Static typing

Shane Hathaway shane at
Sat Jul 26 00:39:25 CEST 2003

Bjorn Pettersen wrote:
>>From: Shane Hathaway [mailto:shane at] 
>>def foo(bar, baz):
>>     assert isinstance(bar, int)
>>     assert isinstance(baz, str)
> [...]
> ...which means you can't use foo with unicode strings or UserStrings,

That's right, and that's intentional.  The function is designed to work 
only with byte arrays.  This invites someone who wants to pass a unicode 
object to first verify that the function will actually work properly 
with unicode.

> etc., etc. This is C programming in Python, ugly, inefficient,
> inflexible, and un-Pythonic.

It is highly useful documentation.  There is nothing inefficient about 
it.  It is as flexible as the programmer makes it.  It is quite 
Pythonic, although you should only declare the types of arguments when 
the type matters.

I should say that in actual practice, I haven't used isinstance() 
checks.  Instead, I've been checking against Zope interfaces.

def foo(conn):
   assert IDatabaseConnection.isImplementedBy(conn)


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