Strange error with matplotlib axes labels

Question

I'm very new to Python and programming in general, so apologies in advance if I'm missing something obvious. I'm trying to plot a graph and label the axes, but every time I try to label the y axis an exception is raised. I wrote the code below in a new script to make sure the problem wasn't coming from somewhere else in the module. I'm using Python 3.4.

from numpy import * from matplotlib import *  a = [1, 2, 3, 4, 5] b = [2, 3, 2, 3, 2] pyplot.plot(a, b) pylab.xlabel("Time") pylab.ylabel("Speed") 

Every time, I get the error 'TypeError: 'str' object is not callable' for the final line. If I change the y to an x, everything is fine. If I change the x to a y, I get the same error. However, ylabel comes up on the drop down list for ylabel so the function does exist and the documentation says a string is the only necessary argument, exactly as for xlabel (matplotlib.pyplot.ylabel(s, *args, **kwargs) and matplotlib.pyplot.xlabel(s, *args, **kwargs)). What on earth could be going on here?

Answer 1

I had this same issue when working in iPython notebook.

I think it can be re-created as follows:

import matplotlib.pyplot as plt plt.ylabel = 'somestring' # oh wait this isn't the right syntax. ...  plt.ylabel('somestring') # now this breaks because the function has been turned into a string 

Re-starting the kernel or re-importing the libraries restores plt.ylabel to a function.