pandas-dev/pandas · error · TypeError

Expected coo_matrix. Got

Error message

Expected coo_matrix. Got {type(A).__name__} instead.

What it means

Thrown by coo_to_sparse_series in pandas/core/arrays/sparse/scipy_sparse.py:200 when the input lacks the .data/.row/.col attributes of a scipy.sparse.coo_matrix. The function wraps attribute access in try/except AttributeError and re-raises as TypeError, so any non-COO object (CSR, CSC, dense ndarray, list) is rejected with a clear message.

Solutions

1. Convert to COO first: A = A.tocoo() before calling the pandas API.
2. If starting from dense, build COO explicitly: scipy.sparse.coo_matrix(dense_arr).
3. Type-check upstream: import scipy.sparse; if not scipy.sparse.isspmatrix_coo(A): A = A.tocoo().

Example fix

// before
from scipy.sparse import csr_matrix
A = csr_matrix((3,3))
coo_to_sparse_series(A)  # raises TypeError

// after
coo_to_sparse_series(A.tocoo())

import scipy.sparse
def ensure_coo(A):
    if not scipy.sparse.isspmatrix_coo(A):
        A = A.tocoo()
    return A

import scipy.sparse
def is_coo(A) -> bool:
    return scipy.sparse.isspmatrix_coo(A)

try:
    from pandas.core.arrays.sparse.scipy_sparse import coo_to_sparse_series
    return coo_to_sparse_series(A)
except TypeError as e:
    if 'Expected coo_matrix' in str(e):
        return coo_to_sparse_series(A.tocoo())
    raise

When it happens

Trigger: Calling pd.DataFrame.sparse.from_coo(A) or the internal coo_to_sparse_series with A being a csr_matrix, csc_matrix, dense numpy array, list of lists, or a pandas DataFrame.

Common situations: User performs sparse matrix arithmetic which auto-converts COO to CSR/CSC, then feeds the result back to pandas without re-converting. Passing a dense matrix expecting implicit conversion.

Related errors

• Duplicate index entries are not allowed in to_coo…
• Is not a partition because intersection is not null.
• Is not a partition because union is not the whole.
• to_coo requires MultiIndex with nlevels >= 2.
• Column length mismatch

AI-assisted analysis of pandas-dev/pandas@3b7651241d (2026-08-11). Data as JSON: /api/errors/15cd2fb01d183d4d. Report an issue: GitHub.

Appendix: source

Thrown at pandas/core/arrays/sparse/scipy_sparse.py:200

    Parameters
    ----------
    A : scipy.sparse.coo_matrix
    dense_index : bool, default False

    Returns
    -------
    Series

    Raises
    ------
    TypeError if A is not a coo_matrix
    """
    from pandas import SparseDtype

    try:
        ser = Series(A.data, MultiIndex.from_arrays((A.row, A.col)), copy=False)
    except AttributeError as err:
        raise TypeError(
            f"Expected coo_matrix. Got {type(A).__name__} instead."
        ) from err
    ser = ser.sort_index()
    ser = ser.astype(SparseDtype(ser.dtype))
    if dense_index:
        ind = MultiIndex.from_product([A.row, A.col])
        ser = ser.reindex(ind)
    return ser

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