MAINT: Prefer signature over formatargspec

Prefer modern method to get signature over deprecated method

statsmodels/base/wrapper.py

@@ -96,10 +96,15 @@ def wrapper(self, *args, **kwargs):
  obj = data.wrap_output(func(results, *args, **kwargs), how)
  return obj
 
- argspec = getargspec(func)
- formatted = inspect.formatargspec(argspec[0], varargs=argspec[1],
- defaults=argspec[3])
-
+ try: # Python 3.3+
+ sig = inspect.signature(func)
+ formatted = str(sig)
+ except AttributeError:
+ # TODO: Remove when Python 2.7 is dropped
+ argspec = getargspec(func)
+ formatted = inspect.formatargspec(argspec[0],
+ varargs=argspec[1],
+ defaults=argspec[3])
  func_name = get_function_name(func)
 
  wrapper.__doc__ = "%s%s\n%s" % (func_name, formatted, wrapper.__doc__)