hp wing

[juliet3570]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior. e.g. A python script.

Logs
If applicable, add logs to help explain your problem.

Expected behavior
A clear and concise description of what you expected to happen.

Environment and software version (please complete the following information):

• OS: [e.g. Ubuntu 20.04.3 LTS, Mac OS 12.1]
• PyCardano Version [e.g. 0.1.1]

Additional context
Add any other context about the problem here.

[juliet3570]

The TransactionBuilder fails to estimate fees correctly when including a PlutusData datum that contains mental health screening results (large metadata strings). This results in an InsufficientFunds error during transaction submission, even when the wallet has a sufficient balance for the estimated fee.

To Reproduce
Steps to reproduce the behavior:

Initialize a BlockFrostChainContext.

Create a TransactionBuilder.

Add an output with a complex PlutusData object (representing the mental health wellness score and family support flags).

Call builder.build_and_sign().

Observe that the transaction is rejected by the node due to a fee mismatch or insufficient collateral.

Example Script:

Python

from pycardano import TransactionBuilder, BlockFrostChainContext, Network

Initialize context

context = BlockFrostChainContext("your_project_id", Network.TESTNET)

Build transaction with mental health datum

builder = TransactionBuilder(context)
builder.add_input(user_utxo)
builder.add_output(TransactionOutput(address, amount, datum=mental_health_datum))

This call fails or produces an incorrect fee estimate

signed_tx = builder.build_and_sign([payment_signing_key])
Logs
Plaintext

pycardano.exception.TransactionFailedException:
"Submit failed: Expected fee: 185205 Lovelace, but received: 172401 Lovelace.
The datum size increased the execution units beyond the initial estimate."
Expected behavior
The TransactionBuilder should accurately calculate the script data hash and execution units for the provided datum size so that the estimated fee matches the actual requirements of the Cardano network.

Environment and software version
OS: Ubuntu 22.04 LTS

PyCardano Version: 0.9.2 (or the latest 2026 stable release)

Python Version: 3.11

Additional context
This bug is specifically affecting the MediBora mental health module because we are passing larger-than-average strings (screening answers from boys and girls) into the datum. Smaller data packets do not seem to trigger the same estimation error.

[cffls]

It seems not possible to debug this without the actual datum. Could you please provide a reproducible example?

[juliet3570]

ok

…

On Sat, Feb 28, 2026 at 7:56 PM Jerry ***@***.***> wrote: *cffls* left a comment (Python-Cardano/pycardano#483) <#483 (comment)> It seems not possible to debug this without the actual datum. Could you please provide a reproducible example? — Reply to this email directly, view it on GitHub <#483 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BWKJV7HFLTVWFG3T5ZMIUFD4OHCDVAVCNFSM6AAAAACWCTIRTKVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTSNZXGQYTSNZQGM> . You are receiving this because you authored the thread.Message ID: ***@***.***>