Unable to read regex in a JSON file as a string in Python

Question

I need to read the below JSON file into Python with regex intact. I will be using the regular expressions in the program.

{
    "Title": "Sample Compliance Check",
    "Checks": {
        "6": {
            "+": ["^interfa.*", "^ip address 192\.168\.0"],
            "description": "All interfaces with IP Address 192.168.0",
            "action": "aaa new-model"
        }
    }
}

When I try to read this using the json module I get the error of invalid json.

json.decoder.JSONDecodeError: Invalid \escape:

I tried converting the backslash to double backslash

{
    "Title": "Sample Compliance Check",
    "Checks": {
        "6": {
            "+": ["^interfa.*", "^ip address 192\\.168\\.0"],
            "description": "All interfaces with IP Address 192.168.0",
            "action": "aaa new-model"
        }
    }
}

Now, it gets read in Python but I get the same output with double-backslashes.

Is there any way to encode regex in JSON and read it like it's encoded (in raw regex form)?

What you show is not valid json. Can you give an minimal working example and the traceback you are getting? — syntonym
– syntonym, Commented Jul 5, 2016 at 10:10
here is the part that's valid: { "Title": "Sample Compliance Check", "Checks": { "6": { "+": ["^interfa.*", "^ip address 192\\.168\\.0"], "description": "All interfaces with IP Address 192.168.0", "action": "aaa new-model" } } } — rahul verma
– rahul verma, Commented Jul 5, 2016 at 10:25
The string "^ip address 192\\.168\\.0" does only have single backslashes. They display as doubles so that Python can distinguish them from escape characters but it should be the regex you want ("^ip address 192\.168\.0") — SuperBiasedMan
– SuperBiasedMan, Commented Jul 5, 2016 at 10:29
@syntonym It's presumably a fragment of a larger file, but what's there is valid. — SuperBiasedMan
– SuperBiasedMan, Commented Jul 5, 2016 at 10:29
@SuperBiasedMan I thought that the problem maybe lies into how the json is read. Of course you are correct that that is (probably) a fragment of a valid json file, but in itself it is not valid json. — syntonym
– syntonym, Commented Jul 5, 2016 at 10:36

syntonym · Accepted Answer · 2016-07-05 10:38:40Z

3

Raw string formatting and "normal string formatting" in python do not change the way the string is stored, but only how you can enter the string. So the following strings are both equal:

"\\a" == r"\a"

Python shows you backslashes escaped, but if you try the regex you will see that it matches what you want to match.

>>> bool(re.match("^ip address 192\\.168\\.0", "ip address 192.168.0"))
True

answered Jul 5, 2016 at 10:38

syntonym

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3 Comments

rahul verma Over a year ago

thanks for the clarification. the string that i am getting from the json file is unicode : u'^ip address 192\\.168\\.0' So when i try to use it in the regex its not working. I think i have to decode it to utf-8, am i right ? or is there any other way ?

PM 2Ring Over a year ago

@rahulverma: Weird. You don't need to decode the regex to UTF-8, the re module handles Unicode strings correctly, even in Python 2. FWIW, bool(re.match(u"^ip address 192\\.168\\.0", "ip address 192.168.0.100")) and bool(re.match(u"^ip address 192\\.168\\.0", u"ip address 192.168.0.100")) both work properly for me on Python 2.6 and Python 3.6.

rahul verma Over a year ago

@PM2Ring: You are right ! The problem was with the regex itself. Thanks a lot.

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