updated python version verification so it doesn't break on future python 4 release

Author: Streppel

memory_profiler.py

@@ -31,15 +31,15 @@
     line_cell_magic = lambda func: func
     magics_class = lambda cls: cls
 
-PY3 = sys.version_info[0] == 3
+PY2 = sys.version_info[0] == 2
 
 _TWO_20 = float(2 ** 20)
 
-if PY3:
+if PY2:
+    import __builtin__ as builtins
+else:
     import builtins
     def unicode(x): return str(x)
-else:
-    import __builtin__ as builtins
 
 # .. get available packages ..
 try:
@@ -903,18 +903,18 @@ def inner_wrapper(f):
 # globally defined (global variables is not enough
 # for all cases, e.g. a script that imports another
 # script where @profile is used)
-if PY3:
+if PY2:
     def exec_with_profiler(filename, profiler):
         builtins.__dict__['profile'] = profiler
-        # shadow the profile decorator defined above
         ns = dict(_CLEAN_GLOBALS, profile=profiler)
-        with open(filename) as f:
-            exec(compile(f.read(), filename, 'exec'), ns, ns)
+        execfile(filename, ns, ns)
 else:
     def exec_with_profiler(filename, profiler):
         builtins.__dict__['profile'] = profiler
+        # shadow the profile decorator defined above
         ns = dict(_CLEAN_GLOBALS, profile=profiler)
-        execfile(filename, ns, ns)
+        with open(filename) as f:
+            exec(compile(f.read(), filename, 'exec'), ns, ns)
 
 
 class LogFile(object):