# API and ABI Versioning

## Build-time version constants

CPython exposes its version number in the following macros. Note that these correspond to the version code is built with. See `Py_Version` for the version used at run time.

See C API Stability for a discussion of API and ABI stability across versions.

PY_MAJOR_VERSION

  The `3` in `3.4.1a2`.

PY_MINOR_VERSION

  The `4` in `3.4.1a2`.

PY_MICRO_VERSION

  The `1` in `3.4.1a2`.

PY_RELEASE_LEVEL

  The `a` in `3.4.1a2`. This can be `0xA` for alpha, `0xB` for beta, `0xC` for release candidate or `0xF` for final.

PY_RELEASE_SERIAL

  The `2` in `3.4.1a2`. Zero for final releases.

PY_VERSION_HEX

  The Python version number encoded in a single integer. See `Py_PACK_FULL_VERSION()` for the encoding details.

  Use this for numeric comparisons, for example, `#if PY_VERSION_HEX >= ...`.

These macros are defined in Include/patchlevel.h.

## Run-time version

const unsigned long Py_Version
  Part of the Stable ABI since version 3.11.

  The Python runtime version number encoded in a single constant integer. See `Py_PACK_FULL_VERSION()` for the encoding details. This contains the Python version used at run time.

  Use this for numeric comparisons, for example, `if (Py_Version >= ...)`.

  Added in version 3.11.

## Bit-packing macros

uint32_t Py_PACK_FULL_VERSION(int major, int minor, int micro, int release_level, int release_serial)
  Part of the Stable ABI since version 3.14.

  Return the given version, encoded as a single 32-bit integer with the following structure:

  Argument | No. of bits | Bit mask | Bit shift | Example values
  --- | --- | --- | --- | ---
  `3.4.1a2` | `3.10.0`
  major | 8 | `0xFF000000` | 24 | `0x03` | `0x03`
  minor | 8 | `0x00FF0000` | 16 | `0x04` | `0x0A`
  micro | 8 | `0x0000FF00` | 8 | `0x01` | `0x00`
  release_level | 4 | `0x000000F0` | 4 | `0xA` | `0xF`
  release_serial | 4 | `0x0000000F` | 0 | `0x2` | `0x0`

  For example:

  Version | `Py_PACK_FULL_VERSION` arguments | Encoded version
  --- | --- | ---
  `3.4.1a2` | `(3, 4, 1, 0xA, 2)` | `0x030401a2`
  `3.10.0` | `(3, 10, 0, 0xF, 0)` | `0x030a00f0`

  Out-of range bits in the arguments are ignored. That is, the macro can be defined as:

      #ifndef Py_PACK_FULL_VERSION
      #define Py_PACK_FULL_VERSION(X, Y, Z, LEVEL, SERIAL) ( \
         (((X) & 0xff) << 24) |                              \
         (((Y) & 0xff) << 16) |                              \
         (((Z) & 0xff) << 8) |                               \
         (((LEVEL) & 0xf) << 4) |                            \
         (((SERIAL) & 0xf) << 0))
      #endif

  `Py_PACK_FULL_VERSION` is primarily a macro, intended for use in `#if` directives, but it is also available as an exported function.

  Added in version 3.14.

uint32_t Py_PACK_VERSION(int major, int minor)
  Part of the Stable ABI since version 3.14.

  Equivalent to `Py_PACK_FULL_VERSION(major, minor, 0, 0, 0)`. The result does not correspond to any Python release, but is useful in numeric comparisons.

  Added in version 3.14.