## The Question :

*308 people think this question is useful*

**TL;DR ->** How can one create a legend for a line graph in `Matplotlib`

‘s `PyPlot`

without creating any extra variables?

Please consider the graphing script below:

if __name__ == '__main__':
PyPlot.plot(total_lengths, sort_times_bubble, 'b-',
total_lengths, sort_times_ins, 'r-',
total_lengths, sort_times_merge_r, 'g+',
total_lengths, sort_times_merge_i, 'p-', )
PyPlot.title("Combined Statistics")
PyPlot.xlabel("Length of list (number)")
PyPlot.ylabel("Time taken (seconds)")
PyPlot.show()

As you can see, this is a very basic use of `matplotlib`

‘s `PyPlot`

. This ideally generates a graph like the one below:

Nothing special, I know. However, it is unclear what data is being plotted where (I’m trying to plot the data of some sorting algorithms, length against time taken, and I’d like to make sure people know which line is which). Thus, I need a legend, however, taking a look at the following example below(from the official site):

ax = subplot(1,1,1)
p1, = ax.plot([1,2,3], label="line 1")
p2, = ax.plot([3,2,1], label="line 2")
p3, = ax.plot([2,3,1], label="line 3")
handles, labels = ax.get_legend_handles_labels()
# reverse the order
ax.legend(handles[::-1], labels[::-1])
# or sort them by labels
import operator
hl = sorted(zip(handles, labels),
key=operator.itemgetter(1))
handles2, labels2 = zip(*hl)
ax.legend(handles2, labels2)

You will see that I need to create an extra variable `ax`

. How can I add a legend to my graph *without* having to create this extra variable and retaining the simplicity of my current script?

*The Question Comments :*

## The Answer 1

*520 people think this answer is useful*

Add a `label=`

to each of your `plot()`

calls, and then call `legend(loc='upper left')`

.

Consider this sample (tested with Python 3.8.0):

import numpy as np
import matplotlib.pyplot as plt
x = np.linspace(0, 20, 1000)
y1 = np.sin(x)
y2 = np.cos(x)
plt.plot(x, y1, "-b", label="sine")
plt.plot(x, y2, "-r", label="cosine")
plt.legend(loc="upper left")
plt.ylim(-1.5, 2.0)
plt.show()

Slightly modified from this tutorial: http://jakevdp.github.io/mpl_tutorial/tutorial_pages/tut1.html

## The Answer 2

*39 people think this answer is useful*

You can access the Axes instance (`ax`

) with `plt.gca()`

. In this case, you can use

plt.gca().legend()

You can do this either by using the `label=`

keyword in each of your `plt.plot()`

calls or by assigning your labels as a tuple or list within `legend`

, as in this working example:

import numpy as np
import matplotlib.pyplot as plt
x = np.linspace(-0.75,1,100)
y0 = np.exp(2 + 3*x - 7*x**3)
y1 = 7-4*np.sin(4*x)
plt.plot(x,y0,x,y1)
plt.gca().legend(('y0','y1'))
plt.show()

However, if you need to access the Axes instance more that once, I do recommend saving it to the variable `ax`

with

ax = plt.gca()

and then calling `ax`

instead of `plt.gca()`

.

## The Answer 3

*14 people think this answer is useful*

Here’s an example to help you out …

fig = plt.figure(figsize=(10,5))
ax = fig.add_subplot(111)
ax.set_title('ADR vs Rating (CS:GO)')
ax.scatter(x=data[:,0],y=data[:,1],label='Data')
plt.plot(data[:,0], m*data[:,0] + b,color='red',label='Our Fitting
Line')
ax.set_xlabel('ADR')
ax.set_ylabel('Rating')
ax.legend(loc='best')
plt.show()

## The Answer 4

*13 people think this answer is useful*

A simple plot for sine and cosine curves with a legend.

Used `matplotlib.pyplot`

import math
import matplotlib.pyplot as plt
x=[]
for i in range(-314,314):
x.append(i/100)
ysin=[math.sin(i) for i in x]
ycos=[math.cos(i) for i in x]
plt.plot(x,ysin,label='sin(x)') #specify label for the corresponding curve
plt.plot(x,ycos,label='cos(x)')
plt.xticks([-3.14,-1.57,0,1.57,3.14],['-$\pi$','-$\pi$/2',0,'$\pi$/2','$\pi$'])
plt.legend()
plt.show()

## The Answer 5

*7 people think this answer is useful*

Add labels to each argument in your plot call corresponding to the series it is graphing, i.e. `label = "series 1"`

Then simply add `Pyplot.legend()`

to the bottom of your script and the legend will display these labels.

## The Answer 6

*5 people think this answer is useful*

You can add a custom legend documentation

first = [1, 2, 4, 5, 4]
second = [3, 4, 2, 2, 3]
plt.plot(first, 'g--', second, 'r--')
plt.legend(['First List', 'Second List'], loc='upper left')
plt.show()

## The Answer 7

*0 people think this answer is useful*

# Dependencies
import numpy as np
import matplotlib.pyplot as plt
#Set Axes
# Set x axis to numerical value for month
x_axis_data = np.arange(1,13,1)
x_axis_data
# Average weather temp
points = [39, 42, 51, 62, 72, 82, 86, 84, 77, 65, 55, 44]
# Plot the line
plt.plot(x_axis_data, points)
plt.show()
# Convert to Celsius C = (F-32) * 0.56
points_C = [round((x-32) * 0.56,2) for x in points]
points_C
# Plot using Celsius
plt.plot(x_axis_data, points_C)
plt.show()
# Plot both on the same chart
plt.plot(x_axis_data, points)
plt.plot(x_axis_data, points_C)
#Line colors
plt.plot(x_axis_data, points, "-b", label="F")
plt.plot(x_axis_data, points_C, "-r", label="C")
#locate legend
plt.legend(loc="upper left")
plt.show()