How to Determine if Your Python is 32-bit or 64-bit

Knowing whether your Python interpreter is running in 32-bit or 64-bit mode is important for various reasons, such as compatibility with libraries, memory usage, and performance.

This guide presents reliable and cross-platform methods to determine your Python's "bitness" both from the command line and within Python scripts.

Checking Bitness from the Command Line (Cross-Platform)

The most reliable and concise way to check your Python's bitness from the command line (works on Windows, macOS, and Linux) is to use the -c option to execute a short Python command directly:

python -c "import sys; print(sys.maxsize > 2**32)"

• python -c: This tells Python to execute the following string as a Python command. You might need to use python3 or py instead of python depending on your system.
• import sys: Imports the sys module, which provides access to system-specific parameters and functions.
• print(sys.maxsize > 2**32): This is the core check. sys.maxsize returns the maximum value a variable of type Py_ssize_t can take. This value is significantly larger on 64-bit systems than on 32-bit systems. We compare it to 2**32 (which is 2 raised to the power of 32, a key boundary between 32-bit and 64-bit addressing).
  • If the output is True, you're running 64-bit Python.
  • If the output is False, you're running 32-bit Python.

Checking Bitness Within a Python Script

You can perform the same check within a Python script:

Using sys.maxsize (Recommended)

import sys

is_64bits = sys.maxsize > 2**32
print(is_64bits)

if is_64bits:
    print('Python is running as 64-bit application')
else:
    print('Python is running as 32-bit application')

This is the method officially recommended in the Python documentation. It's concise, clear, and works reliably across all major operating systems.

Using struct.calcsize()

Another cross-platform method involves the struct module, which is used for packing and unpacking binary data:

import struct

print(struct.calcsize('P') * 8)  # Output: 32 or 64

if struct.calcsize('P') * 8 == 64:
    print('Python is running as 64-bit application')
else:
    print('Python is running as 32-bit application')

• struct.calcsize('P'): This returns the size (in bytes) of a native pointer on your system. 'P' is a format character representing a "void *" (a generic pointer). On 32-bit systems, pointers are 4 bytes; on 64-bit systems, they are 8 bytes.
• * 8: We multiply by 8 to convert from bytes to bits.

Windows-Specific Method (Informational)

On Windows, you can sometimes determine the bitness by inspecting the output when you start the Python interpreter in the command prompt:

Python 3.9.7 (tags/v3.9.7:1016ef3, Aug 30 2021, 20:19:38) [MSC v.1929 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>

Look for text similar to "[MSC v.1929 64 bit (AMD64)]". However, this is NOT a reliable method for use within a script; it's purely for informational purposes when interacting with the interpreter directly.

Why platform.architecture() is Unreliable on macOS (and some other platforms)

You might encounter examples using platform.architecture():

import platform

print(platform.architecture()[0])  # Output might be '64bit'