It looks as if len returns the lenght of an UTF8 string
even if the string
only contains ascii characters and default encoding is
ascii. This
means that if you insert f. ex. one danish ø in a
string. len will return a
value of 2. i.e.

a='ø'
print len(a)

gives:
2

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How are you getting your danish character into the string?  If it's by typing 
it into a console, is your console in utf-8 mode?

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Actually the problem persists whether i am reading from a
file or inputting from a keyboard. I am using python from the
command line in linux shell. I dont know what console that is.
But it is able to show the danish characters on the screen as 
well as reading them from the keyboard.

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Well, what encoding is the file in?

I suspect that it's in utf-8, so when you open the file and
call read() you get utf-8 data and thus your danish
character is represented as two bytes.

You might want to do 

import codecs
fileobj = codecs.open('filename.txt', encoding='utf-8')

and then fileobj.read() will return a unicode string of the
length you're expecting.

At any rate, I see no evidence of a Python bug here, so closing.

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Yes, you are right, the problem is that the console-thingy 
converts my iso8859 characters to utf-8. Thanks for the
explanation.