How to update a graph using matplotlib

问题

I'm using Panda and matplotlib to draw graphs in Python. I would like a live updating gaph. Here is my code:

import matplotlib.pyplot as plt
import matplotlib.animation as animation
import time
import numpy as np
import MySQLdb
import pandas

def animate():

    conn = MySQLdb.connect(host="localhost", user="root", passwd="", db="sentiment_index", use_unicode=True, charset="utf8")
    c = conn.cursor()
    query = """ SELECT t_date , score FROM mytable where t_date BETWEEN Date_SUB(NOW(), Interval 2 DAY) AND NOW()"""
    c.execute(query)
    rows=c.fetchall()
    df = pandas.read_sql(query, conn, index_col=['t_date'])

    df.plot()
    plt.show()

animate()

I thought about using FuncAnimation but didn't get the right result. Any help please?

回答1:

The documentation is a bit light on explanation of how to use FuncAnimation. However, there are examples in the gallery and blog tutorials, such as Jake Vanderplas's and Sam Dolan's PDF.

This example from Jake Vanderplas's tutorial is perhaps the "Hello World" of matplotlib animation:

from __future__ import division
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation

def init():
    return [line]

def animate(i, ax, line):
    x = np.linspace(0, 2*np.pi, N) + i/(N*2)
    ax.set_xlim(x.min(), x.max())
    line.set_data(x, np.sin(x))
    return [line]

N = 100
fig, ax = plt.subplots()
line, = ax.plot([], [])
ax.set_xlim(0, 2*np.pi)
ax.set_ylim(-1, 1)

ani = animation.FuncAnimation(
    fig, animate, init_func=init, interval=0, frames=int(4*np.pi*N), 
    repeat=True, blit=True, fargs=[ax, line])
plt.show()

Change various values or lines of code and see what happens. See what happens if you change return [line] to something else. If you study and play with these examples, you can learn how the pieces fit together.

Once you understand this example, you should be able to modify it to fit your goal.

If you have trouble, post your code and describe what error message or misbehavior you see.

Some tips:

• Since animation requires calling line.set_data, I don't think you can use Pandas' df.plot(). In fact, I'm not sure if the Pandas DataFrame is useful here. You might be better off sucking the data into lists or NumPy arrays and passing those to line.set as above, without getting Pandas involved.

• Opening a connection to the database should be done once. animate gets called many times. So it is better to define conn and c and query -- anything that does not change with each call to animate -- outside of animate, and pass them back as arguments to animate via the fargs parameter.

来源：https://stackoverflow.com/questions/31587170/how-to-update-a-graph-using-matplotlib