This is straight from the library (xml.sax.saxutils)
[chosen more because so at least it's real code than because nobody can argue
that it is irrelevant. I find fascinating how much powerful is the argument
"nobody does that often" in discussions about language design]
def prepare_input_source(source, base = ""):
"""This function takes an InputSource and an optional base URL and
returns a fully resolved InputSource object ready for reading."""
if type(source) in _StringTypes:
source = xmlreader.InputSource(source)
elif hasattr(source, "read"):
f = source
source = xmlreader.InputSource()
source.setByteStream(f)
if hasattr(f, "name"):
source.setSystemId(f.name)
...
the first problem is the "ontology" problem and how much we want to support
someone who want to strictly check
(a) "source has intentionally a file-like read" vs. just
(b) "source has some read method"...
This is indipendent of whether we have adapt or declarative interfaces or both.
The above could be written as:
source = adapt(source,xmlreader.InputSource)
moving the code inside xmlreader.InputSource.__adapt__ .
But does this address (a)?
I would say no.
Then one could simply not implement __adapt__ but leave the burden to the users
to define my-type-with-a-good-read
to xmlreader.InputSource adaptations. Or put code the code inside
xmlreader.InputSource.__adapt__
and susbitute
elif hasattr(source, "read"):
with
f = adapt(source,???)
so the "ontology" problem is back.
My point is not against adaptation, but that adaptation does not automagically
solve all our problems without further thinking.
I repeat, with both adaptation and interfaces, if one cares about contracts vs.
just signatures, the ontology problem is with us.
Adaptation is probably expressive enough. But the choice between
(I)
- mechanisms to ask and declare whether object implements protocol
- mechanisms to register adapter factories between protocol A and B
[I think this is Zope3 model]
or
(II)
- just adaptation
should be a choice also about convenience, readability, ...
both ways the ontology problem is there.
regards.
RetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4