Velocity Reviews - best way to read a configuration file

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best way to read a configuration file

Hi All,

i am wondering about the best way to read in a configuration file that
goes like:

###########

[users]
source_dir = '/home/karthik/Projects/python'
data_dir = '/home/karthik/Projects/data'
result_dir = '/home/karthik/Projects/Results'
param_file = $result_dir/param_file
res_file = $result_dir/result_file
comment = 'this is a comment'

K = 8
simulate_K = 0

N = 4000
mod_scheme = 'QPSK'

Na = K+2

######################

As of now i use config parser and i get this in a dictionary but

a) but i have users.na and not users.Na (all the fields are in lower
case)

b) all the rhs arguements are string, but i have handled this by
trying " try eval(rhs) ... except ..." block

c) Na = 'K+2' though does not work, would like to have Na = 10, but i
get users.na = 'K+2'

d) result_file, param_file should actually be should be with pathname
extensions filled in.

Have looked in c.l.py none one ofthe suggestions was to use
splitlines, this cant handle blank lines, other was to have config.py
...

Hope to get some solution for this ..

with warm regards

karthik

--

-----------------------------------------------------------------------
Karthikesh Raju, email: karthik@james.hut.fi
Researcher, http://www.cis.hut.fi/karthik
Helsinki University of Technology, Tel: +358-9-451 5389
Laboratory of Comp. & Info. Sc., Fax: +358-9-451 3277
Department of Computer Sc.,
P.O Box 5400, FIN 02015 HUT,
Espoo, FINLAND
-----------------------------------------------------------------------

Re: best way to read a configuration file

"Karthikesh Raju" <karthik@james.hut.fi> wrote in message
news:2dy8qimiwq.fsf@itl-pc87.hut.fi...
>
> Hi All,
>
> i am wondering about the best way to read in a configuration file that
> goes like:
>
> ###########
>
> [users]
> source_dir = '/home/karthik/Projects/python'
> data_dir = '/home/karthik/Projects/data'
> result_dir = '/home/karthik/Projects/Results'
> param_file = $result_dir/param_file
> res_file = $result_dir/result_file
> comment = 'this is a comment'
>
> K = 8
> simulate_K = 0
>
> N = 4000
> mod_scheme = 'QPSK'
>
> Na = K+2
>
> ######################
>
> As of now i use config parser and i get this in a dictionary but
>
> a) but i have users.na and not users.Na (all the fields are in lower
> case)
>
> b) all the rhs arguements are string, but i have handled this by
> trying " try eval(rhs) ... except ..." block
>
> c) Na = 'K+2' though does not work, would like to have Na = 10, but i
> get users.na = 'K+2'
>
> d) result_file, param_file should actually be should be with pathname
> extensions filled in.
>
> Have looked in c.l.py none one ofthe suggestions was to use
> splitlines, this cant handle blank lines, other was to have config.py
> ..
>
> Hope to get some solution for this ..
>
> with warm regards
>
> karthik
>
>
> --
>
> -----------------------------------------------------------------------
> Karthikesh Raju, email: karthik@james.hut.fi
> Researcher, http://www.cis.hut.fi/karthik
> Helsinki University of Technology, Tel: +358-9-451 5389
> Laboratory of Comp. & Info. Sc., Fax: +358-9-451 3277
> Department of Computer Sc.,
> P.O Box 5400, FIN 02015 HUT,
> Espoo, FINLAND
> -----------------------------------------------------------------------

I modified the config parser that is included as an example that ships with
pyparsing, by adding:

iniLines = "\n".join( file("karthik.ini").readlines() )
config = inifile_BNF().parseString(iniLines)
pprint.pprint( config.asList() )
for k in config.users.keys():
print k,":",config.users[k]

This gives the following output:

[['users',
['source_dir ', " '/home/karthik/Projects/python'"],
['data_dir ', " '/home/karthik/Projects/data'"],
['result_dir ', " '/home/karthik/Projects/Results'"],
['param_file ', ' $result_dir/param_file'],
['res_file ', ' $result_dir/result_file'],
['comment ', " 'this is a comment'"],
['K ', ' 8'],
['simulate_K ', ' 0'],
['N ', ' 4000'],
['mod_scheme ', " 'QPSK'"],
['Na ', ' K+2']]]
comment : 'this is a comment'
data_dir : '/home/karthik/Projects/data'
mod_scheme : 'QPSK'
Na : K+2
K : 8
simulate_K : 0
N : 4000
res_file : $result_dir/result_file
result_dir : '/home/karthik/Projects/Results'
source_dir : '/home/karthik/Projects/python'
param_file : $result_dir/param_file

This actually shows the 3 access modes to the results from a pyparsing
parseString() operation:
- as a raw list of tokens (optionally grouped into sublists, giving a parse
tree)
- as an object with attributes (note reference to 'config.users', also
notice that keys are not converted to lower case)
- as a dictionary (access to config.users[k] for each key k)

The 2nd level keys could also be referenced using the form
config.users.data_dir, config.users.comment, etc.

pyparsing also comes with an expression parser and evaluator in its
examples. With some creative merging of the two, I think you could in
fairly short order have a config parser that would handle your Na = K+2 and
res_file = "$result_dir..." config values.

The pyparsing home page is at http://pyparsing.sourceforge.net.

HTH,
-- Paul

Re: best way to read a configuration file

Sorry about that last null post, my fingers tripped over the send button
before I started typing my response.

-- Paul

Re: best way to read a configuration file

Thankx paul, will have to download pyparsing, will do in a short will
and try your trick, hope it works well :-)

With warm regards

karthik
--

-----------------------------------------------------------------------
Karthikesh Raju, email: karthik@james.hut.fi
Researcher, http://www.cis.hut.fi/karthik
Helsinki University of Technology, Tel: +358-9-451 5389
Laboratory of Comp. & Info. Sc., Fax: +358-9-451 3277
Department of Computer Sc.,
P.O Box 5400, FIN 02015 HUT,
Espoo, FINLAND
-----------------------------------------------------------------------

Re: best way to read a configuration file

I kept this sample from an ealier thread or website. I don't have the
link nor can I give credit to the author. If you have some lattitude
on the exact format of the config file, this may do the trick for you
though:

Python App Macro Lang

class App:
def __init__(self, name):
self._name = name
def name(self):
return self._name

i=123

macrosource = """
print app.name()
i=1
if i==2:
server="internal.blah.com"
else:
server="external.blah.com"

"""

code = compile(macrosource, '<string>', "exec")
anApp = App('Global App Object')
context = {}

# populate context with fun things
context["app"] = anApp
exec code in context

print "The server is:" + context["server"]
if i != 123:
raise "local variable 'i' changed"

output = """
c:\cygwin\bin\sh -c "python PyAsMacroLang.py"
Global App Object
The server is:external.blah.com
"""