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Adding static typing to Python

Laura Creighton lac at strakt.com
Thu Feb 21 02:50:03 EST 2002 
> Alexander Jerusalem:
> The proposals of the types-SIG say that static typing is used on a per
> module basis. That means that weather there is or is not a performance
> improvement it's only going to affect you if you choose to use the
> static types.
> 
> Alexander

The problem is that static typing effects everybody in terms of code
reusability.  Let us say you make a terrific function which works on 
a string.  And in some way you specify that, yes, the first and only
argument to this function is a string.  

Now, let us assume I love your function and want to use it a lot.
But I want to use it on my own objects which are in some way 'string
like'.  Right now I have to read your code, and determine what
were the properties of a string you used, to determine whether my
stringlike object can already be used with your function.  I would
like to automate this, and be able to interrogate both your function
and my object and get a result  'will work' or 'won't work: reason
object does not have an islower method which function requires' and 
the like.

What I don't want to have to do is rewrite the code, because
Alexander Jerusalem was only thinking about strings when he wrote it.
Static type checking makes you think that 'strings' and 'ints' and the
like a real meaningful things rather than a convenient shorthand for
'is a sequence and has the following methods':

['capitalize', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find',
 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle',
 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'replace', 'rfind', 'rindex',
 'rjust', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase',
 'title', 'translate', 'upper']

See 'PEP 246: Object Adaptation - (Clark C. Evans)'
http://python.sourceforge.net/peps/pep-0246.html  for one attempt to
get the safety you want without the restriction I don't.

Laura Creighton
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