TheAlgorithms/Python · error · TypeError

Sequence must be list of non-negative integers

Error message

Sequence must be list of non-negative integers

What it means

Raised by bead_sort in sorts/bead_sort.py when any element of sequence is not an int or is negative. Bead sort physically models the numbers as beads on rods, which only works for non-negative integers, so the guard `any(not isinstance(x, int) or x < 0 for x in sequence)` rejects floats (including 0.0 and .9), strings, and negatives with a TypeError. Quirk: bool passes the check because bool is a subclass of int.

Source

Thrown at sorts/bead_sort.py:32

    >>> bead_sort([5, 0, 4, 3])
    [0, 3, 4, 5]

    >>> bead_sort([8, 2, 1])
    [1, 2, 8]

    >>> bead_sort([1, .9, 0.0, 0, -1, -.9])
    Traceback (most recent call last):
        ...
    TypeError: Sequence must be list of non-negative integers

    >>> bead_sort("Hello world")
    Traceback (most recent call last):
        ...
    TypeError: Sequence must be list of non-negative integers
    """
    if any(not isinstance(x, int) or x < 0 for x in sequence):
        raise TypeError("Sequence must be list of non-negative integers")
    for _ in range(len(sequence)):
        for i, (rod_upper, rod_lower) in enumerate(zip(sequence, sequence[1:])):  # noqa: RUF007
            if rod_upper > rod_lower:
                sequence[i] -= rod_upper - rod_lower
                sequence[i + 1] += rod_upper - rod_lower
    return sequence


if __name__ == "__main__":
    assert bead_sort([5, 4, 3, 2, 1]) == [1, 2, 3, 4, 5]
    assert bead_sort([7, 9, 4, 3, 5]) == [3, 4, 5, 7, 9]

View on GitHub (pinned to f5988cc097)

Solutions

1. Convert to non-negative ints first: bead_sort([int(x) for x in sequence]).
2. Reject or clean floats before calling: if any(not float(x).is_integer() for x in seq): ...
3. For data that may contain negatives, shift by the minimum (offset encoding) or use a comparison sort instead.

Example fix

# before
bead_sort([5.0, 3, 1])  # 5.0 is float -> TypeError

# after
bead_sort([int(x) for x in [5.0, 3, 1]])

def to_bead_input(seq):
    out = []
    for x in seq:
        if not isinstance(x, int) or isinstance(x, bool) or x < 0:
            raise TypeError(f'bead_sort needs non-negative ints, got {x!r}')
        out.append(x)
    return out

result = bead_sort(to_bead_input(data))

def is_non_negative_int_list(seq) -> bool:
    return all(
        isinstance(x, int) and not isinstance(x, bool) and x >= 0 for x in seq
    )

try:
    result = bead_sort(data)
except TypeError:
    result = bead_sort([int(x) for x in data])  # only if conversion is lossless

When it happens

Trigger: bead_sort([1, .9, 0.0, 0, -1, -.9]); bead_sort('Hello world') (iterating a string yields 1-char strs); bead_sort([3.0, 2]) where JSON parsing produced floats.

Common situations: Feeding data straight from json.load where whole numbers became floats; mixing numeric types from pandas/numpy (np.int64 is not a Python int on some platforms and will be rejected); validating user CSV input that contains blanks parsed as NaN.

Related errors

• The elements inside the sequence must contains only {colors}
• All numbers must be positive
• operation can not be conducted on an object of type {type(nu
• Input value must be an 'int' type
• plaintext must be a string

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/a3f225b22e2b54d0. Report an issue: GitHub.