Python 3.10/3.11: bonds package fails to import — multi-line f-string needs 3.12 (declared support is >=3.10)

[DMZ22]

financepy/products/bonds/bond.py line 1238 contains an f-string whose replacement field spans two lines:

print(f"Warning: YTM calculation did not converge for price {
        dirty_price}")

Multi-line expressions inside f-strings are a PEP 701 feature, available only on Python 3.12+. On Python 3.10 and 3.11 this is a SyntaxError at import time:

File ".../financepy/products/bonds/bond.py", line 1238
SyntaxError: unterminated string literal (detected at line 1238)

and it takes down the whole financepy.products.bonds package (its __init__.py imports bond), plus everything that imports bonds transitively — on 3.11, 17 unit-test modules fail collection for this reason (that's how I ran into it while testing #247).

Why it slips through:

• pyproject.toml declares requires-python = ">=3.10,<3.14", so pip installs happily on 3.10/3.11 where the import then fails.
• run-unit-tests.yml pins a single PYTHON_VERSION: '3.13.9', so CI never exercises the older interpreters. The line came in with e38db05 (Nov 2025).

Fix options:

1. Put the replacement field on one line (one-line change) — keeps 3.10/3.11 support; or
2. Declare reality and bump requires-python to >=3.12.

If you'd like option 1, happy to send the trivial PR; adding the minimum supported version to the CI matrix would keep this from regressing either way.

[sanjey99]

hi, i'd like to work on this. going with fix option 1 (keep the replacement field on one line, so 3.10/3.11 stays supported). also found a second instance of the same bug at line ~1548 (OAS warning) that wasn't in the original report, fixing that too. will send a pr shortly.

[DMZ22]

Great, it's all yours @sanjey99 — and your second find is real. Confirming the exact locations, since a partial fix here is easy to ship by accident: compile() stops at the first SyntaxError in a file, so the second one stays invisible until the first is patched.

I scanned every .py in the package for f-strings whose replacement field spans a newline (the PEP 701 construct that needs ≥3.12). There are exactly two, both in financepy/products/bonds/bond.py:

• 1238 — print(f"Warning: YTM calculation did not converge for price { → dirty_price}")
• 1549 — print(f"Warning: OAS calculation did not converge for price { → dirty_price}")

Nothing else in the package trips a 3.11 parse, so joining those two onto one line each is the complete fix.

Worth flagging separately, because it explains why this reached a release at all — the CI cannot catch it:

• pyproject.toml declares requires-python = ">=3.10,<3.14", i.e. 3.10 / 3.11 / 3.12 / 3.13.
• run-unit-tests.yml and run-golden-tests.yml both pin PYTHON_VERSION: '3.13.9' — the only declared-supported version where this syntax is legal.
• pylint.yml runs on 3.8, which is below the declared floor.
• docs.yml is the only job on 3.11, and it would have caught this. But it triggers on push: branches: [main], and the repository's only branch is master — so it has never executed. gh run list --workflow=docs.yml returns nothing at all.

So a python-version matrix of at least ["3.10", "3.13"] on the unit-test workflow would stop this class of regression permanently, and repointing docs.yml at master would fix a workflow that is currently dead. Both are separate from your fix — happy to send either as its own PR if the maintainer wants, but I don't want to get in the way of yours.