ncoghlan@iinet.net.au wrote:
Quoting Raymond Hettinger <python@rcn.com>:
This code-snippet is littered everwhere in my applications:
string.join([str(x) for x in iterable])
Its tedious and makes code hard to read. Do we need a PEP to fix
this?
A PEP would be overkill.
Still, it would be helpful to do PEP-like things such as reference implementation, soliticing comments, keep an issue list, etc.
A minor issue is that the implementation automatically shifts to Unicode upon encountering a Unicode string. So you would need to test for this before coercing to a string.
Perhaps have string join coerce to string, and Unicode join coerce to the separator's encoding. If we do that, the existing string->Unicode promotion code should handle the switch between the two join types.
The general approach is always to coerce to Unicode if strings and Unicode meet; very much like coercion to floats is done when integers and floats meet. Your suggestion would break this logic and make coercion depend on an argument.
Also, join works in multiple passes. The proposal should be specific about where stringizing occurs. IIRC, you need the object length on the first pass, but the error handling and switchover to Unicode occur on the second.
Having been digging in the guts of string join last week, I'm pretty sure the handover to the Unicode join happens on the first 'how much space do we need' pass (essentially, all of the work done so far is thrown away, and the Unicode join starts from scratch. If you know you have Unicode, you're better off using a Unicode separator to avoid this unnecessary work </tangent>).
It's just a simple length querying loop; there's no storage allocation or anything expensive happening there, so the "throw-away" operation is not expensive. Aside: ''.join() currently only works for true sequences - not iterators. OTOH, the %-format operation is which is why PyString_Format goes through some extra hoops to make sure the work already is not dropped (indeed, it may not even be possible to reevaluate the arguments; think iterators here). We could probably add similar logic to ''.join() to have it also support iterators. -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Aug 24 2004)
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