[Python-ideas] string.replace should accept a list as a first argument

[Ryan Gonzalez]

Would you happen to have anything to do with the creation of the regex module?

Just curious. ;)

On October 6, 2015 9:24:40 PM CDT, MRAB <python at mrabarnett.plus.com> wrote:
>On 2015-10-07 02:30, Steven D'Aprano wrote:
>> On Tue, Oct 06, 2015 at 06:34:16PM +0200, M.-A. Lemburg wrote:
>>> On 06.10.2015 21:25, Emil Rosendahl Petersen wrote:
>>> > I think string.replace should be changed accept a list as a first
>>> > argument.
>>> >
>>> > That way, if I had this string:
>>> >
>>> > "There are a lot of undesirable people in this filthy world"
>>> >
>>> > Then I could do this, replace(['undesirable', 'filthy'], ''), in
>case
>>> > that's what I wanted to do.
>>> >
>>> > Now, string.replace doesn't accept a list as its first argument,
>and
>>> > complains about implicit conversion.
>>
>> [Emil]
>>> > Is there any great obstacle to just having the function loop over
>that
>>> > list, calling itself in case we get a list argument instead of a
>str?
>>
>> Looping over each replacement item is the wrong solution. Think of
>> the result when one of the search strings is a substring of the
>> replacement:
>>
>> py> source = "I ate a chicken salad, and she had a ham sandwich."
>> py> for term in ["ham", "turkey", "chicken", "spam"]:
>> ...     source = source.replace(term, "spam and cheese")
>> ...
>> py> print(source)
>> I ate a spam and cheese and cheese salad, and she had a spam and
>cheese
>> and cheese sandwich.
>>
>>
>> You need to be a bit more careful about how to do the replacements.
>>
>>
>>> > Doesn't that seem like the more obvious behaviour? To me the
>results of
>>> > running the above code should be unsurprising, if this change was
>>> > implemented: "there are a lot of people in this world".
>>
>> [MAL]
>>> I think the "one obvious way" of doing a multi-replace is to
>>> use the re module, since implementing this efficiently is
>>> non-trivial.
>>>
>>> String methods are meant to be basic (high performance)
>>> operations.
>>
>> A similar issue was discussed last month, in the context of str.split
>> rather than replace, and I talked about the pitfalls of using the re
>> module:
>>
>>
>https://mail.python.org/pipermail/python-ideas/2015-September/036586.html
>>
>>
>> The implementation isn't hard, but it's just tricky enough that some
>> people will get it wrong, and just useful enough that a helper
>function
>> will be a good idea. The question is, should that helper function be
>a
>> string method, in the standard library, or merely something that you
>add
>> to your own projects?
>>
>> def replace_all(source, old, new, count=None):
>>      if isinstance(old, str):
>>          return source.replace(old, new, count)
>>      elif isinstance(old, tuple)
>>          regex = '|'.join(re.escape(s) for s in old)
>>          return new.join(re.split(regex, source, count))
>>
>>
>Again, using the regex module, you can split on a named list, without
>having to worry about sorting or escaping the items. :-)
>
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