Re: The inverse of .join
On 2010-06-18, Jon Clements wrote:
>> I just wondered if something smoother was available.
>
> In terms of behaviour and 'safety', I'd go for:
>
rec = { 'code1': '1,2,3', 'code2': '' }
next(csv.reader([rec['code1']]))
> ['1', '2', '3']
next(csv.reader([rec['code2']]))
> []
Slick!
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Neil Cerutti
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Re: The inverse of .join
On 17 June, 21:03, Neil Cerutti wrote:
> On 2010-06-17, Robert Kern wrote:
>
> > On 6/17/10 2:08 PM, Neil Cerutti wrote:
> >> On 2010-06-17, Ian Kelly wrote:
> >>> On Thu, Jun 17, 2010 at 11:45 AM, Neil Cerutti
> >>> wrote:
> What's the best way to do the inverse operation of the .join
> function?
>
> >>> Use the str.split method?
>
> >> split is perfect except for what happens with an empty string.
>
> > Why don't you try it and find out?
>
> I'm currently using the following without problems, while reading
> a data file. One of the fields is a comma separated list, and may
> be empty.
>
> f = rec['codes']
> if f == "":
> f = []
> else:
> f = f.split(",")
>
> I just wondered if something smoother was available.
>
> --
> Neil Cerutti
In terms of behaviour and 'safety', I'd go for:
>>> rec = { 'code1': '1,2,3', 'code2': '' }
>>> next(csv.reader([rec['code1']]))
['1', '2', '3']
>>> next(csv.reader([rec['code2']]))
[]
hth
Jon.
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Re: The inverse of .join
On 2010-06-18, Steven D'Aprano wrote:
> On Thu, 17 Jun 2010 20:03:42 +, Neil Cerutti wrote:
>> I'm currently using the following without problems, while
>> reading a data file. One of the fields is a comma separated
>> list, and may be empty.
>>
>> f = rec['codes']
>> if f == "":
>> f = []
>> else:
>> f = f.split(",")
>>
>> I just wondered if something smoother was available.
>
> Seems pretty smooth to me. What's wrong with it? I assume
> you've put it into a function for ease of use and reduction of
> code duplication.
The part that's wrong with it, and it's probably my fault, is
that I can never think of it. I had to go dig it out of my code
to remember what the special case was.
> You could also use the ternary operator, in which case it's a
> mere two- liner and short enough to inline wherever you need
> it:
>
> f = rec['codes']
> f = f.split(",") if f else []
That's pretty cool.
Thanks to everybody for their thoughts.
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Re: The inverse of .join
On Thu, 17 Jun 2010 20:03:42 +, Neil Cerutti wrote:
> I'm currently using the following without problems, while reading a data
> file. One of the fields is a comma separated list, and may be empty.
>
> f = rec['codes']
> if f == "":
> f = []
> else:
> f = f.split(",")
>
> I just wondered if something smoother was available.
Seems pretty smooth to me. What's wrong with it? I assume you've put it
into a function for ease of use and reduction of code duplication.
You could also use the ternary operator, in which case it's a mere two-
liner and short enough to inline wherever you need it:
f = rec['codes']
f = f.split(",") if f else []
--
Steven
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Re: The inverse of .join
On Thu, 17 Jun 2010 20:44:41 +0100, MRAB wrote: > Should .split grow an addition keyword argument to specify the desired > behaviour? Please no. > (Although it's simple enough to define your own function.) Exactly. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: The inverse of .join
On Thu, 17 Jun 2010 17:45:41 +, Neil Cerutti wrote:
> What's the best way to do the inverse operation of the .join function?
str.join is a many-to-one function, and so it doesn't have an inverse.
You can't always get the input back unchanged:
>>> L = ["a", "b", "c|d", "e"]
>>> s = '|'.join(L)
>>> s
'a|b|c|d|e'
>>> s.split('|')
['a', 'b', 'c', 'd', 'e']
There's no general way of getting around this -- if split() takes input
"a|b|c", there is no way even in principle for it to know which of these
operations it should reverse:
"|".join(["a", "b", "c"])
"|".join(["a|b", "c"])
"|".join(["a", "b|c"])
"|".join(["a|b|c"])
"b".join(["a|", "|c"])
The behaviour with the empty string is just a special case of this.
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Re: The inverse of .join
On 6/17/10 3:03 PM, Neil Cerutti wrote: On 2010-06-17, Robert Kern wrote: On 6/17/10 2:08 PM, Neil Cerutti wrote: On 2010-06-17, Ian Kelly wrote: On Thu, Jun 17, 2010 at 11:45 AM, Neil Cerutti wrote: What's the best way to do the inverse operation of the .join function? Use the str.split method? split is perfect except for what happens with an empty string. Why don't you try it and find out? I would like to apologize. I read that sentence as a question for some reason. That said, it always helps for you to show the results that you are getting (and the code that gives those results) and state what results you were expecting. -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list
Re: The inverse of .join
On 2010-06-17, Robert Kern wrote:
> On 6/17/10 2:08 PM, Neil Cerutti wrote:
>> On 2010-06-17, Ian Kelly wrote:
>>> On Thu, Jun 17, 2010 at 11:45 AM, Neil Cerutti
>>> wrote:
What's the best way to do the inverse operation of the .join
function?
>>>
>>> Use the str.split method?
>>
>> split is perfect except for what happens with an empty string.
>
> Why don't you try it and find out?
I'm currently using the following without problems, while reading
a data file. One of the fields is a comma separated list, and may
be empty.
f = rec['codes']
if f == "":
f = []
else:
f = f.split(",")
I just wondered if something smoother was available.
--
Neil Cerutti
--
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Re: The inverse of .join
On 6/17/10 12:44 PM, MRAB wrote:
> Neil Cerutti wrote:
>> On 2010-06-17, Ian Kelly wrote:
>>> On Thu, Jun 17, 2010 at 11:45 AM, Neil Cerutti
>>> wrote:
What's the best way to do the inverse operation of the .join
function?
>>> Use the str.split method?
>>
>> split is perfect except for what happens with an empty string.
>>
> I see what you mean.
>
> This is consistent:
>
','.join([''])
> ''
''.split(',')
> ['']
>
> but this isn't:
>
','.join([])
> ''
''.split(',')
> ['']
>
> An empty string could be the result of .join(['']) or .join([]).
>
> Should .split grow an addition keyword argument to specify the desired
> behaviour? (Although it's simple enough to define your own function.)
Guido finds keyword-arguments-to-change-behavior to be unPythonic, IIRC.
It generally means 'make a new API'. But, the question is-- is it worth
the mental strain of a new API?
This is such an extreme edge case, having to do:
if blah:
result = blah.split(',')
else:
result = []
Is really not asking too much, I think.
--
Stephen Hansen
... Also: Ixokai
... Mail: me+list/python (AT) ixokai (DOT) io
... Blog: http://meh.ixokai.io/
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Re: The inverse of .join
On 6/17/10 2:08 PM, Neil Cerutti wrote: On 2010-06-17, Ian Kelly wrote: On Thu, Jun 17, 2010 at 11:45 AM, Neil Cerutti wrote: What's the best way to do the inverse operation of the .join function? Use the str.split method? split is perfect except for what happens with an empty string. Why don't you try it and find out? -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list
Re: The inverse of .join
Neil Cerutti wrote:
On 2010-06-17, Ian Kelly wrote:
On Thu, Jun 17, 2010 at 11:45 AM, Neil Cerutti
wrote:
What's the best way to do the inverse operation of the .join
function?
Use the str.split method?
split is perfect except for what happens with an empty string.
I see what you mean.
This is consistent:
>>> ','.join([''])
''
>>> ''.split(',')
['']
but this isn't:
>>> ','.join([])
''
>>> ''.split(',')
['']
An empty string could be the result of .join(['']) or .join([]).
Should .split grow an addition keyword argument to specify the desired
behaviour? (Although it's simple enough to define your own function.)
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Re: The inverse of .join
On 2010-06-17, Ian Kelly wrote: > On Thu, Jun 17, 2010 at 11:45 AM, Neil Cerutti > wrote: >> What's the best way to do the inverse operation of the .join >> function? > > Use the str.split method? split is perfect except for what happens with an empty string. -- Neil Cerutti -- http://mail.python.org/mailman/listinfo/python-list
Re: The inverse of .join
On Thu, Jun 17, 2010 at 11:45 AM, Neil Cerutti wrote: > What's the best way to do the inverse operation of the .join > function? Use the str.split method? -- http://mail.python.org/mailman/listinfo/python-list
Re: The inverse of .join
Neil Cerutti wrote: What's the best way to do the inverse operation of the .join function? .split, possibly, although there will be problems if the string contains other occurrences of the separator. -- http://mail.python.org/mailman/listinfo/python-list
Re: The inverse of .join
Neil Cerutti wrote: > What's the best way to do the inverse operation of the .join > function? > > -- > Neil Cerutti split -- http://mail.python.org/mailman/listinfo/python-list
The inverse of .join
What's the best way to do the inverse operation of the .join function? -- Neil Cerutti -- http://mail.python.org/mailman/listinfo/python-list
