diff --git a/tests/test_base.py b/tests/test_base.py
index c67dd6e..474b9fa 100644
--- a/tests/test_base.py
+++ b/tests/test_base.py
@@ -1,7 +1,5 @@
 # -*- coding: utf-8 -*-
 
-import linecache
-
 import pytest
 
 import thriftpy
@@ -70,8 +68,3 @@ def test_parse_spec():
 
     for spec, res in cases:
         assert parse_spec(*spec) == res
-
-
-def test_init_func():
-    thriftpy.load("addressbook.thrift")
-    assert linecache.getline('<generated PhoneNumber.__init__>', 1) != ''
diff --git a/tests/test_type.py b/tests/test_type.py
index b4e27ff..8df4559 100644
--- a/tests/test_type.py
+++ b/tests/test_type.py
@@ -1,10 +1,61 @@
 # -*- coding: utf-8 -*-
 
 from thriftpy import load
-from thriftpy.thrift import TType
+from thriftpy.thrift import TType, TPayload
 
 
 def test_set():
     s = load("type.thrift")
 
     assert s.Set.thrift_spec == {1: (TType.SET, "a_set", TType.STRING, True)}
+
+
+class Struct(TPayload):
+    thrift_spec = {
+        1: (TType.MAP, 'tdict', (TType.I32, TType.I32), False),
+        2: (TType.SET, 'tset', TType.I32, False),
+        3: (TType.LIST, 'tlist', TType.I32, False),
+    }
+
+    default_spec = [
+        ('tdict', {}),
+        ('tset', set()),
+        ('tlist', []),
+    ]
+
+
+# making an object with default values and then mutating the object should not
+# change the default values
+
+def test_mutable_default_dict():
+    s1 = Struct()
+    s1.tdict[1] = 2
+
+    s2 = Struct()
+    assert s2.tdict == {}
+
+
+def test_mutable_default_list():
+    s1 = Struct()
+    s1.tlist.append(1)
+
+    s2 = Struct()
+    assert s2.tlist == []
+
+
+def test_mutable_default_set():
+    s1 = Struct()
+    s1.tset.add(1)
+
+    s2 = Struct()
+    assert s2.tset == set()
+
+
+def test_positional_args():
+    # thriftpy instantiates TPayload objects using positional args.
+    # thriftpy.thrift.TException being the most notable example.
+    # make sure that we don't break backwards compatiblity
+    s1 = Struct({1: 2}, set([3, 4]), [5, 6])
+    assert s1.tdict == {1: 2}
+    assert s1.tset == set([3, 4])
+    assert s1.tlist == [5, 6]
diff --git a/thriftpy/thrift.py b/thriftpy/thrift.py
index bf1db20..81efc2d 100644
--- a/thriftpy/thrift.py
+++ b/thriftpy/thrift.py
@@ -9,10 +9,8 @@
 
 from __future__ import absolute_import
 
+import copy
 import functools
-import linecache
-import types
-
 from ._compat import with_metaclass
 
 
@@ -54,25 +52,28 @@ def __init__(self, name='Alice', number=None):
             self.number = number
     """
     if not spec:
-        def __init__(self):
-            pass
-        return __init__
-
-    varnames, defaults = zip(*spec)
-
-    args = ', '.join(map('{0[0]}={0[1]!r}'.format, spec))
-    init = "def __init__(self, {0}):\n".format(args)
-    init += "\n".join(map('    self.{0} = {0}'.format, varnames))
-
-    name = '<generated {0}.__init__>'.format(cls.__name__)
-    code = compile(init, name, 'exec')
-    func = next(c for c in code.co_consts if isinstance(c, types.CodeType))
-
-    # Add a fake linecache entry so debuggers and the traceback module can
-    # better understand our generated code.
-    linecache.cache[name] = (len(init), None, init.splitlines(True), name)
-
-    return types.FunctionType(func, {}, argdefs=defaults)
+        spec = []
+
+    def __init__(self, *args, **kwargs):
+        # __init__ might get passed args or kwargs assume that positional args
+        # are in the same order specified by spec anything else is a kwarg
+        i = len(args)
+        arg_spec = spec[:i]
+        kw_spec = spec[i:]
+
+        for arg, (name, _) in zip(args, arg_spec):
+            setattr(self, name, arg)
+
+        for name, default in kw_spec:
+            if name in kwargs:
+                setattr(self, name, kwargs.pop(name))
+            else:
+                # make a copy of the default values so that we can mutate them
+                # without affecting anything else
+                setattr(self, name, copy.copy(default))
+        assert not kwargs
+
+    return __init__
 
 
 class TType(object):