Python signatures for Java-defined methods

In essence, a method is not much different from a Java method. One defines a method as follows. Here is a simple example of a 1-argument function.

@org.python.Method(
    __doc__ = "foobar(fizz) -> buzz" +
        "\n" +
        "Return the foobarified version of fizz.\n",
    args = {"fizz"}
)
public function org.python.Object foobar(org.python.Object fizz) {
    return buzz;
}

The org.python.Method creates an annotation on the method. Allowable values are

name

The name of the method. If not specifies, uses reflection to get the name.

__doc__

The documentation string of the method.

args

An array of argument names.

varargs

The name of the argument that should get all other values.

default_args

An array of argument names that get “default” values. The handling of the default values should be done by checking the argument null`

kwonlyargs

An array of arguments that may only be supplied as a keyword argument.

kwargs

A name of the argument that recieves the keyword arguments.

Examples

Because examples speak clearer than a thousand words.

A function with no arguments

Here is a sample of a function always returning the same value. Since it has no arguments, there is no need to supply any of the named

def constant_4():
    """Return 4, always and ever."""
    return 4

@org.python.Method(
    __doc__ = "Return 4, always and ever."
)
public org.python.Object constant_4() {
    return org.python.types.Int.getInt(4);
}

A function with two arguments

Another simple function is that of adding two given numbers.

def add(num1, num2):
    """Add two numbers."""
    return num1 + num2

@org.python.Method(
    __doc__ = "Add two numbers.",
    args = {"num1", "num2"}
)
public org.python.Object add(org.python.Object num1, org.python.Object num2) {
    // Left as exercise for the reader.
}

A function with a default argument

Similarly, we might want to make the second argument optional, allowing you to either add 1 to the number, or the supplied argument.

def inc(num, delta=1):
    """Increment a number."""
    return num + delta

@org.python.Method(
    __doc__ = "Add two numbers.",
    args = {"num"},
    default_args = {"delta"}
)
public org.python.Object inc(org.python.Object num, org.python.Object delta) {
    if (delta == null) {
        delta = org.python.types.Int.getInt(1);
    }
    // Left as exercise for the reader.
}

A function with variable arguments

Of course, sometimes you don’t want to specify a specific number of arguments, but accept as many as you can get. For instance, the min function.

def min(first, *others):
    """Get the minimum of the supplied arguments."""
    val = first
    for other in others:
        if other < val:
            val = other
    return val

@org.python.Method(
    __doc__ = "Get the minimum of the supplied arguments.""",
    args = {"first"},
    varargs = "others"
)
public org.python.Object min(org.python.Object first, org.python.types.Tuple others) {
    org.python.Object val = first;
    for (org.python.Object other: others) {
        if (other.__lt__(val)) {
            val = other;
        }
    }
    return val;
}

A function accepting keyword arguments

def loop_kwargs(**kwargs):
    """Loop over the kwargs to this function."""
    for k in kwargs:
      pass

@org.python.Method(
    __doc__ = "Loop over the kwargs to this function.",
    args = {},
    kwargs = "kwargs"
)
public org.python.Object loop_kwargs(org.python.types.Dict kwargs) {
    Map<org.python.Object, org.python.Object> kwargValues = kwargs.value;
    for (org.python.Object key : kwargValues.keySet()) {
      // The keys will always be python Str objects
      org.python.types.Str keyStr = (org.python.types.Str) key;
    }
    return org.python.types.NoneType.NONE;
}