Page MenuHomeHEPForge
Files F10882029

lorentzparser.py
No OneTemporary
Actions

lorentzparser.py
View Options

"""
AST visitor class to extract left / right couplings from Lorentz structures
"""
import ast
def parse_lorentz(expr):
result = LorentzParser().parse(expr)
return result
class LorentzParserException(Exception):
"""Base class for all LorentzParser exceptions."""
def cleaner(text):
"""Convert LorentzParser output to a (left,right) tuple of prefactors"""
if 'm' in text and 'p' in text:
raise LorentzParserException('Both projections in one term: %s' % text)
if text in [['g'],['i']]:
return (1,1)
else:
try:
text.remove('g')
except ValueError:
pass
try:
text.remove('i')
except ValueError:
pass
def helper(text,char):
text.remove(char)
try:
return int(''.join(text))
except ValueError:
text.append('1')
return int(''.join(text))
left, right = 0, 0
if 'm' in text:
left = helper(text,'m')
elif 'p' in text:
right = helper(text,'p')
elif 'y' in text:
val = helper(text,'y')
left = -val
right = val
return (left,right)
class LorentzParser(ast.NodeVisitor):
"""Convert UFO Lorentz structures to left / right couplings
This parser is very sensitive to changes in the way UFO Lorentz
structures are written out.
"""
def parse(self,expression):
self.result = [[]]
tree = ast.parse(expression)
#print '---\n',ast.dump(tree),'\n---'
cleaned = map(cleaner,self.visit(tree))
return reduce(lambda a,b: (a[0]+b[0], a[1]+b[1]), cleaned)
##################################
def newterm(self):
self.result.append([])
def add(self,a):
self.result[-1].append(a)
##################################
def visit_Module(self,node):
self.generic_visit(node)
return self.result
def generic_visit(self,node):
typename = type(node).__name__
harmless = ['Module','Expr','BinOp','Mult']
if typename not in harmless:
raise LorentzParserException('Missing implementation for %s' % typename)
super(LorentzParser,self).generic_visit(node)
def visit_Call(self,node):
subs = {
'Gamma' : 'g',
'Gamma5' : 'y',
'Identity' : 'i',
'ProjM' : 'm',
'ProjP' : 'p',
}
try:
self.add(subs[node.func.id])
except KeyError:
err = "Unknown lorentz component %s" % node.func.id
raise LorentzParserException(err)
def visit_Num(self,node):
self.add(str(node.n))
def visit_Sub(self,node):
self.newterm()
self.add('-')
def visit_Add(self,node):
self.newterm()

File Metadata

Mime Type
text/plain
Expires
Sat, May 3, 7:01 AM (6 h, 50 m)
Storage Engine
blob
Storage Format
Raw Data
Storage Handle
4983249
Default Alt Text
lorentzparser.py (2 KB)

Event Timeline