Re: How to join elements at the beginning and end of the list
On Wed, 1 Nov 2017 02:29 am, Neil Cerutti wrote:
> You can use the % operator instead of +, and a generator
> expression instead of map. It's a pretty small improvement,
> though.
>
> values = '||%s||' % ('||'.join(str(s) for s in value_list))
>
> At least... I THINK you can use that generator expression in 2.7.
Generator expressions are slightly slower when you call join. If join knows
how many items there are, it can allocate space more efficiently, which is
faster.
So even though it takes a bit of time to build, and throw away, a temporary
list, its actually faster to join a list comp than a generator expression.
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Steve
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enough, things got worse.
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Re: How to join elements at the beginning and end of the list
On 10/31/17 12:29 PM, Stefan Ram wrote: Ned Batchelder writes: However you solve it, do yourself a favor and write a function to encapsulate it: It is always a good solution to encapsulate a pattern into a function. So I agree that this is a good suggestion. But just for the sole sake of information, I'd like to add that this is also the slowest solution so far (about 10.76 usec). This might be a case where macros would be fine. As readable as a function call, but no runtime-overhead. One can write value_list = [1, 2, 3, 4, 56, 's'] #define JOIN_WRAPPED(list,string) \ string + string.join(map(str,list)) + string values = JOIN_WRAPPED(value_list,'||') print( values ) and save it as »source.c« and execute it using gcc -E source.c -o source.py python source.py . This is also not intended to be a recommendation. I try to avoid micro-optimization. My guess is that right after calling wrapped_join(), the result will be written to an I/O device of some kind. If that is so, the time spent in wrapped_join will be irrelevant. --Ned. -- https://mail.python.org/mailman/listinfo/python-list
Re: How to join elements at the beginning and end of the list
On 2017-10-31, Stefan Ram wrote:
> Neil Cerutti writes:
>>You can use the % operator instead of +, and a generator
>>expression instead of map. It's a pretty small improvement,
>>though.
>
> "Improvement" in what sense?
>
> C:\>python -m timeit -s "value_list = [1, 2, 3, 4, 56, 's']" "values = '||'
> + '||'.join(map(str, value_list)) + '||'"
> 10 loops, best of 3: 4.86 usec per loop
>
> C:\>python -m timeit -s "value_list = [1, 2, 3, 4, 56, 's']" "values =
> '||%s||' % ('||'.join(str(s) for s in value_list))"
> 10 loops, best of 3: 7.46 usec per loop
Hmmm minty freshness?
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Neil Cerutti
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Re: How to join elements at the beginning and end of the list
On 10/31/17 11:29 AM, Neil Cerutti wrote:
On 2017-10-31, Ganesh Pal wrote:
Here is my solution
values = '||' + '||'.join(map(str, value_list)) + '||'
values
'||1||2||3||4||56||s||'
I am joining the elements at the beginning and end of the list
using '+' operator any other solution, this is not looking
neater
I am a Linux user using python 2.7
You can use the % operator instead of +, and a generator
expression instead of map. It's a pretty small improvement,
though.
values = '||%s||' % ('||'.join(str(s) for s in value_list))
At least... I THINK you can use that generator expression in 2.7.
However you solve it, do yourself a favor and write a function to
encapsulate it:
def wrapped_join(values, sep):
"""Join values with sep, and also include sep at the ends."""
return "{sep}{vals}{sep}".format(sep=sep, vals=sep.join(str(v)
for v in values))
--Ned.
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Re: How to join elements at the beginning and end of the list
On 2017-10-31, Ganesh Pal wrote:
> Here is my solution
>
values = '||' + '||'.join(map(str, value_list)) + '||'
values
>
> '||1||2||3||4||56||s||'
>
> I am joining the elements at the beginning and end of the list
> using '+' operator any other solution, this is not looking
> neater
>
> I am a Linux user using python 2.7
You can use the % operator instead of +, and a generator
expression instead of map. It's a pretty small improvement,
though.
values = '||%s||' % ('||'.join(str(s) for s in value_list))
At least... I THINK you can use that generator expression in 2.7.
--
Neil Cerutti
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