atpalmer-python
diff --git a/‎README.md
Lines changed: 13 additions & 0 deletions b/‎README.md
Lines changed: 13 additions & 0 deletions
diff --git a/‎src/cstring.c
Lines changed: 26 additions & 2 deletions b/‎src/cstring.c
Lines changed: 26 additions & 2 deletions
diff --git a/‎test/test_methods.py
Lines changed: 17 additions & 0 deletions b/‎test/test_methods.py
Lines changed: 17 additions & 0 deletions
@@ -10,6 +10,7 @@ Alternate string representation to the built-in `str` type.
 
 ## Methods
 
+
 ### count(substring [,start [,end]])
 
 See: https://docs.python.org/3/library/stdtypes.html#str.count
@@ -19,6 +20,7 @@ Notes:
 * `substring` may be a `cstring` or Python `str` object.
 * `start` and `end`, if provided, are _byte_ indexes.
 
+
 ### find(substring [,start [,end]])
 
 See: https://docs.python.org/3/library/stdtypes.html#str.find
@@ -28,6 +30,17 @@ Notes:
 * `substring` may be a `cstring` or Python `str` object.
 * `start` and `end`, if provided, are _byte_ indexes.
 
+
+### index(substring [,start [,end]])
+
+See: https://docs.python.org/3/library/stdtypes.html#str.index
+
+Notes:
+
+* `substring` may be a `cstring` or Python `str` object.
+* `start` and `end`, if provided, are _byte_ indexes.
+
+
 ## TODO
 
 * Write docs (see `str` type docs)
 
@@ -262,11 +262,34 @@ PyObject *cstring_find(PyObject *self, PyObject *args) {
 
     char *p = strstr(params.start, params.substr);
     if(!p)
-        return PyLong_FromLong(-1);
+        goto err;
     if(p + params.substr_len > params.end)
-        return PyLong_FromLong(-1);
+        goto err;
 
     return PyLong_FromSsize_t(p - CSTRING_VALUE(self));
+
+err:
+    return PyLong_FromLong(-1);
+}
+
+PyDoc_STRVAR(index__doc__, "");
+PyObject *cstring_index(PyObject *self, PyObject *args) {
+    struct _substr_params params;
+
+    if(!_parse_substr_args(self, args, &params))
+        return NULL;
+
+    char *p = strstr(params.start, params.substr);
+    if(!p)
+        goto err;
+    if(p + params.substr_len > params.end)
+        goto err;
+
+    return PyLong_FromSsize_t(p - CSTRING_VALUE(self));
+
+err:
+    PyErr_SetString(PyExc_ValueError, "substring not found");
+    return NULL;
 }
 
 static PySequenceMethods cstring_as_sequence = {
@@ -285,6 +308,7 @@ static PyMappingMethods cstring_as_mapping = {
 static PyMethodDef cstring_methods[] = {
     {"count", cstring_count, METH_VARARGS, count__doc__},
     {"find", cstring_find, METH_VARARGS, find__doc__},
+    {"index", cstring_index, METH_VARARGS, index__doc__},
     {0},
 };
 
 
@@ -1,3 +1,4 @@
+import pytest
 from cstring import cstring
 
 
@@ -35,3 +36,19 @@ def test_find_missing():
     target = cstring('hello')
     assert target.find('lo', 0, 4) == -1
 
+
+def test_index():
+    target = cstring('hello')
+    assert target.index('lo') == 3
+
+
+def test_index_with_start():
+    target = cstring('hello')
+    assert target.index('lo', 3) == 3
+
+
+def test_index_missing():
+    target = cstring('hello')
+    with pytest.raises(ValueError):
+        return target.index('lo', 0, 4)
+