TheAlgorithms/Python · error · TypeError

Expected a string as input

Error message

Expected a string as input

What it means

Raised by octal_to_hex() in conversions/octal_to_hexadecimal.py when the `octal` argument is not a str instance. The function's contract is string-only input; ints, floats, None, or bytes all hit the isinstance check and raise TypeError immediately.

Source

Thrown at conversions/octal_to_hexadecimal.py:25

    '0x40'
    >>> octal_to_hex("235")
    '0x9D'
    >>> octal_to_hex(17)
    Traceback (most recent call last):
        ...
    TypeError: Expected a string as input
    >>> octal_to_hex("Av")
    Traceback (most recent call last):
        ...
    ValueError: Not a Valid Octal Number
    >>> octal_to_hex("")
    Traceback (most recent call last):
        ...
    ValueError: Empty string was passed to the function
    """

    if not isinstance(octal, str):
        raise TypeError("Expected a string as input")
    if octal.startswith("0o"):
        octal = octal[2:]
    if octal == "":
        raise ValueError("Empty string was passed to the function")
    if any(char not in "01234567" for char in octal):
        raise ValueError("Not a Valid Octal Number")

    decimal = 0
    for char in octal:
        decimal <<= 3
        decimal |= int(char)

    hex_char = "0123456789ABCDEF"

    revhex = ""
    while decimal:
        revhex += hex_char[decimal & 15]
        decimal >>= 4

View on GitHub (pinned to f5988cc097)

Solutions

1. Convert to str first: octal_to_hex(str(value)) when value is an int.
2. Fix the upstream loader to keep the field as a string (e.g. dtype=str when reading CSV).
3. Add an isinstance(octal, str) check at the call site for untrusted data.

Example fix

# before
octal_to_hex(777)  # TypeError: Expected a string as input

# after
octal_to_hex(str(777))  # '1FF'

if not isinstance(octal, str):
    octal = str(octal)  # or reject: raise TypeError from your own layer
octal_to_hex(octal)

def is_octal_str(octal: object) -> bool:
    return isinstance(octal, str) and all(c in '01234567' for c in octal.removeprefix('0o'))

try:
    octal_to_hex(value)
except TypeError as e:
    if 'Expected a string' in str(e):
        value = str(value)
        result = octal_to_hex(value)
    else:
        raise

When it happens

Trigger: Calling octal_to_hex(777) with an int, octal_to_hex(None), octal_to_hex(b'777'), or passing a value that came from a JSON number field.

Common situations: Assuming the converter accepts integers like int(octal_string, 8) would; reading mixed-type data (API responses, CSV columns) where the field is sometimes numeric; passing a default None when a lookup fails.

Related errors

• Non-octal value was passed to the function
• Not a Valid Octal Number
• Expected int, found {type(r_input), type(g_input), type(b_in
• operation can not be conducted on an object of type {type(nu
• Input value must be an 'int' type

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/742bcec46e1496c1. Report an issue: GitHub.