str.expandtabs

src/runtime/str.cpp

@@ -2142,6 +2142,82 @@ extern "C" void PyString_ConcatAndDel(register PyObject** pv, register PyObject*
     PyString_Concat(pv, w);
 }
 
+static PyObject* string_expandtabs(PyStringObject* self, PyObject* args) noexcept {
+    const char* e, *p, *qe;
+    char* q;
+    Py_ssize_t i, j, incr;
+    PyObject* u;
+    int tabsize = 8;
+
+    if (!PyArg_ParseTuple(args, "|i:expandtabs", &tabsize))
+        return NULL;
+
+    /* First pass: determine size of output string */
+    i = 0; /* chars up to and including most recent \n or \r */
+    j = 0; /* chars since most recent \n or \r (use in tab calculations) */
+    e = PyString_AS_STRING(self) + PyString_GET_SIZE(self); /* end of input */
+    for (p = PyString_AS_STRING(self); p < e; p++) {
+        if (*p == '\t') {
+            if (tabsize > 0) {
+                incr = tabsize - (j % tabsize);
+                if (j > PY_SSIZE_T_MAX - incr)
+                    goto overflow1;
+                j += incr;
+            }
+        } else {
+            if (j > PY_SSIZE_T_MAX - 1)
+                goto overflow1;
+            j++;
+            if (*p == '\n' || *p == '\r') {
+                if (i > PY_SSIZE_T_MAX - j)
+                    goto overflow1;
+                i += j;
+                j = 0;
+            }
+        }
+    }
+
+    if (i > PY_SSIZE_T_MAX - j)
+        goto overflow1;
+
+    /* Second pass: create output string and fill it */
+    u = PyString_FromStringAndSize(NULL, i + j);
+    if (!u)
+        return NULL;
+
+    j = 0;                                             /* same as in first pass */
+    q = PyString_AS_STRING(u);                         /* next output char */
+    qe = PyString_AS_STRING(u) + PyString_GET_SIZE(u); /* end of output */
+
+    for (p = PyString_AS_STRING(self); p < e; p++) {
+        if (*p == '\t') {
+            if (tabsize > 0) {
+                i = tabsize - (j % tabsize);
+                j += i;
+                while (i--) {
+                    if (q >= qe)
+                        goto overflow2;
+                    *q++ = ' ';
+                }
+            }
+        } else {
+            if (q >= qe)
+                goto overflow2;
+            *q++ = *p;
+            j++;
+            if (*p == '\n' || *p == '\r')
+                j = 0;
+        }
+    }
+
+    return u;
+
+overflow2:
+    Py_DECREF(u);
+overflow1:
+    PyErr_SetString(PyExc_OverflowError, "new string is too long");
+    return NULL;
+}
 
 static Py_ssize_t string_buffer_getreadbuf(PyObject* self, Py_ssize_t index, const void** ptr) noexcept {
     RELEASE_ASSERT(index == 0, "");
@@ -2194,6 +2270,7 @@ static PyMethodDef string_methods[] = {
     { "rsplit", (PyCFunction)string_rsplit, METH_VARARGS, NULL },
     { "find", (PyCFunction)string_find, METH_VARARGS, NULL },
     { "rfind", (PyCFunction)string_rfind, METH_VARARGS, NULL },
+    { "expandtabs", (PyCFunction)string_expandtabs, METH_VARARGS, NULL },
 };
 
 void setupStr() {

test/tests/str_functions.py

@@ -136,3 +136,6 @@ try:
     print "hello world".index("goodbye")
 except:
     print "threw exception"
+
+print repr("hello\tworld\t".expandtabs())
+print repr("hello\tworld\t".expandtabs(12))