Python 正则表达式 - 带有 [AZ] 和 DIGITS [\\d] 的字符串

Question

import re 

 str_1 = "ABABABABABAabababaacdcdcdcd"
 str_2 = "ABABABABAB1ab2babaacdcdcdcd"
 str_3 = "123456A"
 str_4 = "123456"

 #str_3Plus_d = re.search(r'(?=.*?\d)[A-Z\d]{10,}',str_2).group(0)
 str_3Plus_d = re.search(r'(?=.*?\d)[A-Z\d]{2,4}',str_2).group(0)
 print(str_3Plus_d)

 #str_3plus_a = re.search(r'(?=.*?\d)(?=.*?[A-Z])[A-Z\d]{3,}',str_4).group(0)

 #str_3plus_both = re.search(r'(?=.*?\d)(?=.*?[A-Z])[A-Z\d]{3,}',str_4).group(0)

I am stuck with searching a STRING ([AZ] and DIGITS). I searched SO for similar Questions , here -- https://stackoverflow.com/a/28334645/4928635 , it says that (?=.*?\\d) "Checks for atleast one digit" , but that doesnt seem to be the case. As seen in -

str_3Plus_d = re.search(r'(?=.*?\d)[A-Z\d]{2,4}',str_2).group(0)
print(str_3Plus_d)

it prints me a string - which has no digits ? String it print in my JupyterNotebook is as seen below -

 ABAB

How to capture a string with - "variable number of characters and at least 2 digits and at most 4 digits , as an example - how to catch - AAABBB2223" ...

Further clarifications --

1. @pm-2ring :- the digits and alpha characters can occur in any order , the substring im trying to capture can vary in length.

2. @jean-françois-fabre :- you seem to have removed your answer - the code you gave did exactly what u said it would - thanks .

3. @clasg :- Both your comment and answer have taught me well today - im very grateful - i will revert in sometime and let you know if i would want to upvote your answer - many thanks.

Answer 1

You can do this by moving the quantification into the look-ahead and some...

^(?=(?:[^\d\n]*\d){2,4}[^\d\n]*$)[A-Z\d]*$

It's a bit more complex, but does the work, as it should.

The [^\\d\\n] matches anything but digits or newlines. Making the positive look-ahead match this construct any number of times ( * ), followed by a digit, then repeating this 2-4 times, finally followed by the non digit/LF again , makes it only match a string if it contains between 2 and 4 digits.

See it here at regex101 .