what is the role of bins to plot an histogram? : I want to an histogram. When I plot it with `bins=80` or `auto`. My code works correctly. But when I try to plot it with `bins=100`. It does not work with giving me this error:

        "{!r} is not a valid estimator for `bins`".format(bin_name))
    ValueError: '100' is not a valid estimator for `bins`


This is my code: 

    import matplotlib.pyplot as plt
    x= [81.70900202536467, 81.69066539803865, 81.9634647036723, 81.6886583191991, 81.70063595809025, 81.71279936786232, 81.6846428541525]
    plt.hist(x,bins='100')
    plt.hist(x)
    plt.show()

What is the role of bins with histogram?  how to choose the suitable bins value for my data? 