TheAlgorithms/Python · error · TypeError

number of qubits must be a integer.

Error message

number of qubits must be a integer.

What it means

Raised by quantum_fourier_transform() in quantum/q_fourier_transform.py when number_of_qubits is a str. The guard exists because string input (e.g. "3") would otherwise fail later comparisons with a confusing TypeError; only the str type is singled out here, other non-numeric types fall through to the <= comparison and raise Python's own TypeError.

Source

Thrown at quantum/q_fourier_transform.py:59

    >>> quantum_fourier_transform(-1)
    Traceback (most recent call last):
        ...
    ValueError: number of qubits must be > 0.
    >>> quantum_fourier_transform('a')
    Traceback (most recent call last):
        ...
    TypeError: number of qubits must be a integer.
    >>> quantum_fourier_transform(100)
    Traceback (most recent call last):
        ...
    ValueError: number of qubits too large to simulate(>10).
    >>> quantum_fourier_transform(0.5)
    Traceback (most recent call last):
        ...
    ValueError: number of qubits must be exact integer.
    """
    if isinstance(number_of_qubits, str):
        raise TypeError("number of qubits must be a integer.")
    if number_of_qubits <= 0:
        raise ValueError("number of qubits must be > 0.")
    if math.floor(number_of_qubits) != number_of_qubits:
        raise ValueError("number of qubits must be exact integer.")
    if number_of_qubits > 10:
        raise ValueError("number of qubits too large to simulate(>10).")

    qr = QuantumRegister(number_of_qubits, "qr")
    cr = ClassicalRegister(number_of_qubits, "cr")

    quantum_circuit = QuantumCircuit(qr, cr)

    counter = number_of_qubits

    for i in range(counter):
        quantum_circuit.h(number_of_qubits - i - 1)
        counter -= 1
        for j in range(counter):

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass a numeric value: quantum_fourier_transform(3).
2. Convert string inputs before calling: int(num_qubits_str) (with its own error handling).
3. Use argparse type=int or pydantic/FastAPI int annotations to coerce at the boundary.

Example fix

# before
nq = request.args.get('qubits')  # "3"
quantum_fourier_transform(nq)  # TypeError

# after
nq = int(request.args.get('qubits'))
quantum_fourier_transform(nq)

if isinstance(number_of_qubits, str):
    number_of_qubits = int(number_of_qubits)  # let ValueError propagate on bad text
quantum_fourier_transform(number_of_qubits)

def is_numeric_qubit_count(value) -> bool:
    return not isinstance(value, str) and isinstance(value, (int, float))

try:
    qc = quantum_fourier_transform(nq)
except TypeError as e:
    if "must be a integer" in str(e):
        qc = quantum_fourier_transform(int(nq))
    else:
        raise

When it happens

Trigger: quantum_fourier_transform("3"), quantum_fourier_transform("ten"). Any value arriving as text from CLI args, config files, or HTTP query parameters without conversion.

Common situations: argparse without type=int; YAML/JSON config values quoted as strings; REST endpoints passing query params as strings into the function.

Related errors

• Parameter number must be int
• Parameters chain_length and number_limit must be int
• degrees must be a numeric value between 0 and 360.
• length must be a positive numeric value.
• Expected a matrix, got int/list instead

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/80387b9d4a39602c. Report an issue: GitHub.