What is Pycaml
A library written by
arty@users.sourceforge.net which follows the Python/C API as
closely as possible, while
providing equivalent functionality for objective caml. This is built
against python 2.x and Ocaml 3.04. It is intended to allow users to
build native ocaml libraries and use them from python, and alternately,
in order to allow ocaml users to benefit from linkable libraries provided
for python.
I created this library in order to take advantage of python binding for
certain native libraries from ocaml. While it is true that I could have
written new interfaces specifically for ocaml, the python interface is
sufficient for my needs, and this project was easier.
Note: Unfortunately, the symbol init_exceptions exists in
both compiled ocaml code, and the python runtime. In order to proceed, you
must rename this symbol either in the ocaml distribution (in byterun/fail.c,
and byterun/startup.c), or in the python distribution, and rebuild the
software appropriately.
Please edit the Makefile to put in your system's libraries used for
compiling programs embedded with python. This library compiles on most
linux boxes without modification. The python interpreter is used to determine
the path to the python library and must be in your path when you run make.
Get the distribution here:pycaml.tar.gz
Because these are made to closely mirror the python API, the user should
become familiar with the python API.
Given Ocaml parameter passing convention, it was convenient to pass multiple
arguments as members of a tuple, but single arguments without. Consequently,
functions with arity 1, such as pytuple_new are called as
pytuple_new 3 ;;
And functions with more arguments are called as
pydict_getitemstring (dict,"keystring") ;;
Module Pycaml
Visible Types
type | pyobject |
The abstract type of python objects.
|
type | pyobject_type = |
| TupleType |
| | StringType |
| | IntType |
| | FloatType |
| | ListType |
| | NoneType |
| | CallableType |
| | ModuleType |
| | ClassType |
| | TypeType |
| | OtherType |
The type representing the range of types available to python programs.
Values of this type are provided by the pytype function, and identify the
python type of opaque pyobject objects.
|
Supported Functions from the Python/C API
In each case, the signature of the function is unchanged from the Python/C
API except for the case of 'out' pointer to pointer parameters;
in the case of a single return, the returned value is copied, otherwise,
a tuple is created with copies of all output parameters. In the case of
zero parameter, or void return, unit is used.
In python API functions that take a FILE *, an int file descriptor is used
instead such as those returned by the Unix library.
fun unit -> unit
py_initialize, py_finalize, pyerr_print, pyerr_clear, pyimport_cleanup
fun int -> unit
py_exit, pyerr_printex
fun string -> unit
py_setprogramname, py_setpythonhome
fun unit -> int
py_isinitialized, pyeval_getrestricted
fun string -> int
pyrun_simplestring, pyimport_importfrozenmodule,
fun (int * string) -> int
pyrun_anyfile, pyrun_simplefile, pyrun_interactiveone, pyrun_interactiveloop,
py_fdisinteractive
fun (int * string * int) -> int
pyrun_anyfileex, pyrun_simplefileex
fun unit -> string
py_getprogramname, py_getpthonhome, py_getprogramfullpath, py_getprefix,
py_getexecprefix, py_getpath, py_getversion, py_getplatform, py_getcopyright,
py_getcompiler, py_getbuildinfo
fun (string * int * pyobject * pyobject) -> pyobject
pyrun_string
fun (int * string * int * pyobject * pyobject) -> pyobject
pyrun_file
fun (int * string * int * pyobject * pyobject * int) -> pyobject
pyrun_fileex
fun (string * string * int) -> pyobject
py_compilestring
fun (pyobject * int * int) -> int
pyobject_print, pytuple_getslice, pysequence_getslice
fun pyobject -> pyobject
pyobject_repr, pyobject_str, pyobject_unicode, pydict_keys, pydict_values,
pydict_items, pydict_copy, pymodule_getdict, pymethod_function, pymethod_self,
pymethod_class, pymodule_getdict, pyimport_reloadmodule, pyobject_type,
pynumber_negative, pynumber_positive, pynumber_absolute, pynumber_invert,
pynumber_int, pynumber_long, pynumber_float, pysequence_tuple, pysequence_list
fun (pyobject * pyobject * int) -> pyobject
pyobject_richcompare
fun (pyobject * string) -> pyobject
pyobject_getattrstring, pydict_getitemstring, pysequence_fast,
pymapping_haskeystring, pymapping_getitemstring
fun (pyobject * pyobject) -> pyobject
pyobject_getattr, pystring_format, pydict_getitem, pyinstance_newraw,
pyeval_callobject, pyobject_getitem, pyobject_delitem, pynumber_add,
pynumber_subtract, pynumber_multiply, pynumber_divide, pynumber_remainder,
pynumber_divmod, pynumber_lshift, pynumber_rshift, pynumber_and, pynumber_xor,
pynumber_or, pynumber_inplaceadd, pynumber_inplacesubtract, pynumber_inplacemultiply, pynumber_inplacedivide, pynumber_inplaceremainder, pynumber_inplacelshift, pynumber_inplacershift, pynumber_inplaceand, pynumber_inplacexor, pynumber_inplaceor, pysequence_concat, pysequence_inplaceconcat
fun pyobject -> int
pyobject_istrue, pyobject_not, pycalable_check, pystring_size, pydict_size,
pytuple_new, pyerr_exceptionmatches, pyobject_size, pynumber_check,
pysequence_check, pysequence_size, pysequence_length, pymapping_check,
pymapping_size, pymapping_length, pyint_asint
fun (pyobject * pyobject) -> int
pyobject_compare, pyobject_hasattr, pydict_delitem,
pyerr_givenexceptionmatches, pysequence_count, pysequence_contains,
pysequence_in, pysequence_index, pymapping_haskey
fun (pyobject * pyobject * int) -> int
pyobject_richcomparebool, pysequence_delitem
fun (pyobject * string * pyobject) -> int
pyobject_setattrstring, pydict_setitemstring
fun (pyobject * string) -> int
pyobject_hasattrstring, pydict_delitemstring, pysequence_inplacerepeat
fun (pyobject * pyobject) -> (pyobject * pyobject)
pynumber_coerce, pynumber_coerceex
fun (pyobject * pyobject * pyobject) -> int
pyobject_setattr, pydict_setitem, pyobject_setitem
fun pyobject -> int64
pyobject_hash, pyint_aslong
fun pyobject -> string
pystring_asstring, pymodule_getname, pymodule_getfilename
fun (pyobject * pyobject) -> pyobject
pystring_concat, pystring_concatanddel
fun string -> pyobject
pystring_fromstring, pymodule_new, pyimport_addmodule, pyimport_importmodule,
pyimport_import
fun unit -> pyobject
pydict_new, pyerr_occurred, pyimport_getmoduledict, pyeval_getbuiltins,
pyeval_getglobals, pyeval_getlocals, pyeval_getframe
fun pyobject -> unit
pydict_clear, pyerr_setnone
fun (pyobject * int) -> (pyobject * pyobject * int)
pydict_next
fun int64 -> pyobject
pyint_fromlong
fun unit -> int64
pyint_getmax
fun float -> pyobject
pyfloat_fromdouble
fun pyobject -> float
pyfloat_asdouble
fun int -> pyobject
pytuple_new, pyint_fromint
fun (pyobject * int) -> pyobject
pytuple_getitem, pysequence_repeat, pysequence_getitem
fun (pyobject * int * pyobject) -> int
pytuple_setitem, pysequence_setitem, pymapping_setitem
fun (pyobject * pyobject * pyobject) -> pyobject
pyslice_new, pyclass_new, pyinstance_new, pymethod_new,
pyeval_callobjectwithkeywords, pynumber_power, pynumber_inplacepower
fun (pyobject * int) -> (int * int * int)
pyslice_getindices
fun (int * int * int * int) -> pyobject
pyrange_new
fun (pyobject * pyobject) -> unit
pyerr_setobject
fun (pyobject * string) -> unit
pyerr_setstring
fun (pyobject * pyobject * pyobject) -> (pyobject * pyobject * pyobject)
pyerr_fetch, pyerr_normalizeexception
fun (pyobject * pyobject * pyobject) -> unit
pyerr_restore
fun (pyobject * string) -> pyobject
pyimport_execcodemodule
fun (string * pyobject * string) -> pyobject
pyimport_execcodemoduleex
fun (string * pyobject * pyobject * pyobject) -> pyobject
pyimport_importmoduleex
fun pyobject -> string
pyobject_ascharbuffer, pyobject_asreadbuffer, pyobject_aswritebuffer
fun (pyobject * int * int * pyobject) -> int
pysequence_setslice
fun (pyobject * int * int) -> int
pysequence_delslice
Unique Functions Needed for Ocaml
In addition to the functions in the usual library, several new functions are
provided which give specific support for ocaml.
pytuple_toarray |
pyobject -> pyobject array |
Convert a python tuple to an ocaml array containing the same items.
|
pywrap_closure | (pyobject -> pyobject) -> pyobject |
Create a python callable object from a closure. The closure receives the
argument tuple from the invocation and returns a pyobject.
|
pywrap_value | 'a -> pyobject |
Create a simple void * style wrapping around an ocaml object. The object
may be retrieved with pyunwrap_value : pyobject -> 'a. Use this
to enclose an ocaml data structure in python to be used later.
|
pynull | unit -> pyobject |
Generate the null PyObject * and return it. This may sound dangerous, but
it is used by library calls to indicate errors to the python system.
|
pynone | unit -> pyobject |
Generate a reference to the Py_None object.
|
pytuple_fromarray |
pyobject array -> pyobject |
Create a pytuple (as would be used for a function call) from the given
array. This may be used to implement varargs calls on python functions,
and for other purposes.
|
pytuple_empty |
pyobject array -> pyobject |
Shortcut for pytuple_new 0
|
pytuple_fromsingle |
pyobject -> pyobject |
Create a tuple with the single given object inside. Use this to create
single element tuples as for a function call with one argument.
|
pytuple1-5 |
(pyobject * ...) -> pyobject |
Create a python tuple that has the same contents as the given ocaml tuple.
|
pytype |
pyobject -> pyobject_type |
Determine roughly which type family the given value belongs to. For example,
pytype (pystring_fromstring "hi") yields StringType.
|
Sample Application
This is the sample application that I developed the library with. It
illustrates a python function call, as well as a call back into ocaml.
The first form is used in cases where python libraries are to be used
from ocaml, and the second would be used to produce native libraries in
ocaml.
open Pycaml ;;
let colorsys = pyimport_importmodule "colorsys"
let dict = pymodule_getdict colorsys
let triplet = pytuple3 (pyfloat_fromdouble 1.0,
pyfloat_fromdouble 0.5,
pyfloat_fromdouble 0.2) ;;
let rgbtoyiq = pydict_getitemstring (dict,"rgb_to_yiq")
let triplet = pyeval_callobject (rgbtoyiq,triplet)
let _ = print_endline ((string_of_float
(pyfloat_asdouble (pytuple_getitem (triplet,0)))) ^
" " ^
(string_of_float
(pyfloat_asdouble (pytuple_getitem (triplet,1)))) ^
" " ^
(string_of_float
(pyfloat_asdouble (pytuple_getitem (triplet,2))))) ;;
let x = pywrap_closure
(fun x -> print_string (pystring_asstring (pytuple_getitem (x,0))) ;
pynone ())
let _ = pyeval_callobject
(x,pytuple_fromsingle (pystring_fromstring "hi there"))