diff --git a/Lib/shlex.py b/Lib/shlex.py
index de9b974..2d7d68a 100644
--- a/Lib/shlex.py
+++ b/Lib/shlex.py
@@ -1,14 +1,14 @@
 """A lexical analyzer class for simple shell-like syntaxes."""
 
-# Module and documentation by Eric S. Raymond, 21 Dec 1998
+# Module and documentation by Eric S. Raymond, 21 Dec 1998 
 # Input stacking and error message cleanup added by ESR, March 2000
+# push_source() and pop_source() made explicit by ESR, January 2001. 
 
 import os.path
 import sys
 
-
 class shlex:
-    "A lexical analyzer class for simple shell-like syntaxes."
+    "A lexical analyzer class for simple shell-like syntaxes." 
     def __init__(self, instream=None, infile=None):
         if instream:
             self.instream = instream
@@ -38,6 +38,28 @@
             print "shlex: pushing token " + `tok`
         self.pushback = [tok] + self.pushback
 
+    def push_source(self, newstream, newfile=None):
+        "Push an input source onto the lexer's input source stack."
+        self.filestack.insert(0, (self.infile, self.instream, self.lineno))
+        self.infile = newfile
+        self.instream = newstream
+        self.lineno = 1
+        if self.debug:
+            if newfile:
+                print 'shlex: pushing to file %s' % (self.infile,)
+            else:
+                print 'shlex: pushing to stream %s' % (self.instream,)
+
+    def pop_source(self):
+        "Pop the input source stack."
+        self.instream.close()
+        (self.infile, self.instream, self.lineno) = self.filestack[0]
+        self.filestack = self.filestack[1:]
+        if self.debug:
+            print 'shlex: popping to %s, line %d' \
+                  % (self.instream, self.lineno)
+        self.state = ' '
+
     def get_token(self):
         "Get a token from the input stream (or from stack if it's nonempty)"
         if self.pushback:
@@ -50,26 +72,17 @@
         raw = self.read_token()
         # Handle inclusions
         while raw == self.source:
-            (newfile, newstream) = self.sourcehook(self.read_token())
-            self.filestack.insert(0, (self.infile, self.instream, self.lineno))
-            self.infile = newfile
-            self.instream = newstream
-            self.lineno = 1
-            if self.debug:
-                print 'shlex: pushing to file %s' % (self.infile,)
+            spec = self.sourcehook(self.read_token())
+            if spec:
+                (newfile, newstream) = spec
+                self.push_source(newstream, newfile)
             raw = self.get_token()
         # Maybe we got EOF instead?
         while raw == "":
             if len(self.filestack) == 0:
                 return ""
             else:
-                self.instream.close()
-                (self.infile, self.instream, self.lineno) = self.filestack[0]
-                self.filestack = self.filestack[1:]
-                if self.debug:
-                    print 'shlex: popping to %s, line %d' \
-                          % (self.instream, self.lineno)
-                self.state = ' '
+                self.pop_source()
                 raw = self.get_token()
          # Neither inclusion nor EOF
         if self.debug >= 1:
@@ -88,13 +101,13 @@
                 self.lineno = self.lineno + 1
             if self.debug >= 3:
                 print "shlex: in state", repr(self.state), \
-                      "I see character:", repr(nextchar)
+                      "I see character:", repr(nextchar) 
             if self.state is None:
-                self.token = ''         # past end of file
+                self.token = ''        # past end of file
                 break
             elif self.state == ' ':
                 if not nextchar:
-                    self.state = None   # end of file
+                    self.state = None  # end of file
                     break
                 elif nextchar in self.whitespace:
                     if self.debug >= 2:
@@ -123,14 +136,14 @@
                 if nextchar == self.state:
                     self.state = ' '
                     break
-                elif not nextchar:      # end of file
+                elif not nextchar:	# end of file
                     if self.debug >= 2:
                         print "shlex: I see EOF in quotes state"
                     # XXX what error should be raised here?
                     raise ValueError, "No closing quotation"
             elif self.state == 'a':
                 if not nextchar:
-                    self.state = None   # end of file
+                    self.state = None	# end of file
                     break
                 elif nextchar in self.whitespace:
                     if self.debug >= 2:
@@ -181,7 +194,7 @@
         return "\"%s\", line %d: " % (infile, lineno)
 
 
-if __name__ == '__main__':
+if __name__ == '__main__': 
     if len(sys.argv) == 1:
         lexer = shlex()
     else: