使用plt.title()报错'str' object is not callable，赋值后标题不显示

原代码 #

#import the necessary modules
import math
import matplotlib.pyplot as plt

#initialize the two empty lists and set it as y and y2
y = []
y2 = []

#iterate through 1-10 for the value of x
for x in range(1, 11):
        #store the equation into two lists
        y += [x ** 2 + 3 - math.log(x)]
        y2 += [x ** 2 + 3 + math.log(x)]

#plot y and add the lable
plt.plot(range(1, 11), y, label = 'subtracting log(x)')

#plot y2 and add the lable, also, turn the color into red
plt.plot(range(1, 11), y2 ,color = 'red', label = 'adding log(x)')

#set the lable of x and y axis
plt.xlabel = 'x-axis'
plt.ylabel = 'y-axis'

plt.title("Plot of y = x^2 + 3 - log(x) and y = x^2 + 3 + log(x)")
plt.legend()
plt.show()

报错信息 #

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
/var/folders/8q/q_5rzwtd5qx5mpvf4r9v10_40000gn/T/ipykernel_59793/986723238.py in <module>
     23 plt.ylabel = 'y-axis'
     24 
---> 25 plt.title("Plot of y = x^2 + 3 - log(x) and y = x^2 + 3 + log(x)")
     26 plt.legend()
     27 plt.show()

TypeError: 'str' object is not callable

将plt.title("...")改为plt.title = "..."后，代码可运行但图表标题不显示，且反复触发上述报错。

错误原因 #

你把Matplotlib中设置标签、标题的函数当成普通变量赋值了：

• plt.xlabel、plt.ylabel、plt.title都是Matplotlib提供的函数，必须通过函数名(参数)的方式调用，不能直接赋值字符串。
• 执行plt.xlabel = 'x-axis'时，已经把原本的plt.xlabel函数覆盖成了字符串对象，污染了当前运行环境中的Matplotlib对象，导致后续调用plt.title时触发错误。

修正后的代码 #

把错误的赋值语句改成函数调用即可：

#import the necessary modules
import math
import matplotlib.pyplot as plt

#initialize the two empty lists and set it as y and y2
y = []
y2 = []

#iterate through 1-10 for the value of x
for x in range(1, 11):
        #store the equation into two lists
        y += [x ** 2 + 3 - math.log(x)]
        y2 += [x ** 2 + 3 + math.log(x)]

#plot y and add the lable
plt.plot(range(1, 11), y, label = 'subtracting log(x)')

#plot y2 and add the lable, also, turn the color into red
plt.plot(range(1, 11), y2 ,color = 'red', label = 'adding log(x)')

#set the lable of x and y axis - 改为函数调用
plt.xlabel('x-axis')
plt.ylabel('y-axis')

#标题用函数调用
plt.title("Plot of y = x^2 + 3 - log(x) and y = x^2 + 3 + log(x)")
plt.legend()
plt.show()

额外提示 #

如果修改后仍报错，建议重启Python内核/运行环境——之前的错误赋值已经修改了环境中的Matplotlib对象，重启后可恢复默认状态。

内容的提问来源于stack exchange，提问作者Nixon Ng