Code improvement question

[Mike Dewhirst]

On 15/11/2023 3:08 pm, MRAB via Python-list wrote:
> On 2023-11-15 03:41, Mike Dewhirst via Python-list wrote:
>> On 15/11/2023 10:25 am, MRAB via Python-list wrote:
>>> On 2023-11-14 23:14, Mike Dewhirst via Python-list wrote:
>>>> I'd like to improve the code below, which works. It feels clunky to 
>>>> me.
>>>>
>>>> I need to clean up user-uploaded files the size of which I don't 
>>>> know in
>>>> advance.
>>>>
>>>> After cleaning they might be as big as 1Mb but that would be super 
>>>> rare.
>>>> Perhaps only for testing.
>>>>
>>>> I'm extracting CAS numbers and here is the pattern xx-xx-x up to
>>>> xxxxxxx-xx-x eg., 1012300-77-4
>>>>
>>>> def remove_alpha(txt):
>>>>
>>>>       """  r'[^0-9\- ]':
>>>>
>>>>       [^...]: Match any character that is not in the specified set.
>>>>
>>>>       0-9: Match any digit.
>>>>
>>>>       \: Escape character.
>>>>
>>>>       -: Match a hyphen.
>>>>
>>>>       Space: Match a space.
>>>>
>>>>       """
>>>>
>>>>       cleaned_txt = re.sub(r'[^0-9\- ]', '', txt)
>>>>
>>>>       bits = cleaned_txt.split()
>>>>
>>>>       pieces = []
>>>>
>>>>       for bit in bits:
>>>>
>>>>           # minimum size of a CAS number is 7 so drop smaller 
>>>> clumps of digits
>>>>
>>>>           pieces.append(bit if len(bit) > 6 else "")
>>>>
>>>>       return " ".join(pieces)
>>>>
>>>>
>>>> Many thanks for any hints
>>>>
>>> Why don't you use re.findall?
>>>
>>> re.findall(r'\b[0-9]{2,7}-[0-9]{2}-[0-9]{2}\b', txt)
>>
>> I think I can see what you did there but it won't make sense to me - or
>> whoever looks at the code - in future.
>>
>> That answers your specific question. However, I am in awe of people who
>> can just "do" regular expressions and I thank you very much for what
>> would have been a monumental effort had I tried it.
>>
>> That little re.sub() came from ChatGPT and I can understand it without
>> too much effort because it came documented
>>
>> I suppose ChatGPT is the answer to this thread. Or everything. Or 
>> will be.
>>
> \b          Word boundary
> [0-9]{2,7}  2..7 digits
> -           "-"
> [0-9]{2}    2 digits
> -           "-"
> [0-9]{2}    2 digits
> \b          Word boundary
>
> The "word boundary" thing is to stop it matching where there are 
> letters or digits right next to the digits.
>
> For example, if the text contained, say, "123456789-12-1234", you 
> wouldn't want it to match because there are more than 7 digits at the 
> start and more than 2 digits at the end.
>
Thanks

I know I should invest some brainspace in re. Many years ago at a Perl 
conferenceI did buy a coffee mug completely covered with a regex cheat 
sheet. It currently holds pens and pencils on my desk. And spiders now I 
look closely!

Then I took up Python and re is different.

Maybe I'll have another look ...

Cheers

Mike

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