[Python-ideas] Give regex operations more sugar
steve at pearwood.info
Thu Jun 14 02:08:00 EDT 2018
On Wed, Jun 13, 2018 at 10:43:43PM +0200, Michel Desmoulin wrote:
> str.replace come to mind. It's a annoying to have to chain it 5 times
> while we could pass optionally a tuple.
Its not so simple. Multiple replacements underspecifies the behaviour.
The simplest behaviour is to have
astring.replace((spam, eggs, cheese), new)
be simply syntactic sugar for:
astring.replace(spam, new).replace(eggs, new).replace(cheese, new)
which is nice and simple to explain and nice and simple to implement
(it's just a loop calling the method for each argument in the tuple),
but its probably not the most useful solution:
# replace any of "salad", "cheese" or "ham" with "cheesecake".
s = "Lunch course are cheese & coffee, salad & cream, or ham & peas"
s.replace("salad", "cheesecake").replace("cheese", "cheesecake").replace("ham", "cheesecake")
=> 'Lunch course are cheesecake & coffee, cheesecakecake & cream, or cheesecake & peas'
which is highly unlikely to be what anyone wants. But it isn't clear
what people *will* want.
So we need to decide what replace with multiple targets actually means.
Here are some suggestions:
- the order of targets ought to be irrelevant: replace((a, b) ...)
and replace((b, a) ...) ought to mean the same thing;
- should targets match longest first or shortest first? or a flag
to choose which you want?
- what if you have multiple targets and you need to give some longer
ones priority, and some shorter ones?
- there ought to be a single pass through the string, not multiple
passes -- this is not just syntactic sugar for calling replace in
- the replacement string should be skipped and not scanned.
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