AttributeError：'NoneType'对象没有属性'group'

Question

I have to assimilate some data. The scripts already exist but need to be adjusted to the new data.

So there is a line:

head = fn.replace(re.search(r'\d{8}_\d{4}', fn).group(),'')

where I get the Error: AttributeError: 'NoneType' object has no attribute 'group'

To fix this I need to understand whats actually is going on at this line.
And I do not understand what is done after the "replace". Can someone explain me whats going on here? What does r'\\d{8}_\\d{4}' mean?

Answer 1

re.search is finding matches of your regex pattern and returns a regex match object. If there are no matches it returns None. So You can't call .group() on None.

In [38]: re.search(r'921', mystr)
Out[38]: <_sre.SRE_Match object; span=(23, 26), match='921'>

In [39]: mystr
Out[39]: "b'la lala 135\\r\\n 1039 921\\r\\n'"

In [40]: re.search(r'921', mystr)
Out[40]: <_sre.SRE_Match object; span=(23, 26), match='921'>

In [41]: re.search(r'potatoes', mystr)

The SRE_Match object has the group() method which gets the string value of the match.

In [42]: re.search(r'921', mystr).group()
Out[42]: '921'

So, if you're still not clear what it's all doing, it's finding the string fn that matches the regex pattern provided in re.search() and removes it from the string fn by replacing it with '' . In this case it's finding matches in fn that have 8 digits( \\d{8} ) followed by an underscore and then 4 more digits( \\d{4} ). so strings that look like 12345678_1234 .