pythonintegermaxsizectypes

Maximum and minimum value of C types integers from Python

I'm looking for a way to get (using Python) the maximum and minimum values of C types integers (ie `uint8`, `int8`, `uint16`, `int16`, `uint32`, `int32`, `uint64`, `int64`...) from Python.

I was expecting to find this in `ctypes` module

``````In [1]: import ctypes
In [2]: ctypes.c_uint8(256)
Out[2]: c_ubyte(0)
In [3]: ctypes.c_uint8(-1)
Out[3]: c_ubyte(255)
``````

but I couldn't find it.

Julia have great feature for this:

``````julia> typemax(UInt8)
0xff

julia> typemin(UInt8)
0x00

julia> typemin(Int8)
-128

julia> typemax(Int8)
127
``````

I'm pretty sure Python have something quite similar.

Ideally I'm even looking for a way to ensure that a given Python integer (which is said to be unbounded) can be converted safely in a C type integer of a given size. When number is not in expected interval, it should raise an exception.

Currently overflow doesn't raise exception:

``````In [4]: ctypes.c_uint8(256)
Out[4]: c_ubyte(0)
``````

I saw this SO post Maximum and Minimum values for ints but it's a bit different as author is looking for min/max value of a Python integer... not a C integer (from Python)

I also noticed Detecting C types limits ("limits.h") in python? but, even if it's quite related, it doesn't really answer my question.

Solution

• According to: [Python.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.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_short,
c_ushort,
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):
unsized_test_types = (
c_byte,
c_ubyte,
c_short,
c_ushort,
c_int,
c_uint,
c_long,
c_ulong,
c_longlong,
c_ulonglong,
)
sized_test_types = (
c_int8,
c_uint8,
c_int16,
c_uint16,
c_int32,
c_uint32,
c_int64,
c_uint64,
)
for test_types, text in (
(unsized_test_types, "Unsized types:"),
(sized_test_types, "Sized types:"),
):
print(text)
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-W10PC064:c:\Work\Dev\StackExchange\StackOverflow\q052475749]> "c:\Work\Dev\VEnvs\py_pc064_03.12_test0\Scripts\python.exe" ./code00.py
Python 3.12.2 (tags/v3.12.2:6abddd9, Feb  6 2024, 21:26:36) [MSC v.1937 64 bit (AMD64)] 064bit on win32

Unsized types:
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_longlong limits: [-9223372036854775808, 9223372036854775807]
c_ulonglong limits: [0, 18446744073709551615]
Sized types:
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_longlong limits: [-9223372036854775808, 9223372036854775807]
c_ulonglong limits: [0, 18446744073709551615]

Done.
``````
• Python pc032 (032bit):

``````[cfati@CFATI-W10PC064:c:\Work\Dev\StackExchange\StackOverflow\q052475749]> "c:\Work\Dev\VEnvs\py_pc032_03.10_test0\Scripts\python.exe" ./code00.py
Python 3.10.11 (tags/v3.10.11:7d4cc5a, Apr  5 2023, 00:20:04) [MSC v.1929 32 bit (Intel)] 032bit on win32

Unsized types:
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_longlong limits: [-9223372036854775808, 9223372036854775807]
c_ulonglong limits: [0, 18446744073709551615]
Sized types:
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_longlong limits: [-9223372036854775808, 9223372036854775807]
c_ulonglong limits: [0, 18446744073709551615]

Done.
``````
• Nix:

• Linux:

• Python pc064:

``````(py_pc064_03.08_test0_lancer) [cfati@cfati-5510-0:/mnt/e/Work/Dev/StackExchange/StackOverflow/q052475749]> python ./code00.py
Python 3.8.18 (default, Aug 25 2023, 13:20:30) [GCC 11.4.0] 064bit on linux

Unsized types:
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_long limits: [-9223372036854775808, 9223372036854775807]
c_ulong limits: [0, 18446744073709551615]
c_long limits: [-9223372036854775808, 9223372036854775807]
c_ulong limits: [0, 18446744073709551615]
Sized types:
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_long limits: [-9223372036854775808, 9223372036854775807]
c_ulong limits: [0, 18446744073709551615]

Done.
``````
• Python pc032:

``````[cfati@cfati-5510-0:/mnt/e/Work/Dev/StackExchange/StackOverflow/q052475749]> /usr/local/pc032/python/python/3.10.13/bin/python ./code00.py
Python 3.10.13 (tags/v3.10.13-dirty:49965601d6, Sep 12 2023, 19:27:34) [GCC 11.4.0] 032bit on linux

Unsized types:
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_longlong limits: [-9223372036854775808, 9223372036854775807]
c_ulonglong limits: [0, 18446744073709551615]
Sized types:
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_longlong limits: [-9223372036854775808, 9223372036854775807]
c_ulonglong limits: [0, 18446744073709551615]

Done.
``````
• OSX:

• Python pc064:

``````[cristian.fati@cfati-16i2019-0:~/Work/Dev/StackExchange/StackOverflow/q052475749]> python ./code00.py
Python 3.10.12 (main, Jun 20 2023, 17:00:24) [Clang 14.0.3 (clang-1403.0.22.14.1)] 064bit on darwin

Unsized types:
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_long limits: [-9223372036854775808, 9223372036854775807]
c_ulong limits: [0, 18446744073709551615]
c_long limits: [-9223372036854775808, 9223372036854775807]
c_ulong limits: [0, 18446744073709551615]
Sized types:
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_long limits: [-9223372036854775808, 9223372036854775807]
c_ulong limits: [0, 18446744073709551615]

Done.
``````

Notes (more or less related):