1.5. Compiling code ahead of time

While Numba’s main use case is Just-in-Time compilation, it also provides a facility for Ahead-of-Time compilation (AOT).

1.5.1. Overview

1.5.1.1. Benefits

  1. AOT compilation produces a compiled extension module which does not depend on Numba: you can distribute the module on machines which do not have Numba installed (but Numpy is required).
  2. There is no compilation overhead at runtime (but see the @jit cache option), nor any overhead of importing Numba.

See also

Compiled extension modules are discussed in the Python packaging user guide.

1.5.1.2. Limitations

  1. AOT compilation only allows for regular functions, not ufuncs.
  2. You have to specify function signatures explicitly.
  3. Each exported function can have only one signature (but you can export several different signatures under different names).
  4. AOT compilation produces generic code for your CPU’s architectural family (for example “x86-64”), while JIT compilation produces code optimized for your particular CPU model.

1.5.2. Usage

1.5.2.1. Standalone example

from numba.pycc import CC

cc = CC('my_module')
# Uncomment the following line to print out the compilation steps
#cc.verbose = True

@cc.export('multf', 'f8(f8, f8)')
@cc.export('multi', 'i4(i4, i4)')
def mult(a, b):
    return a * b

@cc.export('square', 'f8(f8)')
def square(a):
    return a ** 2

if __name__ == "__main__":
    cc.compile()

If you run this Python script, it will generate an extension module named my_module. Depending on your platform, the actual filename may be my_module.so, my_module.pyd, my_module.cpython-34m.so, etc.

The generated module has three functions: multf, multi and square. multi operates on 32-bit integers (i4), while multf and square operate on double-precision floats (f8):

>>> import my_module
>>> my_module.multi(3, 4)
12
>>> my_module.square(1.414)
1.9993959999999997

1.5.2.2. Distutils integration

You can also integrate the compilation step for your extension modules in your setup.py script, using distutils or setuptools:

from distutils.core import setup

from source_module import cc

setup(...,
      ext_modules=[cc.distutils_extension()])

The source_module above is the module defining the cc object. Extensions compiled like this will be automatically included in the build files for your Python project, so you can distribute them inside binary packages such as wheels or Conda packages.

1.5.2.3. Signature syntax

The syntax for exported signatures is the same as in the @jit decorator. You can read more about it in the types reference.

Here is an example of exporting an implementation of the second-order centered difference on a 1d array:

@cc.export('centdiff_1d', 'f8[:](f8[:], f8)')
def centdiff_1d(u, dx):
    D = np.empty_like(u)
    D[0] = 0
    D[-1] = 0
    for i in range(1, len(D) - 1):
        D[i] = (u[i+1] - 2 * u[i] + u[i-1]) / dx**2
    return D