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vsajip/pct2fmt.py

CreatedOctober 3, 2009 22:25

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pct2fmt.py

	#
	# Copyright (C) 2009 Vinay Sajip.
	# Licensed under the PSF licence.
	# Exploratory code to convert %-format strings to {}-format.
	#

	importre

	PATTERN=re.compile(r'''
	% # specifier start
	(\((?P<key>[^)]+)\))? # optional mapping key
	(?P<flags>[#+0 -]*) # conversion flags
	(?P<min_width>(\\|([1-9][0-9])))? # minimum width
	(\.(?P<precision>(\\|([1-9][0-9]))))? # precision
	(?P<len_modifier>[hlL])? # length modifier
	(?P<conversion>[diouxXeEfFgGcrs%]) # conversion
	''',re.VERBOSE)

	classPercentConversion:
	'''Represents a single conversion group.'''

	def__init__(self,converter,match):
	'''
	Initialize using the regex match information.

	The converter is passed because we need to keep track of the
	positional argument index, so that we can support minimum width
	and precision values of '*'.
	'''

	self.source=match.group(0)
	d=match.groupdict()
	self.span=match.span()
	s=d['key']
	ifsisNone:
	self.key=converter.next_index()
	else:
	self.key=s
	s=d['min_width']
	ifs=='*':
	#TODO {} representation is hard-wired, could generalise this
	#if needed.
	self.min_width='{%s}'%converter.next_index()
	else:
	self.min_width=s
	s=d['precision']
	ifs=='*':
	self.precision='{%s}'%converter.next_index()
	else:
	self.precision=s
	#len_modifier not used
	#self.len_modifier = d['len_modifier']
	self.flags=d['flags']
	self.conversion=d['conversion']

	defas_brace(self):
	'''Return representation of this conversion group for {}-formatting.'''

	#TODO: '#', ' ' flags not handled
	conversion=self.conversion
	ifconversion=='%':
	result='%'
	else:
	key=self.key
	flags=self.flags
	ifself.min_widthisNone:
	align=''
	elif'-'inflags:
	align=''# could use '<', but as it's the default...
	elif'0'inflagsandconversionin'diouxX':
	align='='
	else:
	align='>'
	sign=''
	if'+'inflags:
	sign='+'
	elif' 'inflags:
	sign=' '
	alt=''
	fill=''
	if'0'inflagsand'-'notinflagsandconversionnotin'crs':
	fill='0'
	if'#'inflagsandconversionin'diuxX':# exclude 'o'
	alt='#'
	transform=''
	ifconversionin'iu':
	conversion='d'
	#%s is interpreted as calling str() on the operand, so
	#we specify !s in the {}-format. If we don't do this, then
	#we can't convert the case where %s is used to print e.g. integers
	#or floats.
	elifconversionin'rs':
	transform='!'+conversion
	conversion=''
	prefix='%s%s'% (key,transform)
	suffix='%s%s%s%s'% (fill,align,sign,alt)
	ifself.min_width:
	suffix+=self.min_width
	ifself.precision:
	suffix+='.'+self.precision
	suffix+=conversion
	result=prefix
	ifsuffix:
	result+=':'+suffix
	result='{%s}'%result
	returnresult

	classPercentToBraceConverter:
	'''Utility class to convert a %-format string to a {}-format string.'''

	def__init__(self,percent_format):
	self.initial=percent_format
	self.argindex=0

	defnext_index(self):
	'''Get the next argument index.'''
	result='%d'%self.argindex
	self.argindex+=1
	returnresult

	defconvert(self):
	'''Perform the conversion, and return its result.'''
	s=self.initial.replace('{','{{').replace('}','}}')
	result= [cforcins]# convert to mutable form
	matches= [mforminPATTERN.finditer(s)]
	conversions= []
	ifmatches:
	forminmatches:
	conversions.append(PercentConversion(self,m))
	#Go backwards so that span values remain valid as we go
	forconvinreversed(conversions):
	s,e=conv.span
	result[s:e]=conv.as_brace()
	return''.join(result),conversions

	defmain():
	'''Quick-n-dirty test harness for PercentToBraceConverter.'''
	importsys
	fromrandomimportchoice
	ifsys.version_info[0]==3:
	get_str=input
	else:
	get_str=raw_input

	classDummy:
	def__str__(self):
	return"I'm a dummy at %#x"%id(self)

	INSTANCE_VALUE=Dummy()
	INTEGER_VALUE=0x1234
	NEGATIVE_VALUE=-0x5678
	FLOAT_VALUE=3.14159265358979323846
	LARGE_FLOAT_VALUE=31415926535323846e108
	NEGATIVE_FLOAT_VALUE=-2.71828182845904523536
	LARGE_NEGATIVE_FLOAT_VALUE=-271828182845904523536e108

	INT_VALUES= (INTEGER_VALUE,NEGATIVE_VALUE)
	FLOAT_VALUES= (FLOAT_VALUE,NEGATIVE_FLOAT_VALUE,LARGE_FLOAT_VALUE,LARGE_NEGATIVE_FLOAT_VALUE)

	STRING_VALUE='abcd'
	STRING_VALUES= (INTEGER_VALUE,NEGATIVE_VALUE,FLOAT_VALUE,LARGE_FLOAT_VALUE,NEGATIVE_FLOAT_VALUE,LARGE_NEGATIVE_FLOAT_VALUE,STRING_VALUE,INSTANCE_VALUE)

	VALUE_MAP= {
	'd' :INT_VALUES,
	'i' :INT_VALUES,
	'o' :INT_VALUES,
	'u' :INT_VALUES,
	'x' :INT_VALUES,
	'X' :INT_VALUES,
	'e' :FLOAT_VALUES,
	'E' :FLOAT_VALUES,
	'f' :FLOAT_VALUES,
	'F' :FLOAT_VALUES,
	'g' :FLOAT_VALUES,
	'G' :FLOAT_VALUES,
	'c' : (INTEGER_VALUE,),
	'r' :STRING_VALUES,
	's' :STRING_VALUES,
	}
	whileTrue:
	s=get_str("Enter a %-format string:")
	ifnots:
	break
	f,conversions=PercentToBraceConverter(s).convert()
	print('%s -> %s'% (s,f))
	ifconversions:
	values= []
	forcinconversions:
	vals=VALUE_MAP.get(c.conversion,None)
	ifvals:
	values.append(choice(vals))
	values=tuple(values)
	print("%-20s: %s"% ('Example raw values',', '.join([repr(v)forvinvalues])))
	print("%-20s: %s"% ('Output using %',s%values))
	print("%-20s: %s"% ('Output using {}',f.format(*values)))

	if__name__=="__main__":
	main()

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