Unable to parse string using python match() - getting error AttributeError: 'NoneType' object has no attribute 'group'

Question

I have a dictionary which is output of an aerospike info command. I need to parse a value from it.

I have set it as a string to the response variable as shown below. However, it's type still shows as dictionary. So, as suggested in this answer, I have dumped it to string type and then tried to call match() (because it expects string parameter). However, I am still getting this error.

respone = "{'BB912E94CDE0B0E': (None, 'n_objects=179:n-bytes-memory=0:stop-writes-count=0:set-enable-xdr=use-default:disable-eviction=true:set-delete=false;\n')}"
p = "/.*\'n_objects=([0-9]+)\:.*/gm"
stringResponse = json.dumps(response)
print type(response)
print stringResponse
print type(stringResponse)
print re.match(p,stringResponse).group(1)

Output -

<type 'dict'>
{"BB912E94CDE0B0E": [null, "n_objects=179:n-bytes-memory=0:stop-writes-count=0:set-enable-xdr=use-default:disable-eviction=true:set-delete=false;\n"]}
<type 'str'>
Traceback (most recent call last):
  File "Sandeepan-oauth_token_cache_complete_sanity_cp.py", line 104, in <module>
    print re.match(p,stringResponse).group(1)
AttributeError: 'NoneType' object has no attribute 'group'

I am getting the desired output using the same string and regex pattern - https://regex101.com/r/ymotqe/1

the variable respone in the first line isn't used anywhere — n8sty
– n8sty, Commented Jul 29, 2018 at 19:51

Patrick Artner · Accepted Answer · 2018-07-29 19:55:46Z

2

You need to correct your pattern. The /gm part at the end corresponds to flags for regex. Some other things '/' are also not needed.

import json
import re

# fixed variable name
response = "{'BB912E94CDE0B0E': (None, 'n_objects=179:n-bytes-memory=0:stop-writes-count=0:set-enable-xdr=use-default:disable-eviction=true:set-delete=false;\n')}"

# fixed pattern
p = ".*'n_objects=([0-9]+):.*"
stringResponse = json.dumps(response)
print stringResponse
print type(response)

# fixed flags parameter (but you do not need it in your example)
print re.match(p,stringResponse, flags=re.M).group(1)

Output:

"{'BB912E94CDE0B0E': (None, 'n_objects=179:n-bytes-memory=0:stop-writes-count=0:set-enable-xdr=use-default:disable-eviction=true:set-delete=false;\n')}"
<type 'str'>
179

When using regex101.com you should also switch to python mode.

edited Jul 29, 2018 at 19:55

answered Jul 29, 2018 at 19:50

Patrick Artner

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2 Comments

tripleee Over a year ago

The leading slash is apparently also part of the misunderstanding here.The regex should probably simply start with r"'n_objects unless the example is wrong and the OP really needs to make sure they get the last one out of a string with multiple possible matches. (Single quote is not a metacharacter in this context, so doesn't need a backslash escape.)

tripleee Over a year ago

Still the leading .* is probably redundant, though if you take it out, you need to switch to re.search() instead of re.match().

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