"NoneType" error message for variables of class string type

Question

I understand that re.search returns a match object re.search(pattern, string, flags=0) I am testing the success of the match & then retrieving the string.

# matchTest.py --- testing match object returns

import re

# expected_pattern = suburbRegex
suburbRegex = "(?s)(,_\S+\s)"
# line leading up to and including expected_pattern
mostOfLineRex = "(?s)(^.+,\S+)"
# expected_pattern to end of line
theRestRex = "(?s),_\S+\s\w+\s(.+)"

fileLines = ['173 ANDREWS John Frances 20 Bell_Road,_Sub_urbia Semi Retired\n']

for fileLine in fileLines:
    
    result = re.search(suburbRegex, fileLine)
    # print(type(result)) # re.Match
    if(result):
        patResult = re.search(suburbRegex, fileLine).group(0)
        # print(patResult)
        # print(type(patResult)) # str
        # print(type(re.search(suburbRegex, fileLine).group(0))) # str

        start = re.search(mostOfLineRex, fileLine)
        if(start):
            start = re.search(mostOfLineRex, fileLine).group(0)
            # print(start)
            print(type(start)) # str
        end = re.search(theRestRex, fileLine)
        if(end):
            end = re.search(theRestRex, fileLine).group(0)
            # print(end)
            print(type(end)) # str
        
        newFileLine = start + ' ' + end 
    else:
        print("The listing does not have a suburb!")

# File "~\matchTest.py", line 31, in <module>
#    newFileLine = start + ' ' + end
# TypeError: can only concatenate str (not "NoneType") to str

I checked that types for start & end are <class 'str'> So why do I get NoneType error?

That line in the error is still outside the result checks. Print the checks right before that line — Mark Tolonen
– Mark Tolonen, Commented Dec 18, 2022 at 1:38
In your code the type check for 'start' occurs only if 'start' is 'True', that is - not 'None'. And the type check for 'end' occurs only if 'end' is True, that is - not 'None'. — Иван Балван
– Иван Балван, Commented Dec 18, 2022 at 7:33

Adam Smooch · Accepted Answer · 2022-12-18 01:42:36Z

1

You have an erroneous assumption about the return values from re.search()

>>> matches = re.search(r'[0-9]+', "testme 9"); matches; type(matches)
<re.Match object; span=(7, 8), match='9'>
<class 're.Match'>
>>> matches = re.search(r'[0-9]+', "testme"); matches; type(matches)
<class 'NoneType'>

Which explains your error when trying to concatenate start " " and end.

answered Dec 18, 2022 at 1:42

Adam Smooch

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1 Comment

Dave Over a year ago

Thanks all. Am new to Python. I now see NoneType as a useful error hint.

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