This discussion appears to repeat everything we already have in the PEP 275:
http://www.python.org/dev/peps/pep-0275/ FWIW, below is a real-life use case that would benefit from a switch statement or an optimization of the existing if-elif-else case. It's the unpickler inner loop of an XML pickle mechanism for Python objects. Many parser doing the usual tokenize first, then parse the tokens steps would benefit in the same way by avoiding the function call overhead. Note that you rarely have the situation where you need to have a single cases for huge ranges of values (and these can easily be handled in a separate if-else in the else branch of the switch). You do sometimes need to identical code for a few cases, so allowing multiple values per case would make such use cases have less code duplication. However, using tuple syntax for this would not be ideal, since a tuple may well be a valid value to test for. This was discussed last time around: the only way to cover this case is to always use tuple notation for the values (see the syntax example in the PEP). The code currently relies on Python interning constants that appear in code, making the 'is' test slightly faster than the '==' test. for tag in taglist: node = tag.name tagtype = tag.type if tagtype == DATA: if readdata: data = tag.tag readdata = 0 continue # This is where the switch would start... elif node is 'int': if tagtype == STARTTAG: readdata = 1 continue elif tagtype == ENDTAG: stack.append(int(data)) continue elif node is 'float': if tagtype == STARTTAG: readdata = 1 continue elif tagtype == ENDTAG: stack.append(float(data)) continue elif node is 'long': if tagtype == STARTTAG: readdata = 1 continue elif tagtype == ENDTAG: stack.append(long(data)) continue elif node is 'string': if tagtype == STARTTAG: refid = int(tag.attributes['id']) readdata = 1 continue elif tagtype == ENDTAG: data = xmlunescape(data, xmlentities) obj = data.encode('latin-1') stack.append(obj) memo[refid] = obj continue elif node is 'tuple': if tagtype == STARTTAG: refid = int(tag.attributes['id']) pushframe((node, stack, refid)) stack = [] continue elif tagtype == ENDTAG: obj = tuple(stack) node, stack, refid = popframe() memo[refid] = obj stack.append(obj) continue elif node is 'list': if tagtype == STARTTAG: refid = int(tag.attributes['id']) pushframe((node, stack, refid)) stack = [] continue elif tagtype == ENDTAG: obj = list(stack) node, stack, refid = popframe() memo[refid] = obj stack.append(obj) continue elif node is 'dict': if tagtype == STARTTAG: refid = int(tag.attributes['id']) pushframe((node, stack, refid)) stack = [] continue elif tagtype == ENDTAG: items = stack node, stack, refid = popframe() obj = {} for k,v in items: obj[k] = v memo[refid] = obj stack.append(obj) continue elif node is 'item': if tagtype == STARTTAG: continue elif tagtype == ENDTAG: key = stack[-2] value = stack[-1] stack[-2] = (key, value) del stack[-1] continue elif node is 'key' or \ node is 'value': if tagtype == STARTTAG: continue elif tagtype == ENDTAG: continue elif node is 'none': if tagtype == STARTTAG: stack.append(None) continue elif tagtype == ENDTAG: continue elif node is 'unicode': if tagtype == STARTTAG: refid = int(tag.attributes['id']) readdata = 1 continue elif tagtype == ENDTAG: data = xmlunescape(data, xmlentities) stack.append(obj) memo[refid] = obj continue elif node is 'ref': if tagtype == STARTTAG: readdata = 1 continue elif tagtype == ENDTAG: stack.append(memo[int(data)]) continue elif node is 'instance': if tagtype == STARTTAG: attr = tag.attributes refid = int(attr['id']) classname = str(attr['class']) #print 'instance:', repr(refid), repr(classname) pushframe((node, stack, refid, classname)) stack = [] continue elif tagtype == ENDTAG: initargs, state = stack node, stack, refid, classname = popframe() obj = self.create_instance(classname, initargs, state) memo[refid] = obj stack.append(obj) continue elif node is 'initArgs': if tagtype == STARTTAG: pushframe((node, stack)) stack = [] continue elif tagtype == ENDTAG: obj = tuple(stack) node, stack = popframe() stack.append(obj) continue elif node is 'dynamic': if tagtype == STARTTAG: attr = tag.attributes refid = int(attr['id']) pushframe((node, stack, refid)) stack = [] continue elif tagtype == ENDTAG: callable, args = stack[:2] if len(stack) >= 3: state = stack[2] else: state = None node, stack, refid = popframe() obj = self.create_object(callable, args, state) memo[refid] = obj stack.append(obj) continue elif node is 'state' or \ node is 'callable' or \ node is 'args' or \ node is 'imag' or \ node is 'real': if tagtype in (STARTTAG, ENDTAG): continue elif node is 'global': if tagtype == STARTTAG: attr = tag.attributes refid = int(attr['id']) fullname = attr['name'] obj = self.find_global(fullname) memo[refid] = obj stack.append(obj) continue elif tagtype == ENDTAG: continue elif node is 'complex': if tagtype == STARTTAG: continue elif tagtype == ENDTAG: real, imag = stack[-2:] stack[-2] = complex(imag, real) del stack[-1] continue elif node is 'xmlPickle': if tagtype == STARTTAG: stack = [] continue elif tagtype == ENDTAG: obj = stack[-1] break # If we get here, something is wrong raise UnpicklingError, \ 'unrecognized input data: tag %s' % tag.tag -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Jun 20 2006) >>> Python/Zope Consulting and Support ... http://www.egenix.com/ >>> mxODBC.Zope.Database.Adapter ... http://zope.egenix.com/ >>> mxODBC, mxDateTime, mxTextTools ... http://python.egenix.com/ ________________________________________________________________________ 2006-07-03: EuroPython 2006, CERN, Switzerland 12 days left ::: Try mxODBC.Zope.DA for Windows,Linux,Solaris,FreeBSD for free ! :::: _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
