import re
# Match any % formatting stanza
# Any character is allowed in names, unicode names work in python 2.2+
# The name can be an empty string
safmt_pat = re.compile(r'''
% # Start with percent,
(?:\( ([^()]*) \))? # optional name in parens (do not capture parens),
[-+ #0]* # zero or more flags
(?:\*|[0-9]*) # optional minimum field width
(?:\.(?:\*|[0-9]*))? # optional dot and length modifier
[EGXcdefgiorsux%] # type code (or [formatted] percent character)
''', re.VERBOSE)
# Wrapper to allow e.g. safmt("%blah", 10, 20, spam='eggs')
# First argument must be the template
def safmt(*args, **kw):
return safmtb(args[0], args[1:], kw)
# Safe and augmented "%" string interpolation:
# - preserve % stanzas in case of missing argument or key
# - allow mixed positional and named arguments
# Note: TypeError exceptions can still happen, e.g. safmt("%d", "abc")
# Function arguments:
# template: a string containing "%" format specifiers
# args : sequence arguments for format string
# kw : mapping arguments for format string
# savepc : optionally preserve "escaped percent" stanzas
# (parameterised positional stanzas always eat args)
# verb : verbose execution, prints debug output to stdout
def safmtb(template, args=(), kw=None, savepc=0, verb=0):
if verb:
print "safmt(%r)" % (template,)
if kw is None:
kw = {}
ret = []
last = i = 0
d = {}
di = 0
pat = safmt_pat
while 1:
mo = pat.search(template, i)
if not mo:
# End of string
ret.append(template[last:])
break
i = mo.end(0)
if verb: print mo.start(), mo.group(0, 1),
stanza, name = mo.group(0, 1)
if name is not None:
# str[-1]=='x' is faster than str.endswith('x'),
# and stanza is always non-empty here so slice will never fail
if stanza[-1] == "%":
if savepc:
if verb: print 'saving stanza'
continue
# Workaround weird behaviour in python2.1-2.5: a named
# argument that is just a percent escape still raises
# KeyError, even though a positional escaped percent eats
# no args and is happy with an empty sequence.
# Workaround: provide a dummy key which never gets used.
dat = stanza % {name: None}
else:
try:
dat = stanza % kw
except KeyError:
if verb: print 'ignore missing key'
continue
if verb: print "fmt %r" % dat
else:
# %<blah>% does not use up arguments, but "%*.*%" does
numargs = stanza[-1] != "%"
if verb: print "args=%s" % numargs,
# Allow for "*" parameterisation (uses up to 2)
numargs += mo.group(0).count("*")
if verb: print "args=%s" % numargs,
p = args[di: di + numargs]
di += numargs
if verb: print "p=%s" % (p,),
if len(p) != numargs:
if verb: print "not enough pos args"
continue
if savepc and stanza[-1] == "%":
if verb: print 'saving stanza'
continue
dat = stanza % p
if verb: print "fmt %r" % dat
ret.append(template[last:mo.start()])
ret.append(dat)
last = i
return ''.join(ret)
# ****** Related Recipe ******
from ConfigParser import *
from ConfigParser import DEFAULTSECT
class SafeConfigParser(ConfigParser):
# Override get() method to use safe string interpolation
def get(self, section, option, raw=0, vars=None):
# In python2.3, the name changed from __sections to _sections
if hasattr(self, '_sections'):
sections = self._sections
defaults = self._defaults
else:
sections = self._ConfigParser__sections
defaults = self._ConfigParser__defaults
try:
sectdict = sections[section].copy()
except KeyError:
if section == DEFAULTSECT:
sectdict = {}
else:
raise NoSectionError(section)
d = defaults.copy()
d.update(sectdict)
# Update with the entry specific variables
if vars:
d.update(vars)
option = self.optionxform(option)
try:
rawval = d[option]
except KeyError:
raise NoOptionError(option, section)
if raw:
return rawval
# do the string interpolation
value = rawval # Make it a pretty variable name
for depth in range(10):
oldvalue = value
value = safmtb(value, kw=d, savepc=1)
if value == oldvalue: break
else:
raise InterpolationDepthError(option, section, rawval)
return value
