ImportError: cannot import name 'triu' from 'scipy.linalg.special_matrices'

TL;DR: scipy moved triu out of scipy.linalg.special_matrices into scipy.linalg. Change your import to from scipy.linalg import triu and it works on old and new scipy.

The error

ImportError: cannot import name 'triu' from 'scipy.linalg.special_matrices'

Fix it

1. Replace the import in your code:

   from scipy.linalg import triu

   Expected: no other changes needed; triu takes the same arguments.

2. If you maintain a library, make the import version-proof:

   try:
       from scipy.linalg import triu
   except ImportError:
       from scipy.linalg.special_matrices import triu

3. Verify:

   python -c "from scipy.linalg import triu; print(triu([[1,2],[3,4]]))"

   Expected: prints the upper-triangular matrix.

When this applies

Use this when old code or a dependency does from scipy.linalg.special_matrices import triu (or tril) on a recent scipy.

When it does not apply

If the error names a different function, look up its new location instead of guessing. If scipy itself will not import, the install is broken.

Compatibility

scipy 1.8+ (special_matrices no longer exports triu/tril). from scipy.linalg import triu works on scipy 1.x and 2.x alike.

Root cause

scipy consolidated the triangular-matrix helpers into the main linalg namespace and stopped re-exporting them from the special_matrices submodule. Code written against the old path breaks at import.

Edge cases

The same move applies to tril. Some very old code does from scipy.linalg.special_matrices import toeplitz; toeplitz stayed put, so only triu/tril need the change.