does lack of type declarations make Python unsafe?

Bengt Richter bokr at
Wed Jun 18 18:35:16 CEST 2003

On Wed, 18 Jun 2003 10:25:54 -0400, David Abrahams <dave at> wrote:

>Alex Martelli <aleax at> writes:
>> But this has little to do with the need of 'type declarations'.  I
>> suspect that a statically typed language would also be better off
>> without them, relying on type inferencing instead, a la Haskell (and
>> Haskell's typeclasses to keep the inferencing as wide as feasible),
>> for example.  But I have no research to back this up;-).
>I don't have any first-hand experience, but the experience of friends
>of mine who have used Haskell is that it can be exceedingly difficult
>to locate the source of a type error when it does occur, since the
>inference engine may propagate the "wrong" type back much further than
>the source of the error.
>Furthermore, if you do everything by inference you lose the
>explanatory power of type declarations.
But what does "type" really mean? ISTM that in the static typing world
"type" mostly identifies a type of *representation* -- i.e., things that
have compatible memory layouts. Of course any Python implementation will
have underlying *representations* of its entities, but those are not a
central concern of Python or Python programmers. In fact, UIAM it is a
goal of Python design to enable programmers to forget about concrete
representations as much as possible, except for "foreign" interfacing.

I.e., the "types" of Python are more abstract, and are more about
abstract structure and functional compatibility than underlying
representation. ISTM "static" typing in this world can't be a direct
translation of the old concept, unless you are talking about an interface
to an old-style "statically typed" world, or want to incorporate
an encapsulated chunk of that into python.

Bengt Richter

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