varexpand: optimize access to current char

diff --git a/pym/portage/util/__init__.py b/pym/portage/util/__init__.py
index 3e7187cfdf100ec52e8ac4e8df1ad3589e2d463c..d6ac46c83ee3f1d823b2a77862da841681455ba3 100644 (file)
--- a/pym/portage/util/__init__.py
+++ b/pym/portage/util/__init__.py
@@ -660,14 +660,15 @@ def varexpand(mystring, mydict=None, error_leader=None):
        This would be a good bunch of code to port to C.
        """
        numvars=0
-       mystring=" "+mystring
        #in single, double quotes
        insing=0
        indoub=0
-       pos=1
+       pos = 0
+       length = len(mystring)
        newstring = []
-       while (pos<len(mystring)):
-               if (mystring[pos]=="'") and (mystring[pos-1]!="\\"):
+       while pos < length:
+               current = mystring[pos]
+               if current == "'":
                        if (indoub):
                                newstring.append("'")
                        else:
@@ -675,7 +676,7 @@ def varexpand(mystring, mydict=None, error_leader=None):
                                insing=not insing
                        pos=pos+1
                        continue
-               elif (mystring[pos]=='"') and (mystring[pos-1]!="\\"):
+               elif current == '"':
                        if (insing):
                                newstring.append('"')
                        else:
@@ -685,11 +686,11 @@ def varexpand(mystring, mydict=None, error_leader=None):
                        continue
                if (not insing): 
                        #expansion time
-                       if (mystring[pos]=="\n"):
+                       if current == "\n":
                                #convert newlines to spaces
                                newstring.append(" ")
-                               pos=pos+1
-                       elif (mystring[pos]=="\\"):
+                               pos += 1
+                       elif current == "\\":
                                # For backslash expansion, this function used to behave like
                                # echo -e, but that's not needed for our purposes. We want to
                                # behave like bash does when expanding a variable assignment
@@ -699,19 +700,27 @@ def varexpand(mystring, mydict=None, error_leader=None):
                                # escaped quotes here, since getconfig() uses shlex
                                # to handle that earlier.
                                if (pos+1>=len(mystring)):
-                                       newstring.append(mystring[pos])
+                                       newstring.append(current)
                                        break
                                else:
-                                       a = mystring[pos + 1]
-                                       pos = pos + 2
-                                       if a in ("\\", "$"):
-                                               newstring.append(a)
-                                       elif a == "\n":
+                                       current = mystring[pos + 1]
+                                       pos += 2
+                                       if current == "$":
+                                               newstring.append(current)
+                                       elif current == "\\":
+                                               newstring.append(current)
+                                               # BUG: This spot appears buggy, but it's intended to
+                                               # be bug-for-bug compatible with existing behavior.
+                                               if pos < length and \
+                                                       mystring[pos] in ("'", '"', "$"):
+                                                       newstring.append(mystring[pos])
+                                                       pos += 1
+                                       elif current == "\n":
                                                pass
                                        else:
                                                newstring.append(mystring[pos - 2:pos])
                                        continue
-                       elif (mystring[pos]=="$") and (mystring[pos-1]!="\\"):
+                       elif current == "$":
                                pos=pos+1
                                if mystring[pos]=="{":
                                        pos=pos+1
@@ -754,11 +763,11 @@ def varexpand(mystring, mydict=None, error_leader=None):
                                if myvarname in mydict:
                                        newstring.append(mydict[myvarname])
                        else:
-                               newstring.append(mystring[pos])
-                               pos=pos+1
+                               newstring.append(current)
+                               pos += 1
                else:
-                       newstring.append(mystring[pos])
-                       pos=pos+1
+                       newstring.append(current)
+                       pos += 1
 
        return "".join(newstring)