[Tutor] Pythonic way of concatenation of elements in an array

[spawgi at gmail.com]

Hello Steven,

Thanks a lot for the detailed answer. I will implement your suggestions.
Really appreciate it.

Thanks and Regards,
Sumod

On Fri, Jan 27, 2012 at 4:34 AM, Steven D'Aprano <steve at pearwood.info>wrote:

> spawgi at gmail.com wrote:
>
>> Hello,
>>
>> My code is -
>>
>> l = len(m)
>> item = str(m[1])
>> for i in range(2,l):
>>    item = item + "-" + str(m[i])
>>
>> This code is part of a bigger function. It works fine. But I am not happy
>> with the way I have written it. I think there is a better (Pythonic) way
>> to
>> rewrite it.
>> If anyone knows how to improve this snippet, I would be very thankful.
>>
>
> (1) Never use "l" as a variable name, as it looks too much like 1.
>
>
> (2) Use meaningful names. When posting snippets for help, you should show
> example data.
>
>
> (3) You almost never need to iterate over an index by hand. Instead
> iterate over the items themselves. That is, instead of this:
>
> for i in len(sequence):
>    do_something_with( sequence[i] )
>
> do this instead:
>
> for item in sequence:
>    do_something_with( item )
>
>
> and similar variations.
>
>
> (4) When you want only part of a sequence, use slicing to extract just the
> parts you care about.
>
>
> (5) When assembling strings from substrings, never use repeated
> concatenation using + as that can be EXTREMELY slow. Use str.join to build
> the string in one assignment, instead of multiple assignments.
>
> Your code shown above is *very* inefficient and will be PAINFULLY slow if
> m is very large. To understand why, you should read this article:
>
> http://www.joelonsoftware.com/**articles/fog0000000319.html<http://www.joelonsoftware.com/articles/fog0000000319.html>
>
> In this case, you can replace your snippet with this:
>
> result = '-'.join(str(item) for item in m[1:])
>
>
>
> For example:
>
> py> m = [1, 2, "hello world", (23, 42), 5]
> py> '-'.join(str(item) for item in m[1:])
> '2-hello world-(23, 42)-5'
>
>
>
> --
> Steven
>
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