Code improvement question

[MRAB]

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.