How to show source code of a package function in IPython notebook

For teaching purposes I want an IPython notebook that displays (as output from a cell) the function source code, but I want to be able to reference this in multiple notebooks. Hence I would like to display the function code, in a similar way to using the %psource magic, but appropriately syntax highlighted.

This is a similar question to this question, but I want to be able to apply it to a single function within a file, rather than to the complete file at once.

Using the suggestion from the previous question I hacked a short code that works in simple cases:

def print_source(module, function):
    """For use inside an IPython notebook: given a module and a function, print the source code."""
    from inspect import getmembers, isfunction, getsource
    from pygments import highlight
    from pygments.lexers import PythonLexer
    from pygments.formatters import HtmlFormatter
    from IPython.core.display import HTML

    internal_module = __import__(module)

    internal_functions = dict(getmembers(internal_module, isfunction))

    return HTML(highlight(getsource(internal_functions[function]), PythonLexer(), HtmlFormatter(full=True)))

Two questions:

1. This gist suggests that showing the whole function could be done by defining appropriate cell magic. Is it possible to define an appropriate cell magic to just show a single function, as above?
2. Is there a way of doing this without importing the entire module, or a more robust way of doing this?