ImportError: cannot import name 'trapz' from 'scipy.integrate'

TL;DR: scipy 1.14 removed the old trapz name; it is now called trapezoid. Change your import to from scipy.integrate import trapezoid (alias it as trapz if you like) or pin scipy below 1.14.

The error

ImportError: cannot import name 'trapz' from 'scipy.integrate'

Fix it

1. Update the import (keeps working on old scipy too if you alias):

   from scipy.integrate import trapezoid as trapz

   Expected: existing trapz(...) call sites keep working.

2. Or use the new name directly:

   from scipy.integrate import trapezoid

3. Verify:

   python -c "from scipy.integrate import trapezoid; print(trapez([1,2,3]))"

   Expected: prints 4.0.

4. Stopgap if you cannot edit the code: pip install "scipy<1.14". Expected: old import works again.

When this applies

Use this when code written for older scipy does from scipy.integrate import trapz on scipy 1.14+.

When it does not apply

If the error names cumtrapz, its new name is cumulative_trapezoid. If scipy itself fails to import, reinstall scipy.

Compatibility

scipy 1.14+. trapezoid exists since scipy 1.6, so the aliased import works on scipy 1.6 through 2.x.

Root cause

scipy renamed trapz to trapezoid for a clearer API and kept trapz as a deprecated alias for years before removing it in 1.14. Code that never migrated breaks at import.

Edge cases

The sibling cumtrapz was renamed cumulative_trapezoid in the same cleanup; check for it in the same files. Libraries should use the try/except import pattern to support both eras.

GitHub issue fermipy/fermipy#665 reports ImportError: cannot import name 'trapz' from 'scipy.integrate' after upgrading scipy. The verified fix: scipy 1.14 removed the long-deprecated trapz alias in favor of trapezoid, so the import becomes from scipy.integrate import trapezoid (or import trapezoid as trapz to keep old call sites working); pinning scipy below 1.14 also works as a stopgap. Full thread: https://github.com/fermipy/fermipy/issues/665