Maximum and minimum value of C types integers from Python

According to: [Python 3 docs]: Numeric Types – int, float, complex:

Integers have unlimited precision.

Translated to code:

>>> i = 10 ** 100
>>> i
10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
>>> len(str(i))
101
>>> i.bit_length()
333

On the other hand, each C type has a fixed size (depending on platform / architecture), as clearly shown in [CPPReference]: Fundamental types.

Since [Python 3 docs]: ctypes – A foreign function library for Python doesn’t mention anything about types limits (note that there is some stuff not documented there), let’s find them out manually.

code00.py:

#!/usr/bin/env python3

import sys
from ctypes import c_int8, c_uint8, c_byte, c_ubyte, c_int16, c_uint16, \
    c_int32, c_uint32, c_int, c_uint, c_long, c_ulong, c_longlong, c_ulonglong, \
    c_int64, c_uint64, \
    sizeof


def limits(c_int_type):
    signed = c_int_type(-1).value < c_int_type(0).value
    bit_size = sizeof(c_int_type) * 8
    signed_limit = 2 ** (bit_size - 1)
    return (-signed_limit, signed_limit - 1) if signed else (0, 2 * signed_limit - 1)


def main(*argv):
    test_types = (
        c_int8,
        c_uint8,
        c_byte,
        c_ubyte,
        c_int16,
        c_uint16,
        c_int32,
        c_uint32,
        c_int,
        c_uint,
        c_long,
        c_ulong,
        c_longlong,
        c_ulonglong,
        c_int64,
        c_uint64,
    )
    for test_type in test_types:
        print("{:s} limits: ({:d}, {:d})".format(test_type.__name__, *limits(test_type)))


if __name__ == "__main__":
    print("Python {:s} {:03d}bit on {:s}\n".format(" ".join(elem.strip() for elem in sys.version.split("\n")),
                                                   64 if sys.maxsize > 0x100000000 else 32, sys.platform))
    rc = main(*sys.argv[1:])
    print("\nDone.")
    sys.exit(rc)

Notes:

Code relies on the fact that for a certain integral type, its interval (and limits are interval’s endpoints) is:
- signed _{(2‘s complement)}: [-(2 ^{bit_size – 1}), 2 ^{bit_size – 1} – 1]
- unsigned: [0, 2 ^bit_size – 1]
To check the a type’s signum, use -1 (which will automatically be converted to the upper limit (due to wrap around arithmetic) by unsigned types)
There are lots of duplicates the output (below), because some types are simply “aliases” to others
The rest of your task (creating a function that compares a Python int to the CTypes type limits, and raises an exception if it isn’t) is trivial, so I didn’t implement it
This is for demonstrating purpose only, so I didn’t do any argument check

Output:

Win:

Python pc064 (064bit):

[cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q052475749]> "e:\Work\Dev\VEnvs\py_pc064_03.09_test0\Scripts\python.exe" ./code00.py
Python 3.9.9 (tags/v3.9.9:ccb0e6a, Nov 15 2021, 18:08:50) [MSC v.1929 64 bit (AMD64)] 064bit on win32

c_byte limits: (-128, 127)
c_ubyte limits: (0, 255)
c_byte limits: (-128, 127)
c_ubyte limits: (0, 255)
c_short limits: (-32768, 32767)
c_ushort limits: (0, 65535)
c_long limits: (-2147483648, 2147483647)
c_ulong limits: (0, 4294967295)
c_long limits: (-2147483648, 2147483647)
c_ulong limits: (0, 4294967295)
c_long limits: (-2147483648, 2147483647)
c_ulong limits: (0, 4294967295)
c_longlong limits: (-9223372036854775808, 9223372036854775807)
c_ulonglong limits: (0, 18446744073709551615)
c_longlong limits: (-9223372036854775808, 9223372036854775807)
c_ulonglong limits: (0, 18446744073709551615)

Done.

Python pc032 (032bit):

[cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q052475749]> "e:\Work\Dev\VEnvs\py_pc032_03.10_test0\Scripts\python.exe" ./code00.py
Python 3.10.1 (tags/v3.10.1:2cd268a, Dec  6 2021, 18:54:59) [MSC v.1929 32 bit (Intel)] 032bit on win32

c_byte limits: (-128, 127)
c_ubyte limits: (0, 255)
c_byte limits: (-128, 127)
c_ubyte limits: (0, 255)
c_short limits: (-32768, 32767)
c_ushort limits: (0, 65535)
c_long limits: (-2147483648, 2147483647)
c_ulong limits: (0, 4294967295)
c_long limits: (-2147483648, 2147483647)
c_ulong limits: (0, 4294967295)
c_long limits: (-2147483648, 2147483647)
c_ulong limits: (0, 4294967295)
c_longlong limits: (-9223372036854775808, 9223372036854775807)
c_ulonglong limits: (0, 18446744073709551615)
c_longlong limits: (-9223372036854775808, 9223372036854775807)
c_ulonglong limits: (0, 18446744073709551615)

Done.

Nix (Linux – WSL2) – Python pc064:

(qaic-env) [cfati@cfati-5510-0:/mnt/e/Work/Dev/StackOverflow/q052475749]> python ./code00.py
Python 3.8.10 (default, Mar 15 2022, 12:22:08) [GCC 9.4.0] 064bit on linux

c_byte limits: (-128, 127)
c_ubyte limits: (0, 255)
c_byte limits: (-128, 127)
c_ubyte limits: (0, 255)
c_short limits: (-32768, 32767)
c_ushort limits: (0, 65535)
c_int limits: (-2147483648, 2147483647)
c_uint limits: (0, 4294967295)
c_int limits: (-2147483648, 2147483647)
c_uint limits: (0, 4294967295)
c_long limits: (-9223372036854775808, 9223372036854775807)
c_ulong limits: (0, 18446744073709551615)
c_long limits: (-9223372036854775808, 9223372036854775807)
c_ulong limits: (0, 18446744073709551615)
c_long limits: (-9223372036854775808, 9223372036854775807)
c_ulong limits: (0, 18446744073709551615)

Done.

Note (more or less related): Many people encounter problems when calling functions via CTypes. Mentioning [SO]: C function called from Python via ctypes returns incorrect value (@CristiFati’s answer) just in case.

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