diff --git a/Cargo.lock b/Cargo.lock
index f174719..562485c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -29,6 +29,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "anyhow"
+version = "1.0.86"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b3d1d046238990b9cf5bcde22a3fb3584ee5cf65fb2765f454ed428c7a0063da"
+
 [[package]]
 name = "approx"
 version = "0.5.1"
@@ -562,6 +568,7 @@ dependencies = [
 name = "oxli"
 version = "0.1.0"
 dependencies = [
+ "anyhow",
  "pyo3",
  "sourmash",
 ]
@@ -681,6 +688,7 @@ version = "0.19.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e681a6cfdc4adcc93b4d3cf993749a4552018ee0a9b65fc0ccfad74352c72a38"
 dependencies = [
+ "anyhow",
  "cfg-if",
  "indoc",
  "libc",
diff --git a/Cargo.toml b/Cargo.toml
index a9bbc7c..159a6db 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,5 +9,6 @@ name = "oxli"
 crate-type = ["cdylib"]
 
 [dependencies]
-pyo3 = "0.19.0"
+pyo3 = { version="0.19.0", features = ["extension-module", "anyhow"] }
 sourmash = "0.15.1"
+anyhow = "1.0.86"
diff --git a/src/lib.rs b/src/lib.rs
index ea30045..c5ef467 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,60 +1,107 @@
 use pyo3::prelude::*;
+use pyo3::exceptions::PyValueError;
+// use rayon::prelude::*;
 
+use anyhow::{Result, Error, anyhow};
 use std::collections::HashMap;
 
-use sourmash::sketch::nodegraph::Nodegraph;
+// use sourmash::sketch::nodegraph::Nodegraph;
 use sourmash::_hash_murmur;
+use sourmash::signature::SeqToHashes;
+use sourmash::encodings::HashFunctions;
+
 
 #[pyclass]
 struct KmerCountTable {
-    counts: HashMap<u64, usize>,
+    counts: HashMap<u64, u64>,
+    pub ksize: u8,
 }
 
 #[pymethods]
 impl KmerCountTable {
     #[new]
-    pub fn new() -> Self {
-        Self { counts: HashMap::new() }
+    pub fn new(ksize: u8) -> Self {
+        Self { counts: HashMap::new(), ksize }
     }
 
-    pub fn count(&mut self, kmer: String) -> PyResult<usize> {
-        let hashval = _hash_murmur(kmer.as_bytes(), 42);
+    fn hash_kmer(&self, kmer: String) -> Result<u64> {
+        if kmer.len() as u8 != self.ksize {
+            Err(anyhow!("wrong ksize"))
+        } else {
+            // mut?
+            let mut hashes = SeqToHashes::new(kmer.as_bytes(),
+                                          self.ksize.into(),
+                                          false,
+                                          false,
+                                          HashFunctions::Murmur64Dna,
+                                          42);
+
+            let mut hashval = hashes.next().unwrap();
+            Ok(hashval?)
+        }
+    }
 
-        let mut count: usize = 1;
+
+    pub fn count_hash(&mut self, hashval: u64) -> u64 {
+        let mut count: u64 = 1;
         if self.counts.contains_key(&hashval) {
             count = *self.counts.get(&hashval).unwrap();
             count = count + 1;
         }
         self.counts.insert(hashval, count);
 
-        Ok(count)
+        count
     }
 
-    pub fn get(&self, kmer: String) -> PyResult<usize> {
-        let hashval = _hash_murmur(kmer.as_bytes(), 42);
+    pub fn count(&mut self, kmer: String) -> PyResult<u64> {
+        if kmer.len() as u8 != self.ksize {
+            Err(PyValueError::new_err("kmer size does not match count table ksize"))
+        } else {
+            let hashval = _hash_murmur(kmer.as_bytes(), 42);
+            let count = self.count_hash(hashval);
+            Ok(count)
+        }
+    }
 
-        let count = match self.counts.get(&hashval) {
-            Some(count) => count,
-            None => &(0 as usize)
-        };
-        Ok(*count)
+    pub fn get(&self, kmer: String) -> PyResult<u64> {
+        if kmer.len() as u8 != self.ksize {
+            Err(PyValueError::new_err("kmer size does not match count table ksize"))
+        } else {
+            let hashval = self.hash_kmer(kmer).unwrap();
+
+            let count = match self.counts.get(&hashval) {
+                Some(count) => count,
+                None => &0
+            };
+            Ok(*count)
+        }
     }
-}
 
-/// Formats the sum of two numbers as string.
-#[pyfunction]
-fn sum_as_string(a: String) -> PyResult<usize> {
-    let mut ng: Nodegraph = Nodegraph::with_tables(23, 6, 3);
+    // Consume this DNA strnig. Return number of k-mers consumed.
+    pub fn consume(&mut self, seq: String) -> PyResult<u64> {
+        let hashes = SeqToHashes::new(seq.as_bytes(),
+                                      self.ksize.into(),
+                                      false,
+                                      false,
+                                      HashFunctions::Murmur64Dna,
+                                      42);
 
-    let hashval = _hash_murmur(a.as_bytes(), 42);
-    ng.count(hashval);
-    Ok(ng.get(hashval))
+        let mut n = 0;
+        for hash_value in hashes {
+            match hash_value {
+                Ok(0) => continue,
+                Ok(x) => { self.count_hash(x); () }
+                Err(err) => (),
+            }
+            n += 1;
+        }
+
+        Ok(n)
+    }
 }
 
-/// A Python module implemented in Rust.
 #[pymodule]
 fn oxli(_py: Python, m: &PyModule) -> PyResult<()> {
-    m.add_function(wrap_pyfunction!(sum_as_string, m)?)?;
     m.add_class::<KmerCountTable>()?;
     Ok(())
 }
diff --git a/src/python/tests/test_basic.py b/src/python/tests/test_basic.py
index dc246dc..7c33f5b 100644
--- a/src/python/tests/test_basic.py
+++ b/src/python/tests/test_basic.py
@@ -1,9 +1,39 @@
+import pytest
 import oxli
 
 def test_simple():
-    cg = oxli.KmerCountTable()
+    cg = oxli.KmerCountTable(4)
     kmer = "ATCG"
 
     assert cg.get(kmer) == 0
     assert cg.count(kmer) == 1
     assert cg.get(kmer) == 1
+
+
+def test_wrong_ksize():
+    cg = oxli.KmerCountTable(3)
+    kmer = "ATCG"
+
+    with pytest.raises(ValueError):
+        cg.count(kmer)
+
+    with pytest.raises(ValueError):
+        cg.get(kmer)
+
+
+def test_consume():
+    cg = oxli.KmerCountTable(4)
+    kmer = "ATCG"
+
+    assert cg.consume(kmer) == 1
+    assert cg.get("ATCG") == 1
+
+
+def test_consume_2():
+    cg = oxli.KmerCountTable(4)
+    seq = "ATCGG"
+
+    assert cg.consume(seq) == 2
+    assert cg.get("ATCG") == 1
+    assert cg.get("TCGG") == 1
+    assert cg.get("CCGA") == 1 # reverse complement!