How would I plot points and make a line in python?

Question

So Im supposed to plot graphs. Make a function plot_line(p1,p2) that takes two points as input arguments and plots the line between them. The two input arguments should be lists or tuples specifying x- and y-coordinates, i.e., p1 =(x1,y1)

I tried with this but my graph is just empty in the plot table. Nothing comes up

import matplotlib.pyplot as plt
    
print('this code will plot two points in a graph and make a line')

x1 = (float(input('enter first x value: ')))
y1 = (float(input('enter first y value: ')))
x2 = (float(input('enter second x value: ')))
y2 = (float(input('enter second y value: ')))


def plotline(p1,p2):
    p1=[x1,y1]
    p2=[x2,y2]
    
    return p1,p2


x=plotline(x1,x2)
y=plotline(x1,x2)

plt.plot(x,y, label='x,y')

plt.xlabel('x')
plt.ylabel('y')
plt.legend()
plt.axis([-10,10,-10,10])
plt.title('two lines')
plt.show()

Hi, i just run your code and get a nice line. Can you elaborate on your situation further? — bench
– bench, Commented Oct 4, 2020 at 15:22
im supposed to get one vertical and one horizontal line by doing x=0 and y=0 in the other, but it doesnt work. — Vro
– Vro, Commented Oct 4, 2020 at 15:49

Prateek Tripathi · Accepted Answer · 2020-10-04 15:35:30Z

1

plt.plot() takes three input to work

If you just write plt.plot(3,4), it only pins the location but doesn't point it.

You need to write plt.plot(3,4,'o'). this way you will pin and point the location with a 'o' structure

answered Oct 4, 2020 at 15:35

Prateek Tripathi

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2 Comments

Vro Over a year ago

what are you talking about?? no

luca76 Over a year ago

Please be more precise. Describe the programming language you are using

bench · Accepted Answer · 2020-10-04 16:05:18Z

1

Complementing Prateek Tripathi and according to what I understood. There are two things you need to fix in your code.

Plotting

For more information on how to 'nicely' plot check matplotlib documentation

Your implementation

Your function plotline it's acting weird and and I think it doesn't do what it should. Try with this one

def plotLine(p1, p2):
    x = (p1[0], p2[0]) # Extracting x's values of points 
    y = (p1[1], p2[1]) # Extracting y's values of points
    plt.plot(x,y, '-o',label='x,y') # Plotting points

where p1 and p2 must be tuples of the coordinates corresponding to the points of your line. The tuples can be created manually by (x1, y1) and (x2, y2); or with a function similar the next one

def coordinates2tuple(x, y):
    return (x, y)

At the end

your code could looks like

import matplotlib.pyplot as plt

def coordinates2tuple(x, y):
    return (x, y)

def plotLine(p1, p2):
    x = (p1[0], p2[0]) # Extracting x's values of points 
    y = (p1[1], p2[1]) # Extracting y's values of points
    plt.plot(x,y, '-o',label='x,y') # Plotting points
    
    
    
print('this code will plot two points in a graph and make a line')

x1 = (float(input('enter first x value: ')))
y1 = (float(input('enter first y value: ')))
x2 = (float(input('enter second x value: ')))
y2 = (float(input('enter second y value: ')))



p1 = coordinates2tuple(x1, y1)
p2 = coordinates2tuple(x2, y2)

plotLine(p1, p2)

plt.xlabel('x')
plt.ylabel('y')
plt.legend()
plt.grid()
plt.axis([-10,10,-10,10])
plt.title('two lines')
plt.show()

That with the next execution

$ python3 trs.py 
this code will plot two points in a graph and make a line
enter first x value: 0
enter first y value: 0
enter second x value: 1
enter second y value: 1

shows

edited Oct 4, 2020 at 16:05

answered Oct 4, 2020 at 15:57

bench

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3 Comments

Vro Over a year ago

the p1 and p2 needs x1 and x2 from the input. its with user input so i input the x and y values for the coordinates of the points through the console.

Vro Over a year ago

what about the second line?

bench Over a year ago

What do you mean by second line? If you only have two points you can only define one line.

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