer 34

np.random.seed(your_value)

Question 35

what sort of type does print() return ?

Answer 35

nonetype

Question 36

how to define functions in python?

Answer 36

def you

Question 37

Why is returning values generally more desirable than printing them out?

Answer 37

the type returned from printing is nonetype

Question 38

What is a tuple and what are its properties ?

Answer 38

essentially it is list that allows function to return multiple values

Like a list it can contain multiple values.

It is immutable - you can’t modify values !

constructed with parentheses

You can access values in a tuple in the same way you would with a list, by indexing.

Question 39

How do you use a tuple to return two values from a function?

Answer 39

define to output variables,

put them into a tuple

print the tuple

Question 40

How do you unpack a tuple?

Answer 40

a,b,c = your_tuple

unpacks to the elements of your tuple into the varibles a,b,c

Question 41

Why would equate a function to more than one variable?

Answer 41

If the function returns more than variable maybe you want to print them individually and not in bracket form after each other

Question 42

Explain this code.

Answer 42

dataframe saved in df variable

There is empty dictionary defined as langs_count

the ‘lang’ column is saved as col

The for loop goes through every value in the col

For each value we test whether the value is in the dictionary if it is, add one to the value the to the associated key, else update the dictionary and add the entry and add one to its value.

Question 43

How do you add something to a dictionary?

Answer 43

your_dict.update({key : value})

Question 44

How to change a key value in a dictionary?

Answer 44

your_dict[key] = value

Question 45

How do you make a variable global when it is in a local environment ?

Answer 45

write

global your_variable

Question 46

If you change a variable in a function what sort of scope is it?

Answer 46

local scope.

Question 47

How does python go through finding variables in nested functions?

Answer 47

First it looks locally in the nested function

If it does not find the variable, it goes to the function the previous function is nested in and searches locally there.

If it still can’t find it, it searches globally.

Question 48

How do you change a variable in nested function (all the functions) without changing it globally?

Answer 48

use

nonlocal

Question 49

Why are nested functions necessary?

Answer 49

They are necessary to scale programs, if there is code that needs to be repeated multiple times in a function, it is better to write a function to replace that code.

Question 50

How would you use nested functions to concatenate three input words ?

Answer 50

Question 51

How are the scopes searched?

Answer 51

Local Scope

Enclosing Functions

Global

Built-in

Question 52

How does this code work?

Answer 52

The outer function determines the number of copies

The inner function takes in a word and multiplies it by n, the value is then returned to outer

A value for n is assigned to twice and thrice

Both Twice and Thrice are input ‘hello’ and the print function is called on them.

With a value of n associated with Twice and Thrice, the inner function returns to the concatenated strings which are then princted.

Question 53

What are default arguments in a function?

Answer 53

Default argument is a variable already defined in the function

in the case that the user does not personally define the variable, the default value is used.

This can be useful when a value for the variable is required.

Question 54

What are flexible arguments and how are they defined?

Answer 54

Flexible arguments allow for any number of inputs from the user.

It is defined within the function brackets with a * in front of the variable

e.g. *args

Question 55

what do **kwargs do ?

Answer 55

they allow for an arbitrary amount of key,value pairs defined by the user.

you can define any kwarg by placing a ** in front.

Question 56

when you have used **kwargs how do you loop through the values ?

Answer 56

for key, value in kwargs.items():

Question 57

what do lambda functions allow?

Answer 57

Allow you to write functions quick

Question 58

What does the map() function do ?

Answer 58

The map() function applies a given function to each item of an iterable (list, tuple etc.) and returns a list of the results.

Question 59

a function that allows you to remove elements from a list that don’t match your criteria

Answer 59

filter()