Extending pre-existing RNTuple

[Superharz]

Question

Is there an existing extending mechanism for already existing RNTuples in root files?

Versions

• Python: 3.13.12
• Uproot: 5.7.1
• Awkward: 2.8.12
• Numpy: 2.4.2

File Creation

I have created a RNTuple in a file as described in the docs:

with uproot.recreate("example.root") as file:
    data = {"my_int": [1,2], "my_vector": [[1,2], [3,4,5]]}
    rntuple = file.mkrntuple("my_rntuple", data)

RNTuple extending

Now I would like to later reopen this file and extend the RNTuple:

with uproot.open("example.root:my_rntuple") as rntuple:
    data = {"my_int": [1,2], "my_vector": [[1,2], [3,4,5]]}
    rntuple.extend(data)

This results in

AttributeError: 'Model_ROOT_3a3a_RNTuple' object has no attribute 'extend'

I also tried to use uproot.update:

with uproot.update("example.root") as file:
    data = {"my_int": [1,2], "my_vector": [[1,2], [3,4,5]]}
    rntuple = file["my_rntuple"]
    rntuple.extend(data)

This results in

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[61], line 3
      1 with uproot.update("example.root") as file:
      2     data = {"my_int": [1,2], "my_vector": [[1,2], [3,4,5]]}
----> 3     rntuple = file["my_rntuple"]
      4     rntuple.extend(data)

File [\Lib\site-packages\uproot\writing\writable.py:983](Lib/site-packages/uproot/writing/writable.py#line=982), in WritableDirectory.__getitem__(self, where)
    981 if self._file.sink.closed:
    982     raise ValueError("cannot get data from a closed file")
--> 983 return self._get_del_search(where, True)

File [\Lib\site-packages\uproot\writing\writable.py:976](Lib/site-packages/uproot/writing/writable.py#line=975), in WritableDirectory._get_del_search(self, where, isget)
    973     item, cycle = where, None
    975 if isget:
--> 976     return self._get(item, cycle)
    977 else:
    978     return self._del(item, cycle)

File [\Lib\site-packages\uproot\writing\writable.py:1020](Lib/site-packages/uproot/writing/writable.py#line=1019), in WritableDirectory._get(self, name, cycle)
   1018         return self._file._get_ntuple(key.seek_location)
   1019     else:
-> 1020         raise TypeError(
   1021             "WritableDirectory cannot view preexisting RNTuple; open the file with uproot.open instead of uproot.recreate or uproot.update"
   1022         )
   1024 else:
   1026     def get_chunk(start, stop):

TypeError: WritableDirectory cannot view preexisting RNTuple; open the file with uproot.open instead of uproot.recreate or uproot.update

[ariostas]

Hi @Superharz, thanks for bringing this up! As far as I know there is also no way to do this for TTree. But this is something we should definitely support for RNTuples since it will be a lot more straightforward to implement! I'll add this to the roadmap for 2026.