[NEP32 NEP34] API Cleanup and Behavioral Changes

Overview

NumPy's removal of financial functions and changes to dtype inference behavior.

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NEP 32: Remove Financial Functions

Status: Final | Full Text

Removed Functions

Function	Description
fv	Future value
pv	Present value
npv	Net present value
irr	Internal rate of return
mirr	Modified internal rate of return
nper	Number of periods
pmt	Payment
ppmt	Principal payment
ipmt	Interest payment
rate	Rate of return

Rationale

• Too specialized for NumPy's core mission
• Cannot handle actual dates/calendars
• Low usage (only 8 GitHub repos found)
• Little maintainer interest

Timeline

• NumPy 1.18: Deprecated with warnings
• NumPy 1.20: Removed

Replacement

numpy-financial package on PyPI.

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NEP 34: Disallow Inferring dtype=object

Status: Final | Full Text

Behavior Change

Before (NumPy 1.x)

# Silent object dtype for ragged sequences
np.array([[1, 2], [1]])
# array([[1, 2], [1]], dtype=object)

After (NumPy 2.x)

# Raises ValueError
np.array([[1, 2], [1]])
# ValueError: cannot guess the desired dtype

Cases That Raise

# Ragged sequences
np.array([[1, 2], [1]])

# Mixed sequences and non-sequences
np.array([np.arange(10), [10]])

# Mixed types within sequences
np.array([[range(3), range(3)], [range(3), 0]])

Explicit dtype=object

# Still works when explicit
np.array([[1, 2], [1]], dtype=object)

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Suggested Implementation for NumSharp

Financial Functions

DO NOT IMPLEMENT. These are outside NumSharp's scope. Users needing financial calculations should use dedicated C# libraries.

dtype=object Inference

Ragged Sequence Detection

public static NDArray array(object input, NPTypeCode? dtype = null) {
    if (IsRaggedSequence(input)) {
        if (dtype == NPTypeCode.Object) {
            // Explicit request - allow
            return CreateObjectArray(input);
        }
        throw new ValueError(
            "Cannot guess dtype from ragged sequence. " +
            "Use dtype=object explicitly.");
    }
    // Normal array creation
}

private static bool IsRaggedSequence(object input) {
    // Check if nested sequences have mismatched lengths
    if (input is IEnumerable outer) {
        int? expectedLength = null;
        foreach (var item in outer) {
            if (item is IEnumerable inner) {
                int len = inner.Cast<object>().Count();
                if (expectedLength == null) {
                    expectedLength = len;
                } else if (len != expectedLength) {
                    return true;  // Ragged
                }
            }
        }
    }
    return false;
}

Dead Code Audit

Per CLAUDE.md, these functions need attention:

Function	Current State	Action
np.linalg.norm	private static	Make public or remove
nd.inv()	returns null	Throw NotImplementedException
nd.qr()	returns default	Throw NotImplementedException
nd.svd()	returns default	Throw NotImplementedException
nd.lstsq()	returns null	Throw NotImplementedException
np.isnan	returns null	Implement or throw
np.isfinite	returns null	Implement or throw
np.isclose	returns null	Implement or throw
operator &	returns null	Implement or throw
operator |	returns null	Implement or throw

Buggy Functions

Function	Issue	Fix
np.any with axis	Always throws	Fix implementation
nd.roll()	Limited types	Extend to all types
Boolean mask setter	NotImplementedException	Implement

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Documentation

See docs/neps/NEP32.md, docs/neps/NEP34.md