Python Functionality

Extension Types (Classes)

Numba supports classes similar to Python classes and extension types. Currently the methods have static signatures, but in the future they we will likely support multiple inheritance and autojitting methods.

One can refer to the extension type as a type by accessing its exttype attribute:

@jit
class MyExtension(object):
    ...

@jit(MyExtension.exttype(double))
def create_ext(arg):
    return MyExtension(arg)

It is not yet possible to refer to the extension type in the class body or methods of that extension type.

An example of extension classes and their capabilities and limitations is shown below:

# -*- coding: utf-8 -*-
"""
Example for extension classes.

Things that work:

    - overriding Numba methods in Numba (all methods are virtual)
    - inheritance
    - instance attributes
    - subclassing in python and calling overridden methods in Python
    - arbitrary new attributes on extension classes and objects
    - weakrefs to extension objects

Things that do NOT (yet) work:

    - overriding methods in Python and calling the method from Numba
    - multiple inheritance of Numba classes
        (multiple inheritance with Python classes should work)
    - subclassing variable sized objects like 'str' or 'tuple'
"""
from __future__ import print_function, division, absolute_import

from numba import jit, void, int_, double

# All methods must be given signatures

@jit
class Shrubbery(object):
    @void(int_, int_)
    def __init__(self, w, h):
        # All instance attributes must be defined in the initializer
        self.width = w
        self.height = h

        # Types can be explicitly specified through casts
        self.some_attr = double(1.0)

    @int_()
    def area(self):
        return self.width * self.height

    @void()
    def describe(self):
        print("This shrubbery is ", self.width,
              "by", self.height, "cubits.")
 
shrub = Shrubbery(10, 20)
print(shrub.area())
shrub.describe()
print(shrub.width, shrub.height)
shrub.width = 30
print(shrub.area())
print(shrub._numba_attrs._fields_) # This is an internal attribute subject to change!

class MyClass(Shrubbery):
    def newmethod(self):
        print("This is a new method.")

shrub2 = MyClass(30,40)
shrub2.describe()
shrub2.newmethod()
print(shrub._numba_attrs._fields_)

Closures

Numba supports closures (nested functions), and keeps the variable scopes alive for the lifetime of the closures. Variables that are closed over by the closures (cell variables) have one consistent type throughout the entirety of the function. This means differently typed variables can only be assigned if they are unifyable, such as for instance ints and floats:

@autojit
def outer(arg1, arg2):
    arg1 = 0
    arg1 = 0.0      # This is fine
    arg1 = "hello"  # ERROR! arg1 must have a single type

    arg2 = 0
    arg2 = "hello"  # FINE! Not a cell variable

    def inner():
        print arg1

    return inner

Calling an inner function directly in the body of outer will result in a direct, native call of the closure. In the future it is likely that passing around the closure will still result in a native call in other places.

Like Python closures, closures can be arbitrarily nested, and follow the same scoping rules.

Typed Containers

Numba ships implementations of various typed containers, which allow fast execution and memory-efficient storage.

We hope to support the following container types:

• list, tuple
• dict, ordereddict
• set, orderedset
• queues, channels
• <your idea here>

There are many more data structure that can be implemented, but future releases of numba will make it easier (nearly trivial) for people to implement those data structure themselves while supporting full data polymorphism.

Currently implemented:

• typedlist
• typedtuple

These data structures work exactly like their python equivalents, but take a first parameter which specifies the element type:

>>> numba.typedlist(int32, range(10))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> numba.typedlist(float32, range(10))
[0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0]

>>> tlist = numba.typedlist(int32)
>>> tlist
[]
>>> tlist.extend([3, 2, 1, 3])
>>> tlist
[3, 1, 2, 3]
>>> tlist.count(3)
2L
>>> tlist[0]
3L
>>> tlist.pop()
3L
>>> tlist.reverse()
>>> tlist
[1, 2, 3]

Things that are not yet implemented:

• Methods remove, insert
• Slicing

Typed containers can be used from Python or from numba code. Using them from numba code will result in fast calls without boxing and unboxing.