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Predicate py_call/3 |
Arguments to Python functions use the Python conventions. Both
positional and keyword arguments are supported. Keyword
arguments are written as Name = Value
and must appear after the
positional arguments.
Below are some examples.
% call a built-in ?- py_call(print("Hello World!\n")). true. % call a built-in (alternative) ?- py_call(builtins:print("Hello World!\n")). true. % call function in a module ?- py_call(sys:getsizeof([1,2,3]), Size). Size = 80. % call function on an attribute of a module ?- py_call(sys:path:append("/home/bob/janus")). true % get attribute from a module ?- py_call(sys:path, Path) Path = ["dir1", "dir2", ...]
Given a class in a file dog.py
such as the following example from
the Python documentation
class Dog: tricks = [] def __init__(self, name): self.name = name def add_trick(self, trick): self.tricks.append(trick)
We can interact with this class as below. Note that $Doc
in the
SWI-Prolog toplevel refers to the last toplevel binding for the
variable Dog.
?- py_call(dog:'Dog'("Fido"), Dog). Dog = <py_Dog>(0x7f095c9d02e0). ?- py_call($Dog:add_trick("roll_over")). Dog = <py_Dog>(0x7f095c9d02e0). ?- py_call($Dog:tricks, Tricks). Dog = <py_Dog>(0x7f095c9d02e0), Tricks = ["roll_over"]
If the principal term of the first argument is not Target:Func
,
The argument is evaluated as the initial target, i.e., it must be an
object reference or a module. For example:
?- py_call(dog:'Dog'("Fido"), Dog), py_call(Dog, X). Dog = X, X = <py_Dog>(0x7fa8cbd12050). ?- py_call(sys, S). S = <py_module>(0x7fa8cd582390).
Options processed:
true
(default false
), translate the return as a Python
object reference. Some objects are always translated to
Prolog, regardless of this flag. These are the Python constants
None
, True
and False
as well as instances of the
Python base classes int
, float
, str
or tuple
. Instances
of sub classes of these base classes are controlled by this
option.atom
(default), translate a Python String into a
Prolog atom. If Type is string
, translate into a Prolog string.
Strings are more efficient if they are short lived.dict
(default) to map a Python dict to a SWI-Prolog
dict if all keys can be represented. If {}
or not all keys
can be represented, Return is unified to a term {k:v, ...}
or py({})
if the Python dict is empty.py_string_as
and py_dict_as
are
SWI-Prolog specific, where SWI-Prolog Janus represents Python
strings as atoms as required by the PIP and it represents Python
dicts by default as SWI-Prolog dicts. The predicates values/3,
keys/2, etc. provide portable access to the data in the dict.