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Given the following text description, write Python code to implement the functionality described below step by step
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Description:
 Plot Type Selector
Example showing how to construct a dropdown widget that can be used to select a plot type.  Here a dictionary must be used for the plot type options.
Step1:  Load cube.
Step2:  Compose and sort a dictionary of plot-types and then construct widget to present them, along with a default option. Display the widget using the IPython display call.
Step3:  Print selected widget value for clarity.
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Python Code:
import ipywidgets
import IPython.display
import iris
import numpy as np
import iris.quickplot as iplt
import matplotlib.pyplot as plt
Explanation: Plot Type Selector
Example showing how to construct a dropdown widget that can be used to select a plot type.  Here a dictionary must be used for the plot type options.
End of explanation
cube = iris.load_cube(iris.sample_data_path('A1B.2098.pp'))
print cube
Explanation: Load cube.
End of explanation
plot_type_dict = {'contour': iplt.contour, 'contourf': iplt.contourf, 'pcolor': iplt.pcolor, 'outline': iplt.outline,
                  'pcolormesh': iplt.pcolormesh, 'plot': iplt.plot, 'points': iplt.points}
plot_types = plot_type_dict.keys()
sorted(plot_types)
im = ipywidgets.Dropdown(
    description='Plot-type:',
    options=plot_types,
    value='contour')
IPython.display.display(im)
Explanation: Compose and sort a dictionary of plot-types and then construct widget to present them, along with a default option. Display the widget using the IPython display call.
End of explanation
print im.value
Explanation: Print selected widget value for clarity.
End of explanation
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