regular expression

[Jeff Epler]

These are all untested, because I don't have Mk4py or your datafile to
try it on.

I might write this:
    import re
    pattern = re.compile("^Ge")
    def func(row):
        try:
            nachname = row.Nachname
        except AttributeError:
            return 0
        return pattern.search(nachname) is not None

    vf = vw.filter(func)

If you're using a Python version with nested scopes, you could use them
in this case:
    import re
    def make_func(pattern):
        pattern = re.compile(pattern)
        def func(row):
            try:
                nachname = row.Nachname
            except AttributeError:
                return 0
            return pattern.search(nachname) is not None
        return func

    vf = vw.filter(make_func("^Ge"))

or you can make a callable filter object by using classes:
    import re
    class PatternFilter:
        def __init__(self, pattern):
            self.pattern = re.compile(pattern)

        def __call__(self, row):
            try:
                nachname = row.Nachname
            except AttributeError:
                return 0
            return self.pattern.search(Nachname) is not None
    vf = vw.filter(PatternFilter("^Ge"))

Jeff