Replacing values in formated file with python

Question

I have a string see attached file like that and i would like to modify it using a function

Giving section name parameter name and value to set

Also in case i want to modify several parameters for a same section how can i have position in file to avoid scanning x time for a same section :

&NAM_WRITE_COVER_TEX CLANG='FR'
/
&NAM_FRAC LECOCLIMAP = T
/
&NAM_PGD_GRID PGRID = 'CONF PROJ '
/
&NAM_CONF_PROJ_GRID 
XLATCEN=43.,
XLONCEN=0.
NIMAX=12, 
NJMAX=8, 
XDX=60000., 
XDY=60000. /
&NAM_CONF_PROJ 
XLAT0=43., XLON0=0., XRPK=1.0, XBETA=0. /
/
&NAM_PGD_SCHEMES CNATURE = 'ISBA' , 
CSEA = 'SEAFLX' , 
CTOWN = 'TEB' , 
CWATER = 'WATFLX' ,
LGARDEN = F
/

Answer 1

I could suggest using python regular expressions. http://docs.python.org/2/library/re.html . The regular expression will only use one pass.

def replace_value(matchobj):
    new_repl_dict = {'XLATCEN': 54, 'XDX': 7000, 'CTOWN': "'NEW_VAL'"}
    if matchobj.group(1) in new_repl_dict: 
        return matchobj.group(1) + matchobj.group(2) + new_repl_dict[matchobj.group(1)]

file = "&NAM_WRITE_COVER_TEX CLANG='FR'\n..."
re.sub('(XLATCEN|XDX|CTOWN)(\s*=\s*)([^\n]*)', replace_value, file)