diff --git a/doc/guide/myelin.md b/doc/guide/myelin.md
index 7327ec3a..667ade0c 100644
--- a/doc/guide/myelin.md
+++ b/doc/guide/myelin.md
@@ -31,7 +31,7 @@ file:
 from tensorflow.examples.tutorials.mnist import input_data
 import tensorflow as tf
 from sling.myelin import Flow
-from sling.myelin import Builder
+from sling.myelin.tf import Extractor
 
 # Import data.
 mnist = input_data.read_data_sets("/tmp/mnist", one_hot=True)
@@ -57,8 +57,8 @@ for _ in range(1000):
 
 # Save model to flow file.
 flow = Flow()
-builder = Builder(sess, flow)
-builder.add(flow.func("classifier"), [x], [y])
+extractor = Extractor(sess, flow)
+extractor.add(flow.func("classifier"), [x], [y])
 flow.save("/tmp/mnist.flow")
 ```
 
@@ -75,7 +75,7 @@ a flow file:
 ```python
 import tensorflow as tf
 from sling.myelin import Flow
-from sling.myelin import Builder
+from sling.myelin.tf import Extractor
 
 # Load Tensorflow checkpoint.
 sess = tf.Session()
@@ -84,12 +84,12 @@ saver.restore(sess, '/tmp/mnist.ckpt')
 
 # Create Myelin flow.
 flow = Flow()
-builder = Builder(sess, flow)
+extractor = Extractor(sess, flow)
 
 # Extract flow from graph.
 inputs = [sess.graph.get_tensor_by_name("x:0")]
 outputs = [sess.graph.get_tensor_by_name("y:0")]
-builder.add(flow.func("classifier"), inputs, outputs)
+extractor.add(flow.func("classifier"), inputs, outputs)
 
 # Save flow.
 flow.save("/tmp/mnist.flow")
diff --git a/python/myelin/builder.py b/python/myelin/builder.py
index 59c5c13b..5034e0e1 100644
--- a/python/myelin/builder.py
+++ b/python/myelin/builder.py
@@ -15,9 +15,6 @@
 
 """Myelin function builder and expression evaluator."""
 
-import math
-from struct import pack
-
 from flow import Variable
 from flow import Function
 from flow import Flow
diff --git a/python/myelin/flow.py b/python/myelin/flow.py
index 4e3b0a44..c00b8862 100644
--- a/python/myelin/flow.py
+++ b/python/myelin/flow.py
@@ -87,7 +87,7 @@ def __init__(self, filename):
       f.readinto(b)
     self.view = memoryview(b)
     self.next = 0  # index of next byte to read
-  
+
   def slice(self, size):
     """Returns a slice of given size from the current byte and skips ahead."""
     current = self.next
@@ -267,7 +267,7 @@ def add_attr(self, name, value):
   def get_attr(self, name):
     """Get blob attribute as a string or None."""
     return self.attrs.get(name, None)
-    
+
 class Flow:
   """Flow with variables, operations, and functions."""
 
@@ -288,7 +288,7 @@ def func(self, name):
       self.funcs[name] = f
     return f
 
-  def var(self, name, type="float32", shape=[]):
+  def var(self, name, type="float32", shape=None):
     """Add variable to flow."""
     if isinstance(name, Variable): return name
     v = self.vars.get(name, None)
@@ -296,7 +296,7 @@ def var(self, name, type="float32", shape=[]):
       v = Variable(name)
       self.vars[name] = v
       v.type = type
-      v.shape = shape
+      if shape != None: v.shape = shape
     return v
 
   def op(self, name):
@@ -526,7 +526,7 @@ def load(self, filename):
       if ref: var.ref = True
       data_size = f.read_long()
       var.data = f.slice(data_size)  # avoid creating a copy
-      
+
     num_ops = f.read_int()
     for _ in xrange(num_ops):
       name = f.read_string()
diff --git a/python/myelin/tf.py b/python/myelin/tf.py
new file mode 100644
index 00000000..b401e287
--- /dev/null
+++ b/python/myelin/tf.py
@@ -0,0 +1,120 @@
+# Copyright 2018 Google Inc. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+
+def attr_str(value):
+  """ Convert attribute to string value."""
+  if isinstance(value, bool):
+    return "true" if value else "false"
+  elif isinstance(value, int):
+    return str(value)
+  elif isinstance(value, long):
+    return str(value)
+  elif isinstance(value, str):
+    return value
+  elif isinstance(value, list):
+    l = []
+    for v in value: l.append(attr_str(v))
+    return ",".join(l)
+  elif value.__class__.__name__ == "TensorShapeProto":
+    dims = []
+    for d in value.dim: dims.append(str(d.size))
+    return "x".join(dims)
+  elif value.__class__.__name__ == "TensorProto":
+    return str(value)
+  elif value.__class__.__name__ == "DType":
+    return value.name
+  else:
+    return str(type(value)) + ":" + str(value).replace('\n', ' ')
+
+class Extractor:
+  """Extract myelin flow from tensorflow graph."""
+
+  def __init__(self, sess, flow):
+    """Initialize empty flow builder."""
+    self.sess = sess
+    self.feed = None
+    self.flow = flow
+    self.vars = []
+    self.ops = []
+
+  def add(self, func, inputs, outputs):
+    """Add ops to flow."""
+    for var in outputs:
+      self.expand(func, var, inputs)
+
+  def expand(self, func, var, inputs):
+    """Traverse graphs and add ops to flow."""
+    if var not in self.vars:
+      # Add new variable to flow.
+      self.vars.append(var)
+      v = self.flow.var(var.name, var.dtype.base_dtype.name, [])
+
+      # Get data for constants and variables.
+      if var.op.type in ["Const", "ConstV2"]:
+        v.data = tf.contrib.util.constant_value(var)
+      elif var.op.type in ["Variable", "VariableV2"]:
+        if self.feed is None:
+          v.data = var.eval(session=self.sess)
+        else:
+          v.data = self.sess.run(var, feed_dict=self.feed)
+
+      # Get shape.
+      if v.data is None:
+        shape = var.get_shape()
+        for d in shape.as_list():
+          if d != None:
+            v.shape.append(d)
+          else:
+            v.shape.append(-1)
+      else:
+        for d in v.data.shape:
+          v.shape.append(d)
+
+      if not var in inputs:
+        op = var.op
+        if op not in self.ops:
+          # Add new operation to flow function.
+          self.ops.append(op)
+          o = self.flow.op(op.name)
+          func.add(o)
+          o.type = op.type
+          for input in op.inputs:
+            o.add_input(self.flow.var(input.name))
+          for output in op.outputs:
+            o.add_output(self.flow.var(output.name))
+          for a in op.node_def.attr:
+            o.add_attr(a, attr_str(op.get_attr(a)))
+
+          # Traverse dependencies.
+          for dep in op.inputs:
+            self.expand(func, dep, inputs)
+
+
+  def compute_shapes(self):
+    """Compute shapes for variables with missing shape information."""
+    # Find all variables with missing shape information.
+    missing = {}
+    for var in self.vars:
+      v = self.flow.var(var.name)
+      if not v.shape_defined():
+        missing[v] = var
+
+    if len(missing) > 0:
+      # Compute variables from feed.
+      results = self.sess.run(missing, feed_dict=self.feed)
+
+      # Use the shape of the computed variables for the flow.
+      for v in results:
+        v.shape = results[v].shape
\ No newline at end of file
diff --git a/tools/build-wheel.py b/tools/build-wheel.py
index ddcf151d..fc83aaa2 100644
--- a/tools/build-wheel.py
+++ b/tools/build-wheel.py
@@ -66,6 +66,13 @@ def sha256_content_checksum(data):
   'python/flags.py': '$DATA$/sling/flags.py',
   'python/log.py': '$DATA$/sling/log.py',
 
+  'python/myelin/__init__.py': '$DATA$/sling/myelin/__init__.py',
+  'python/myelin/builder.py': '$DATA$/sling/myelin/builder.py',
+  'python/myelin/flow.py': '$DATA$/sling/myelin/flow.py',
+  'python/myelin/lexical_encoder.py': '$DATA$/sling/myelin/lexical_encoder.py',
+  'python/myelin/nn.py': '$DATA$/sling/myelin/nn.py',
+  'python/myelin/tf.py': '$DATA$/sling/myelin/tf.py',
+
   'python/nlp/__init__.py': '$DATA$/sling/nlp/__init__.py',
   'python/nlp/document.py': '$DATA$/sling/nlp/document.py',
   'python/nlp/parser.py': '$DATA$/sling/nlp/parser.py',