Bokeh plot title 'str' object is not callable - python-3.x

Question

In Jupyter Notebooks I read in a dataframe and create several plots with Pandas / Bokeh.
While creating one of the latter I get an error.
Search for similar problems said, that there might be somewhere above in the script something like
plt.title = "Title"
which overwrites the method. But this is not the case for me. I have nothing similar in the code above -exept in the figure parameters. Here the Bokeh documentation describes to set a figure title like I used it.
Using the part of the code that leads the the error in the complete notebook in a stand-alone script only does NOT lead to the error. So, also in my case the problem might have something to do with my code above. But maybe some of you has an idea when seeing this..(?)
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
from bokeh.plotting import figure, show, output_notebook, ColumnDataSource
from bokeh.io import output_notebook
from bokeh.layouts import column, gridplot
from bokeh.models import Label, Title
from bokeh.models import Div
data = df
output_notebook()
# Title of the overall plot
abovetitle = ("This should be the overall title of all graphs")
# GRAPH 1
s1 = figure(width = 250, plot_height = 250, title="Graph 1", x_axis_label = "axis title 1", y_axis_label = 'µs')
s1.line(x, y, width=1, color="black", alpha=1, source = data)
# s1.title.text = "Title With Options" # this is a instead-off 'title=' test, but does not solve the problem
# GRAPH 2
s2 = figure(width = 250, plot_height = 250, title="Graph 2", x_axis_label = "axis title 2, y_axis_label = 'µs')
s2.line(x, y, width=1, color="blue", alpha=1, source = data)
#s2.title.text = "Title With Options" # this is a instead-off 'title=' test, but does not solve the problem
# plot graphs:
p = gridplot([[s1, s2]])
show(column(Div(text=abovetitle), p))
leads to the type error
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-24-33e4828b986d> in <module>
31 # plot graphs:
32 p = gridplot([[s1, s2]])
---> 33 show(column(Div(text=title), p))
TypeError: 'str' object is not callable
Recalling
import matplotlib.pyplot as plt
does not solve the problem. Hence, recalling
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
from bokeh.plotting import figure, show, output_notebook, ColumnDataSource
from bokeh.io import output_notebook
from bokeh.layouts import column, gridplot
from bokeh.models import Label, Title
from bokeh.models import Div
solves the problem. Any further idea what might cause this error?
In the mean time I got a very useful hint: In one of the prior cells I accidentially used a Bokeh API function name as variable name and overwrote the function. If someone faces a comparable problem have a look at your variable naming. Maybe there happend the same accident... ;-)
#############################
# Define column names of XData binary part
header = ["Col1","Col2","Col3"]
# Split XData in single, space separated columns
x_df = selected_df.XData.str.split(' ', expand=True)
x_df.drop(0, inplace=True, axis=1)
x_df.columns = header
#print(x_df)
# Binary XData to integer
for column in x_df: # DONT DO THAT!!!!! THIS OVERWRITES BOKEH API FUNCTION. EG. USE `col` INSTEAD OF `column`
x_df[column] = x_df[column].apply(int, base=16) # DONT DO THAT!!!!! THIS OVERWRITES BOKEH API FUNCTION. EG. USE `col` INSTEAD OF `column`