ECC-1790: Python3 bindings: Add codes_get_offset

Author: shahramn

CHANGELOG.rst

@@ -2,8 +2,14 @@
 Changelog for eccodes-python
 ============================
 
+1.7.1 (2024-MM-DD)
+--------------------
+
+- Add codes_get_offset
+
 1.7.0 (2024-02-26)
 --------------------
+
 - ECC-1761: Add function to extract message offsets and sizes
 - ECC-1742: Add function to clone only the meta-data of a message
 

eccodes/eccodes.py

@@ -73,6 +73,7 @@
 from gribapi import grib_get_message_offset as codes_get_message_offset
 from gribapi import grib_get_message_size as codes_get_message_size
 from gribapi import grib_get_native_type as codes_get_native_type
+from gribapi import grib_get_offset as codes_get_offset
 from gribapi import grib_get_size as codes_get_size
 from gribapi import grib_get_string as codes_get_string
 from gribapi import grib_get_string_array as codes_get_string_array
@@ -263,6 +264,7 @@
     "codes_get_message_size",
     "codes_get_message",
     "codes_get_native_type",
+    "codes_get_offset",
     "codes_get_size",
     "codes_get_string_array",
     "codes_get_string_length",

gribapi/grib_api.h

@@ -100,6 +100,7 @@ int grib_nearest_find_multiple(const grib_handle* h, int is_lsm,
     double* outlats, double* outlons,
     double* values, double* distances, int* indexes);
 
+int grib_get_offset(const grib_handle* h, const char* key, size_t* offset);
 int grib_get_size(const grib_handle* h, const char* key,size_t *size);
 
 int grib_get_length(const grib_handle* h, const char* key,size_t *length);

gribapi/gribapi.py

@@ -578,10 +578,27 @@ def grib_multi_append(ingribid, startsection, multigribid):
     GRIB_CHECK(lib.grib_multi_handle_append(h, startsection, mh))
 
 
+@require(msgid=int, key=str)
+def grib_get_offset(msgid, key):
+    """
+    @brief Get the byte offset of a key. If several keys of the same name
+    are present, the offset of the last one is returned
+
+    @param msgid      id of the message loaded in memory
+    @param key        name of the key
+    @exception CodesInternalError
+    """
+    h = get_handle(msgid)
+    offset_p = ffi.new("size_t*")
+    err = lib.grib_get_offset(h, key.encode(ENC), offset_p)
+    GRIB_CHECK(err)
+    return offset_p[0]
+
+
 @require(msgid=int, key=str)
 def grib_get_size(msgid, key):
     """
-    @brief Get the size of an array key.
+    @brief Get the size of a key. Return 1 for scalar keys and >1 for array keys
 
     \b Examples: \ref grib_get_keys.py "grib_get_keys.py",\ref count_messages.py "count_messages.py"
 

tests/test_eccodes.py

@@ -358,6 +358,14 @@ def test_grib_get_message_offset():
     assert eccodes.codes_get_message_offset(gid) == 0
 
 
+def test_grib_get_key_offset():
+    gid = eccodes.codes_grib_new_from_samples("GRIB2")
+    assert eccodes.codes_get_offset(gid, "identifier") == 0
+    assert eccodes.codes_get_offset(gid, "discipline") == 6
+    assert eccodes.codes_get_offset(gid, "offsetSection1") == 16
+    assert eccodes.codes_get_offset(gid, "7777") == 175
+
+
 def test_grib_clone():
     gid = eccodes.codes_grib_new_from_samples("GRIB2")
     clone = eccodes.codes_clone(gid)