Formatting matplotlib x limits

Question

x = np.linspace(2000.0, 2018.0, num = 18)

for i in range(len(x)):
    x[i]=int(x[i])


for i in range(2000, 2018):
    y.append(dic[str(i)])


fig, ax = plt.subplots()

ax.plot(x, y, marker='o', color='r')

# set title

# set label for x

# set label for y

print(ax.get_xlim())

return ax

I am trying to plot a 18 points where x limit should be from (2000.0) to (2018.0). Some codes are hidden, but I just posted the critical parts. When I print the result out, the xlimit is

(1999.0999999999999, 2018.9000000000001)

not

(2000.0, 2018.0)

Please tell me what I am doing wrong.

Answer 1

You'll need to set the xlim yourself. matplotlib automatically select the limits and ticks.

so you need to use

ax.set_xlim([x[0],x[-1]])

For the xlim to be exactly what you want.

see plot below

Answer 2

You are not doing anything wrong; but you may have the wrong expectation concerning the limits of the plot.

By default, matplotlib leaves 5% margin on each side of the plot. Hence, if your data is in the range [x.min(), x.max()] == [2000.0, 2018.0] your limits will be

[x.min()-0.05*(x.max()-x.min()), x.max()+0.05*(x.max()-x.min())] == [1999.1, 2018.9]

If you don't want to have any padding around your data, use ax.margins(x=0) . In that case print(ax.get_xlim()) will print (2000.0, 2018.0)

Complete example:

import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(2000.0, 2018.0, num = 19)
y = np.cumsum(np.random.rand(len(x)))

x = x.astype(int)

fig, ax = plt.subplots()

ax.plot(x, y, marker='o', color='r')
ax.margins(x=0)

print(ax.get_xlim())