# 2 Introduction to Python (II) Flashcards

## Matplotlib, dictionaries, dataframes... https://colab.research.google.com/drive/1fKMFrRbIJQE8Tpa06us0qQPnamBn957z?usp=sharing

1 What is Matplotlib?

A plotting library for the Python programming language and its numerical mathematics extension NumPy. It provides an object-oriented API for embedding plots into applications using general-purpose GUI

2 Complete code:

import matplot… as …

import matplotlib.pyplot as plt

3 Make a line plot (year x-axis, pop y-axis)

year=[‘1975’,’1976’,’1977’]

pop=[2340,2405,2890]

import matplotlib.pyplot as plt

plt. plot(year,pop)

plt. show()

4 How to display a matplotlib plot?

plt.show()

5 Print the last item of the list year:

year=[‘1975’,’1976’,’1977’]

print(year[-1])

print(year[2])

6 What is a scatter plot?

A type of plot or mathematical diagram using Cartesian coordinates to display values for typically two variables for a set of data

7 Complete code (scatter plot):

x = [1,3,5] y= [2,6,7]

’'’import mat….

…

plt.show()’’’

import matplotlib.pyplot as plt

plt. scatter(x,y)

plt. show()

8 Change the line plot below to a scatter plot

year=[‘1975’,’1976’,’1977’]

pop=[2340,2405,2890]

import matplotlib.pyplot as plt

plt. plot(year,pop)

plt. show()

plt. scatter(year,pop)

plt. show()

9 Put the x-axis on a logarithmic scale

day=[‘1’,’2’,’3’]

virus=[18,55,320]

import matplotlib.pyplot as plt

plt. scatter(day,virus)

plt. show()

plt. scatter(day,virus)

plt. xscale(‘log’)

plt. show()

10 What is a correlation coefficient?

A value that indicates the strength of the relationship between variables. The coefficient can take any values from -1 to 1.

11 What is a histogram?

An approximate representation of the distribution of numerical or categorical data

12 Create histogram

years = [1975,1976,1978,1975]

import matplotlib.pyplot as plt

plt. hist(years)

plt. show()

13 Create histogram with 5 bins using data (list)

data = [random.randint(1, 5) for _ in range(100)]

plt.hist(data,bins=5)

14 What is the use of plt.clf() ?

Cleans a plot up again so you can start afresh

15 You want to visually assess if the grades on your exam follow a particular distribution. Which plot do you use?

Histogram

16 You want to visually assess if longer answers on exam questions lead to higher grades. Which plot do you use?

Scatter plot

17 Add labels

year =list(range(1975,2000))

scores = list(range(1,26))

plt.scatter(year,scores)

…

plt. xlabel(‘year’)

plt. ylabel(‘scores’)

plt. show()

18 Add ‘scores’ as a title

data = [int(random.randint(1, 5)) for _ in range(100)]

plt.hist(data,bins=5)

…

plt.plot()

plt.title(‘years’)

19 Add log scale

year =list(range(1975,2000))

scores= [2**n for n in range(25)]

plt.scatter(year,scores)

…

plt. yscale(‘log’)

plt. show()

20 What are ticks in matplotlib?

Ticks are the values used to show specific points on the coordinate axis. It can be a number or a string.

21 What is a legend in matplotlib?

The legend of a graph reflects the data displayed in the graph’s Y-axis

22 Change the ticks in the x-axis to strings

x=[1, 3, 5]

y=[1, 5, 9]

import matplotlib.pyplot as plt

plt.scatter(x,y)

plt. xticks(x, [“one”,”three”,”five”])

plt. show()

23 Write a scatter plot with gdp as independent variable and population size as the size argument

gdp=[100, 200, 300]

life_exp=[50, 70, 82]

pop_size=[30,20,40]

import matplotlib.pyplot as plt

plt. scatter(gdp, life_exp, s =pop_size)

plt. show()

24 What is a dependent variable?

A variable (often denoted by y ) whose value depends on that of another.

25 What is an independent variable?

A variable (often denoted by x ) whose variation does not depend on that of another.

26 Code: Scatter plot with text ‘A’ pointing at the second element

gdp=[100, 200, 300]

life_exp=[50, 70, 82]

import matplotlib.pyplot as plt

plt. scatter(gdp, life_exp)

plt. text(195,65,’A’)

plt. show()

27 Add a grid to a matplot figure

plt.grid(True)

28 Get the position of germany

countries = [‘spain’, ‘france’, ‘germany’, ‘norway’]

countries.index(‘germany’)

29 What is the difference between list and dictionary in Python?

A list is an ordered sequence of objects, whereas dictionaries are unordered sets. But the main difference is that items in dictionaries are accessed via keys and not via their position.

30 Get the keys

europe = {‘spain’:’madrid’, ‘france’:’paris’, ‘germany’:’berlin’, ‘norway’:’oslo’ }

Outcome:

dict_keys([‘spain’, ‘france’, ‘germany’, ‘norway’])

print(europe.keys())

31 Get the capital of norway

europe = {‘spain’:’madrid’, ‘france’:’paris’, ‘germany’:’berlin’, ‘norway’:’oslo’ }

Outcome: oslo

print(europe[‘norway’])

32 Add italy and rome to the dictionary

europe = {‘spain’:’madrid’, ‘france’:’paris’,

‘germany’:’berlin’ }

europe[‘italy’]=’rome’

33 Check whether the dictionary has spain

europe = {‘spain’:’madrid’, ‘france’:’paris’,

‘germany’:’berlin’ }

print(‘spain’ in europe)

34 Outcome of:

europe = {‘spain’:’madrid’, ‘france’:’paris’, ‘germany’:’berlin’, ‘norway’:’oslo’ }

print(‘madrid’ in europe)

FALSE

35 Delete spain

europe = {‘spain’:’madrid’, ‘france’:’paris’,

‘norway’:’oslo’}

del(europe[‘spain’])

36 Update the capital of spain with madrid

europe = {‘spain’:’Barcelona’, ‘france’:’paris’,

‘norway’:’oslo’}

europe[‘spain’]=’madrid’