regular expression Pattern object getting converted to string if fetched from config.cfg file

Question

python file

import ConfigParser,re

config=ConfigParser.ConfigParser()
with open("temp.cfg",'r') as config_file:
    config.readfp(config_file)


x=[]
x.append(re.compile(r'abc'))
x.append((config.get("ssp",'a')).strip('"'))
print x[0]
print x[1]

config file[temp.cfg]

[ssp]
a:re.compile(r'abc')

output

>>> 
<_sre.SRE_Pattern object at 0x02110F80>
re.compile(r'abc')
>>>

What "print x[1]" should give is regular expression object but it seems to be returning string.

Looks like I am not doing it in the right way & am unable to figure it out

I don't *speak* python but to me it seems you're trying to compile an empty regex `x.append(re.compile(r''))` and that's not allowed(?) so what you're seeing is the error output. — SamWhan, Oct 20 '15 at 11:06
that's just an example ; my actual program have regular expression — Ravi Yadav, Oct 20 '15 at 11:08

hjpotter92 · Accepted Answer · 2015-10-20T11:34:43.427

2

The output of x[1] is because of the following:

x.append((config.get("ssp",'a')).strip('"'))

Since, config is the cfg file parser object, you are accessing the option a of ssp section:

[ssp]
a:re.compile(r'')

which is obviously, the string: re.compile(r'').

Using `eval`:

x.append(eval((config.get("ssp",'a')).strip('"')))

edited Oct 20 '15 at 11:34

answered Oct 20 '15 at 11:09

hjpotter92

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is there a way i can make my program understand that its a regular expression ? – Ravi Yadav Oct 20 '15 at 11:09
eval seems to be working...let me give it a try..will get back to you...thanks a lot – Ravi Yadav Oct 20 '15 at 11:13

score 0 · Answer 2 · edited May 23 '17 at 11:44

0

You need to change your config file to this:

[ssp]
a:abc

Then you can simply do (without ugly eval())

x.append(re.compile(config.get("ssp", "a")).strip())

You read the regex string first from config file and then translate it to a regex object in your code with re.compile() instead of eval(). That's also better for maintainance, because you save a lot of text in the config file (a:abc instead of a:re.compile(r'abc') for each line).

edited May 23 '17 at 11:44

Community

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1

answered Oct 20 '15 at 11:33

colidyre

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It's better not using `eval()` imho. Especially if you can avoid it. See [this](http://nedbatchelder.com/blog/201206/eval_really_is_dangerous.html) to get only an impression about using `eval()` Does my example work for you? – colidyre Oct 20 '15 at 12:14
x.append(re.compile(config.get("ssp", "a")).strip()) give different address for e.g >>> <_sre.SRE_Pattern object at 0x02310F80> <_sre.SRE_Pattern object at 0x0223AC50> – Ravi Yadav Oct 20 '15 at 12:34
That's only the address in the memory where the pattern is saved. Normally, it isn't really interesting. I don't get the relevance for it. Do you need to proof if regexes reference to same object in memory or change regex outside of Python (the latter one is not a good idea at all, for the first one you need at least two same string regexes)? – colidyre Oct 20 '15 at 12:44
More information: The output for the compiled regex (which you cannot have in a human-friendly way) is a `__repr__()`, i.e. a helpful information which have a little object information and the memory address (I'm not sure, but I think `id()` was taken internally). So this information is only relevant if you want to ensure/test object identity like _object A_ __is__ _object B_: _True_ / _False_. – colidyre Oct 20 '15 at 12:58
it wasn't working & I have other things to do so i am using eval for the time being – Ravi Yadav Oct 28 '15 at 05:22

regular expression Pattern object getting converted to string if fetched from config.cfg file

2 Answers2

Using eval:

Using `eval`: