diff --git a/fmt/fmt.py b/fmt/fmt.py
index ce33f5e..019eab3 100644
--- a/fmt/fmt.py
+++ b/fmt/fmt.py
@@ -9,10 +9,18 @@
 from functools import partial
 
 
+PY3 = sys.version_info[0] == 3
+if PY3:
+    fmt_types = str, bytes
+else:
+    fmt_types = basestring, unicode  # noqa: F821
+
+
 class Fmt(object):
 
     def __init__(self):
         self._g_ns = {}
+        self._nodes_cache = {}
 
     def register(self, name, value, update=False):
         if not update and name in self._g_ns:
@@ -24,13 +32,21 @@ def mregister(self, ns, update=False):
             self.register(k, v, update)
 
     def __call__(self, f_str, *_args):
+        if not isinstance(f_str, fmt_types):
+            raise ValueError('Unsupported type as format '
+                             'string: {}({})'.format(type(f_str), f_str))
         frame = sys._getframe(1)
         # locals will cover globals
         ns = deepcopy(self._g_ns)
         ns.update(frame.f_globals)
         ns.update(frame.f_locals)
 
-        nodes = Parser(f_str).parse()
+        # cache nodes, if already parsed
+        nodes = self._nodes_cache.get(f_str, None)
+        if nodes is None:
+            nodes = Parser(f_str).parse()
+            self._nodes_cache[f_str] = nodes
+
         try:
             return generate(nodes, ns)
         finally:
@@ -45,6 +61,18 @@ def generate(nodes, namespace):
 
 
 class Node(object):
+    # flyweight pattern: cache instances
+    _instances = {}
+
+    def __new__(cls, *args, **kwargs):
+        key = (cls, args, tuple(kwargs.items()))
+        instance = cls._instances.get(key, None)
+        if instance is None:
+            instance = super(Node, cls).__new__(cls)
+            instance.__init__(*args, **kwargs)
+            cls._instances[key] = instance
+        return instance
+
     def generate(self, ns):
         raise NotImplementedError()
 
diff --git a/tests/test_fmt.py b/tests/test_fmt.py
index 5d49ee9..19033b8 100644
--- a/tests/test_fmt.py
+++ b/tests/test_fmt.py
@@ -1,8 +1,35 @@
 # -*- coding: utf-8 -*-
 
 import sys
-from datetime import datetime
-import fmt as  f
+from datetime import datetime  # noqa
+from fmt.fmt import Fmt, Parser, Text
+import fmt as f
+
+
+def test_parsed_nodes_been_cached(monkeypatch):
+    call_count = []
+
+    def _parse(self):
+        call_count.append(1)
+        return [Text('baz')]
+
+    monkeypatch.setattr(Parser, 'parse', _parse)
+    fmt = Fmt()
+
+    count = 0
+    for f_str in ('foo', 'bar'):
+        count += 1
+        fmt(f_str)
+        assert f_str in fmt._nodes_cache
+        assert len(call_count) == count
+
+        value = fmt._nodes_cache[f_str][0]
+
+        for _ in range(5):
+            fmt(f_str)
+            assert f_str in fmt._nodes_cache
+            assert len(call_count) == count, f_str
+            assert id(value) == id(fmt._nodes_cache[f_str][0])
 
 
 g_foo = 'global-foo'
@@ -34,6 +61,7 @@ def test_namespace():
 def test_closure_namespace():
     def outer(x):
         y = 'yy'
+
         def inner():
             z = 'zz'
             globals_, locals_ = get_namesapce(x, y)
@@ -54,7 +82,9 @@ def test_fmt():
     l_bar = 'local-bar'
     ls_num = range(5)
     ls_ch = ['a', 'b', 'c', 'd', 'e']
+
     class Baz(object):
+
         def __str__(self):
             return 'BAZ'
 
@@ -77,19 +107,21 @@ def __str__(self):
     assert '1314' == f('{func(x, y)}')
 
     def outer(arg):
+
         def inner():
             assert '{ outer-arg }' == f('{{ {arg} }}', arg)
         return inner
+
     outer('outer-arg')()
 
-    assert '[0, 1, 2, 3, 4]' == f('{list(range(5))}')  # Py3 range return iterator
+    # Py3 range return iterator
+    assert '[0, 1, 2, 3, 4]' == f('{list(range(5))}')
     assert '[0, 1, 2, 3, 4]' == f('{[i for i in ls_num]}')
     if sys.version_info[0] == 2:
         assert 'set([0, 1, 2, 3, 4])' == f('{{i for i in ls_num}}')
     else:
         assert '{0, 1, 2, 3, 4}' == f('{{i for i in ls_num}}')
 
-
     assert ("{0: 'a', 1: 'b', 2: 'c', 3: 'd', 4: 'e'}" ==
             f('{{k:v for k,v in zip(ls_num, ls_ch)}}'))
     assert '[1, 2, 3, 4, 5]' == f('{list(map(lambda x: x+1, ls_num))}')
diff --git a/tests/test_node.py b/tests/test_node.py
index a590084..8abe23f 100644
--- a/tests/test_node.py
+++ b/tests/test_node.py
@@ -4,6 +4,20 @@
 from fmt.fmt import Text, Constant, Expression
 
 
+def test_flyweight():
+    assert id(Text('foo', 'bar')) == id(Text('foo', 'bar'))
+    assert id(Constant('foo', 'bar')) == id(Constant('foo', 'bar'))
+    assert id(Expression('foo', 'bar')) == id(Expression('foo', 'bar'))
+
+    assert id(Text('foo', 'bar')) != id(Text('bar', 'foo'))
+    assert id(Constant('foo', 'bar')) != id(Constant('bar', 'foo'))
+    assert id(Expression('foo', 'bar')) != id(Expression('bar', 'foo'))
+
+    assert id(Text('foo', 'bar')) != id(Constant('foo', 'bar'))
+    assert id(Text('foo', 'bar')) != id(Expression('foo', 'bar'))
+    assert id(Constant('foo', 'bar')) != id(Expression('foo', 'bar'))
+
+
 def test_Text():
     text = 'I am a good man, /(ㄒoㄒ)/~~'
     assert text == Text(text).generate(None)