Ask for help on using re

[jak]

Il 07/08/2021 04:23, Jach Feng ha scritto:
> jak 在 2021年8月6日 星期五下午4:10:05 [UTC+8] 的信中寫道：
>> Il 05/08/2021 11:40, Jach Feng ha scritto:
>>> I want to distinguish between numbers with/without a dot attached:
>>>
>>>>>> text = 'ch 1. is\nch 23. is\nch 4 is\nch 56 is\n'
>>>>>> re.compile(r'ch \d{1,}[.]').findall(text)
>>> ['ch 1.', 'ch 23.']
>>>>>> re.compile(r'ch \d{1,}[^.]').findall(text)
>>> ['ch 23', 'ch 4 ', 'ch 56 ']
>>>
>>> I can guess why the 'ch 23' appears in the second list. But how to get rid of it?
>>>
>>> --Jach
>>>
>> import re
>> t = 'ch 1. is\nch 23. is\nch 4 is\nch 56 is\n'
>> r = re.compile(r'(ch +\d+\.)|(ch +\d+)', re.M)
>>
>> res = r.findall(t)
>>
>> dot = [x[1] for x in res if x[1] != '']
>> udot = [x[0] for x in res if x[0] != '']
>>
>> print(f"dot: {dot}")
>> print(f"undot: {udot}")
>>
>> out:
>>
>> dot: ['ch 4', 'ch 56']
>> undot: ['ch 1.', 'ch 23.']
> The result can be influenced by the order of re patterns?
> 
>>>> import re
>>>> t = 'ch 1. is\nch 23. is\nch 4 is\nch 56 is\n'
>>>> re.compile(r'(ch +\d+\.)|(ch +\d+)', re.M).findall(t)
> [('ch 1.', ''), ('ch 23.', ''), ('', 'ch 4'), ('', 'ch 56')]
> 
>>>> re.compile(r'(ch +\d+)|(ch +\d+\.)', re.M).findall(t)
> [('ch 1', ''), ('ch 23', ''), ('ch 4', ''), ('ch 56', '')]
> 
> --Jach
> 
Yes, when the patterns intersect each other as in your case. the
difference between the 2 patterns is the "." in addition. The logical or
does not continue checking when the condition is satisfied, so it is a
good idea, in these cases, to search for the most complete patterns
before the others.