Modernize Lib/posixpath.py: Use startswith(), endswith(), rstrip(),

struct_passwd attributes and +=.

From SF patch #755245.

Lib/posixpath.py

@@ -45,7 +45,7 @@ def normcase(s):
 
 def isabs(s):
     """Test whether a path is absolute"""
-    return s[:1] == '/'
+    return s.startswith('/')
 
 
 # Join pathnames.
@@ -56,12 +56,12 @@ def join(a, *p):
     """Join two or more pathname components, inserting '/' as needed"""
     path = a
     for b in p:
-        if b[:1] == '/':
+        if b.startswith('/'):
             path = b
-        elif path == '' or path[-1:] == '/':
-            path = path + b
+        elif path == '' or path.endswith('/'):
+            path +=  b
         else:
-            path = path + '/' + b
+            path += '/' + b
     return path
 
 
@@ -76,8 +76,7 @@ def split(p):
     i = p.rfind('/') + 1
     head, tail = p[:i], p[i:]
     if head and head != '/'*len(head):
-        while head[-1] == '/':
-            head = head[:-1]
+        head = head.rstrip('/')
     return head, tail
 
 
@@ -129,7 +128,8 @@ def commonprefix(m):
         for i in range(len(prefix)):
             if prefix[:i+1] != item[:i+1]:
                 prefix = prefix[:i]
-                if i == 0: return ''
+                if i == 0:
+                    return ''
                 break
     return prefix
 
@@ -301,15 +301,15 @@ def walk(top, func, arg):
 def expanduser(path):
     """Expand ~ and ~user constructions.  If user or $HOME is unknown,
     do nothing."""
-    if path[:1] != '~':
+    if not path.startswith('~'):
         return path
     i, n = 1, len(path)
     while i < n and path[i] != '/':
-        i = i + 1
+        i += 1
     if i == 1:
         if not 'HOME' in os.environ:
             import pwd
-            userhome = pwd.getpwuid(os.getuid())[5]
+            userhome = pwd.getpwuid(os.getuid()).pw_dir
         else:
             userhome = os.environ['HOME']
     else:
@@ -318,8 +318,9 @@ def expanduser(path):
             pwent = pwd.getpwnam(path[1:i])
         except KeyError:
             return path
-        userhome = pwent[5]
-    if userhome[-1:] == '/': i = i + 1
+        userhome = pwent.pw_dir
+    if userhome.endswith('/'):
+        i += 1
     return userhome + path[i:]
 
 
@@ -345,13 +346,13 @@ def expandvars(path):
             break
         i, j = m.span(0)
         name = m.group(1)
-        if name[:1] == '{' and name[-1:] == '}':
+        if name.startswith('{') and name.endswith('}'):
             name = name[1:-1]
         if name in os.environ:
             tail = path[j:]
             path = path[:i] + os.environ[name]
             i = len(path)
-            path = path + tail
+            path += tail
         else:
             i = j
     return path