Re: [Python-ideas] Split, slice, join and return "syntax" for str

[Steven D'Aprano]

On Sun, Mar 04, 2018 at 12:11:16PM -0800, Michel Desmoulin wrote:

> But, first, they are not common enough so that it's hard to do:
> 
> spam = docs.python.org"
> eggs = 'wiki.' + '.'.join(spams.split('.')[1:])

In a more realistic case, the delimiter is not necessarily a constant, 
nor will you always want to replace the first item.

So you would be writing:

delimiter.join(
spam.split(delimiter)[:n-1] + 
['wiki'] + spam.split(delimiter)[n+1:]
)


Suddenly it's a lot less attractive to be typing out each time.

It is a good candidate for a helper function:

def replace_field(string, delimiter, position, new, start=0, end=None):
fields = string[start:end].split(delimiter)
fields[position] = new
string = (string[:start] + delimiter.join(fields) 
  + ('' if end is None else string[end:]))
return string

That's not the most efficient implementation, and it isn't thoroughly 
tested/debugged, but it ought to be good enough for casual use.

Personally, if this were available as a string method I think I'd use 
this quite frequently, certainly more often than I use some other string 
methods like str.partition.


> It's not that long to type, and certainly is not happening in every
> single script you do.

Speak for yourself :-)

No, not literally every script. (If that were the requirement to be a 
string method, strings would have no methods.) But I think it is common 
enough that I'd be happy for it to be a string method.


-- 
Steve
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Re: [Python-ideas] Split, slice, join and return "syntax" for str

[Steven D'Aprano]

On Sun, Mar 04, 2018 at 01:44:20PM -0500, Clint Hepner wrote:

> -1. I see no compelling reason to overload __getitem__ to provide a synonym 
> for the split method. 
> 
> eggs = "wiki." + spam.split('.')[1:]

Fair point. Neither do I. But your next comment:

> Besides, you can already make such replacements more efficiently with
> 
> eggs = spam.replace('docs', 'wiki')

is not suitable, because it assumes that the substring "docs" appears 
only once in the string.

In a more realistic example, you don't know what the string contains, 
only that it is delimited by dots and that you want to replace the n-th
field (whatever it contains) with "wiki".



-- 
Steve
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Re: [Python-ideas] Split, slice, join and return "syntax" for str

[Michel Desmoulin]

Even if replace would be a better fit, I can see why doing those 3
operations in one row can be valuable.

But, first, they are not common enough so that it's hard to do:

spam = docs.python.org"
eggs = 'wiki.' + '.'.join(spams.split('.')[1:])

It's not that long to type, and certainly is not happening in every
single script you do.

But let's say for the sake of argument you do a lot of cmd parsing, with
a lot of split and join. Just make a helper:

def rearrange(string, sep=None, start=None, stop=None, step=None):
return sep.join(string.split(sep)[start:stop:step])

And then you can do:

spam = docs.python.org"
eggs = 'wiki.' + rearrange(spam, '.', 1)

Simple, easy, no need to change Python.



Le 04/03/2018 à 09:59, Andrés Delfino a écrit :
> Hi!
> 
> I was thinking: perhaps it would be nice to be able to quicky split a
> string, do some slicing, and then obtaining the joined string back.
> 
> Say we have the string: "docs.python.org ", and
> we want to change "docs" to "wiki". Of course, there are a ton of
> simpler ways to solve this particular need, but perhaps str could have
> something like this:
> 
> spam = "docs.python.org "
> eggs = "wiki." + spam['.'][1:]
> print(eggs) #wiki.python.org 
> 
> A quick implementation to get the idea and try it:
> 
> class Mystr(str):
>     def __getitem__(self, item):
>     if isinstance(item, str):
>     return Mystr_helper(self, item)
>     else:
>     return super().__getitem__(item)
> 
> class Mystr_helper:
>     def __init__(self, obj, sep):
>     self.obj = obj
>     self.sep = sep
>     def __getitem__(self, item):
>     return self.sep.join(self.obj.split(self.sep)[item])
> 
> What are your thoughts?
> 
> Greetings from Argentina.
> 
> 
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Re: [Python-ideas] Split, slice, join and return "syntax" for str

[Clint Hepner]

> On 2018 Mar 4 , at 12:59 p, Andrés Delfino  wrote:
> 
> Hi!
> 
> I was thinking: perhaps it would be nice to be able to quicky split a string, 
> do some slicing, and then obtaining the joined string back.
> 
> Say we have the string: "docs.python.org", and we want to change "docs" to 
> "wiki". Of course, there are a ton of simpler ways to solve this particular 
> need, but perhaps str could have something like this:
> 
> spam = "docs.python.org"
> eggs = "wiki." + spam['.'][1:]
> print(eggs) #wiki.python.org

-1. I see no compelling reason to overload __getitem__ to provide a synonym for 
the split method. 

eggs = "wiki." + spam.split('.')[1:]

Besides, you can already make such replacements more efficiently with

eggs = spam.replace('docs', 'wiki')

or, for more complex replacements, 

eggs = re.sub('^docs', 'wiki', spam)

--
Clint
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[Python-ideas] Split, slice, join and return "syntax" for str

[Andrés Delfino]

Hi!

I was thinking: perhaps it would be nice to be able to quicky split a
string, do some slicing, and then obtaining the joined string back.

Say we have the string: "docs.python.org", and we want to change "docs" to
"wiki". Of course, there are a ton of simpler ways to solve this particular
need, but perhaps str could have something like this:

spam = "docs.python.org"
eggs = "wiki." + spam['.'][1:]
print(eggs) #wiki.python.org

A quick implementation to get the idea and try it:

class Mystr(str):
def __getitem__(self, item):
if isinstance(item, str):
return Mystr_helper(self, item)
else:
return super().__getitem__(item)

class Mystr_helper:
def __init__(self, obj, sep):
self.obj = obj
self.sep = sep
def __getitem__(self, item):
return self.sep.join(self.obj.split(self.sep)[item])

What are your thoughts?

Greetings from Argentina.
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