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).
Overview¶
Benefits¶
- 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).
- 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.
Limitations¶
- AOT compilation only allows for regular functions, not ufuncs.
- You have to specify function signatures explicitly.
- Each exported function can have only one signature (but you can export several different signatures under different names).
- 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.
Usage¶
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
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. Note that in the case of
using conda, the compilers used for AOT need to be those that are available
in the Anaconda distribution.
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
You can also omit the return type, which will then be inferred by Numba:
@cc.export('centdiff_1d', '(f8[:], f8)')
def centdiff_1d(u, dx):
# Same code as above
...