Hello,

as I am working out some exercises, I want to keep track of the bode plots that I am creating by providing the exercise number as the argument for the "name" parameter. However, when attempting to do so, an exception is generated because apparently periods ('.') are not acceptable. Why? A bit surprising since it is a string after all. The argument is passed in as a string, like this:

sys1 = ct.TransferFunction(l3, name='Ex. 9.4')

or, if you want to enter the transfer function as the argument so that it can be part of the graph title, as in :
'1 / (1.2s + 4.6s + 4.4s + 1)'

This is the error that is generated:

    raise ValueError(f"invalid system name '{name}' ('.' not allowed)")
ValueError: invalid system name 'Exercise 9.4' ('.' not allowed)

It consistently generates an error if a period '.' is passed in as part of the string argument.

Can the library please be improved so that this is not an issue.

Thank you.