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Script Tool Fails when Adding a Legend

Question asked by pamccord on Jun 13, 2018
Latest reply on Jun 13, 2018 by Dan_Patterson

I have a Python script that I'm using in a script tool in ArcToolbox. This script reads FAO food security indicator data and then plots the data for a country that the user chooses. When I run the script outside of ArcGIS, it plots the data with no issues.

However, when the script tool is run within ArcGIS, I receive an error the second time it is run. The error is:


"An error occurred: expected string or buffer"


The first time the script tool runs, everything works fine: it outputs a figure with food security information. It's the second time I run the tool that it fails and returns the above error.

A similar question was asked here: Arc Toolbox Python script tool plot legend error  

And ultimately the solution that was arrived at was to restart ArcGIS. When I restart ArcGIS, I am able to successfully run the tool again, but, as expected, it fails on the subsequent run. This will be inconvenient for the users of this tool since I don't want them to have to restart ArcGIS every time they run the tool for a different country or different food security indicator.

I've identified in the script where the issue occurs. I've imported matplotlib.pyplot as plt, and when my script includes 'plt.legend' in order to add a legend to the figure, this is what causes the script to fail on the second run. If I remove plt.legend from the script, I can run the tool as many times in succession as I want without an error (unfortunately, the plots that are created no longer have a legend).

Has anyone encountered this issue in the past? If so, have you found a way to overcome this without restarting ArcGIS every time?  


Here's my code where I add the legend:


plt.figure(figsize = (12, 9))

ax = plt.subplot(111)



ax.tick_params(axis = "both", labelsize = 10)

lineDrawType = [(5, 2, 20, 2), (2, 5), (4, 4, 2, 2), (4, 10), (5, 2)]

obsList = [iso_code, "lowestIncome", "midLowerIncome", "midUpperIncome", "uppermostIncome"]

labelObsNames = [countryName, "Low-Income", "Lower-Middle-Income", "Upper-Middle-Income", "High-Income"]

for rank, locationName in enumerate(obsList):

            df_plot = df_selected[df_selected["ISO_code"] == locationName]                                 

            plt.plot(df_plot["YearEnd"], df_plot["Value"], lw = 3., color = tableau[rank], ls = "--", dashes = lineDrawType[rank],             label = labelObsNames[rank])

artList = []

lgdPlotter = plt.legend(loc = "upper center", bbox_to_anchor = (0.5, -0.1), ncol=3)


plt.savefig(os.path.join(outputLocation, "test2.png"), additional_artists = artList, bbox_inches = "tight")