[Tutor] escape character regex

[Ian D]

Ok I got it. 

pchars = re.compile(b'\x00\x00\x00[\0-\xff]')

preceeding b and [0-\xff]





----------------------------------------
> From: duxbuz at hotmail.com
> To: tutor at python.org
> Date: Sun, 29 Mar 2015 07:55:01 +0000
> Subject: Re: [Tutor] escape character regex
>
> Ha ha thanks Danny for the hex message!
>
>
> I am looking to basically match 2 unknown hex values or a byte at the end of the 4 byte sequence.
>
> I realise now I am trying to use a numeric \d expression when it needs to be matching 2 nibbles or a byte.
>
>
> Is there a way to match using some sort of wildcard for the last byte as it changes?
>
>
> Thanks
>
> ----------------------------------------
>> Date: Sat, 28 Mar 2015 20:21:09 -0400
>> From: davea at davea.name
>> To: tutor at python.org
>> Subject: Re: [Tutor] escape character regex
>>
>> On 03/28/2015 03:37 PM, Ian D wrote:
>>> Hi
>>>
>>>
>>> I run a regex like this:
>>>
>>>> pchars = re.compile('\x00\x00\x00') &with or without 'r' for raw
>>
>> Which one did you actually want? The 3 byte sequence consisting of
>> nulls, or the 12 byte one containing zeroes and backslashes? I'm going
>> to assume the former, in which case you cannot use 'r' for raw. Unless
>> you've got a null key on your keyboard.
>>
>>>
>>> on a string like this:
>>>
>>>> data = "['broadcast', 'd8on\x00\x00\x00\x11broadcast', 'd11on']"
>>>
>>>> print "found pchars :",pchars.findall(data)
>>>
>>> which returns:
>>>
>>>> found pchars : ['\x00\x00\x00']
>>>
>>>
>>> But if I try to match the extra digits at the end like this:
>>>
>>>> pchars = re.compile('\x00\x00\x00\x\d+')
>>>
>>> I get an error:
>>>
>>>> ValueError: invalid \x escape
>>
>> The \x escape sequence must be followed by exactly two hex digits, and
>> forms a single byte from them. What did you want that byte to be, and
>> why didn't you specify it?
>>
>>>
>>> Or if I use another ide than idle it actually flags it as an "illegal hexadecimal escape sequence"
>>>
>>
>> The question is not what the various IDE's produce, but what the Python
>> compiler produces. So once you started getting errors, you really
>> should have just run it in the interactive interpreter, without IDE's
>> second-guessing you. Anyway, in 2.7.6's interactive interpreter, I get:
>>
>>>>> a = '\x00\x00\x00\x\d+'
>> ValueError: invalid \x escape
>>>>>
>>
>> So it has nothing to do with re, and is simply the result of trying an
>> invalid string literal.
>>
>> What string were you hoping to get? You mention you wanted to match
>> digits at the end (end of what?). Perhaps you wanted a real backslash
>> followed by the letter d. In that case, since you cannot use a raw
>> string (see my first response paragraph), you need to double the backslash.
>>
>>>>> a = '\x00\x00\x00\\d+'
>>>>> print a
>> \d+
>>
>>
>> Your data is funny, too, since it almost looks like it might be a string
>> representation of a Python list. But assuming you meant it exactly like
>> it is, there is a funny control character following the nulls.
>>>
>>> How could I match the \x00\x00\x00\x11 portion of the string?
>>>
>>
>> There are no digits in that portion of the string, so I'm not sure why
>> you were earlier trying to match digits.
>>
>> Perhaps you meant you were trying to match the single control character
>> x'11'. In that case, you'd want
>>
>> a = '\x00\x00\x00\x11'
>> pchars = re.compile(a)
>>
>>
>> But if you wanted to match an arbitrary character following the nulls,
>> you'd want something different.
>>
>> I think you'd better supply several strings to match against, and show
>> which ones you'd expect a match for.
>>
>> --
>> DaveA
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