Python或正则表达式中，非空结果

Question

I need to find a substring that can take 2 different forms:

>>> test = '348249432'
>>> x = re.findall("([2][0][0-9]{7})|([3][0-9]{8})", test)
>>> x
[('', '348249432')]

How can I ask Python not to return empty string, and to only give me result where a matching could have been done ?

Answer 1

findall returns the captured groups, stated in the documentation :

If one or more groups are present in the pattern, return a list of groups; this will be a list of tuples if the pattern has more than one group. Empty matches are included in the result unless they touch the beginning of another match .

You want to use alternation inside of one capturing group, and I would write this as:

>>> test = '348249432'
>>> re.findall("(20[0-9]{7}|3[0-9]{8})", test)
['348249432']