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Added doco for abstract interface

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Guido van Rossum 1996-08-09 21:01:07 +00:00
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files). No \samp{-l} options can be used.
\input{extref}
\input{ext.ind}
\end{document}

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files). No \samp{-l} options can be used.
\input{extref}
\input{ext.ind}
\end{document}

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\section{Extension Reference}
From the viewpoint of of C access to Python services, we have:
\begin{enumerate}
\item "Very high level layer": two or three functions that let you exec or
eval arbitrary Python code given as a string in a module whose name is
given, passing C values in and getting C values out using
mkvalue/getargs style format strings. This does not require the user
to declare any variables of type "PyObject *". This should be enough
to write a simple application that gets Python code from the user,
execs it, and returns the output or errors.
\item "Abstract objects layer": which is the subject of this proposal.
It has many functions operating on objects, and lest you do many
things from C that you can also write in Python, without going
through the Python parser.
\item "Concrete objects layer": This is the public type-dependent
interface provided by the standard built-in types, such as floats,
strings, and lists. This interface exists and is currently
documented by the collection of include files provides with the
Python distributions.
From the point of view of Python accessing services provided by C
modules:
\item "Python module interface": this interface consist of the basic
routines used to define modules and their members. Most of the
current extensions-writing guide deals with this interface.
\item "Built-in object interface": this is the interface that a new
built-in type must provide and the mechanisms and rules that a
developer of a new built-in type must use and follow.
\end{enumerate}
The Python C object interface provides four protocols: object,
numeric, sequence, and mapping. Each protocol consists of a
collection of related operations. If an operation that is not
provided by a particular type is invoked, then a standard exception,
NotImplementedError is raised with a operation name as an argument.
In addition, for convenience this interface defines a set of
constructors for building objects of built-in types. This is needed
so new objects can be returned from C functions that otherwise treat
objects generically.
\subsubsection{Object Protocol}
\code{int *PyObject_Print(PyObject *o, FILE *fp, int flags)}\\
Print an object \code{o}, on file \code{fp}. Returns -1 on error
The flags argument is used to enable certain printing
options. The only option currently supported is \code{Py_Print_RAW}.
\code{int PyObject_HasAttrString(PyObject *o, char *attr_name)}\\
Returns 1 if o has the attribute attr_name, and 0 otherwise.
This is equivalent to the Python expression:
\code{hasattr(o,attr_name)}.
This function always succeeds.
\code{PyObject* PyObject_AttrString(PyObject *o, char *attr_name)}\\
Retrieve an attributed named attr_name form object o.
Returns the attribute value on success, or NULL on failure.
This is the equivalent of the Python expression: \code{o.attr_name}.
\code{int PyObject_HasAttr(PyObject *o, PyObject *attr_name)}\\
Returns 1 if o has the attribute attr_name, and 0 otherwise.
This is equivalent to the Python expression:
\code{hasattr(o,attr_name)}.
This function always succeeds.
\code{PyObject* PyObject_GetAttr(PyObject *o, PyObject *attr_name)}\\
Retrieve an attributed named attr_name form object o.
Returns the attribute value on success, or NULL on failure.
This is the equivalent of the Python expression: o.attr_name.
\code{int PyObject_SetAttrString(PyObject *o, char *attr_name, PyObject *v)}\\
Set the value of the attribute named \code{attr_name}, for object \code{o},
to the value \code{v}. Returns -1 on failure. This is
the equivalent of the Python statement: \code{o.attr_name=v}.
\code{int PyObject_SetAttr(PyObject *o, PyObject *attr_name, PyObject *v)}\\
Set the value of the attribute named \code{attr_name}, for object \code{o},
to the value \code{v}. Returns -1 on failure. This is
the equivalent of the Python statement: \code{o.attr_name=v}.
\code{int PyObject_DelAttrString(PyObject *o, char *attr_name)}\\
Delete attribute named \code{attr_name}, for object \code{o}. Returns -1 on
failure. This is the equivalent of the Python
statement: \code{del o.attr_name}.
\code{int PyObject_DelAttr(PyObject *o, PyObject *attr_name)}\\
Delete attribute named \code{attr_name}, for object \code{o}. Returns -1 on
failure. This is the equivalent of the Python
statement: \code{del o.attr_name}.
\code{int PyObject_Cmp(PyObject *o1, PyObject *o2, int *result)}\\
Compare the values of \code{o1} and \code{o2} using a routine provided by
\code{o1}, if one exists, otherwise with a routine provided by \code{o2}.
The result of the comparison is returned in \code{result}. Returns
-1 on failure. This is the equivalent of the Python
statement: \code{result=cmp(o1,o2)}.
\code{int PyObject_Compare(PyObject *o1, PyObject *o2)}\\
Compare the values of \code{o1} and \code{o2} using a routine provided by
\code{o1}, if one exists, otherwise with a routine provided by \code{o2}.
Returns the result of the comparison on success. On error,
the value returned is undefined. This is equivalent to the
Python expression: \code{cmp(o1,o2)}.
\code{PyObject *PyObject_Repr(PyObject *o)}\\
Compute the string representation of object, \code{o}. Returns the
string representation on success, NULL on failure. This is
the equivalent of the Python expression: \code{repr(o)}.
Called by the \code{repr()} built-in function and by reverse quotes.
\code{PyObject *PyObject_Str(PyObject *o)}\\
Compute the string representation of object, \code{o}. Returns the
string representation on success, NULL on failure. This is
the equivalent of the Python expression: \code{str(o)}.
Called by the \code{str()} built-in function and by the \code{print}
statement.
\code{int *PyCallable_Check(PyObject *o))}\\
Determine if the object \code{o}, is callable. Return 1 if the
object is callable and 0 otherwise.
This function always succeeds.
\code{PyObject *PyObject_CallObject(PyObject *callable_object, PyObject *args)}\\
Call a callable Python object \code{callable_object}, with
arguments given by the tuple \code{args}. If no arguments are
needed, then args may be NULL. Returns the result of the
call on success, or NULL on failure. This is the equivalent
of the Python expression: \code{apply(o,args)}.
\code{PyObject *PyObject_CallFunction(PyObject *callable_object, char *format, ...)}\\
Call a callable Python object \code{callable_object}, with a
variable number of C arguments. The C arguments are described
using a mkvalue-style format string. The format may be NULL,
indicating that no arguments are provided. Returns the
result of the call on success, or NULL on failure. This is
the equivalent of the Python expression: \code{apply(o,args)}.
\code{PyObject *PyObject_CallMethod(PyObject *o, char *m, char *format, ...)}\\
Call the method named \code{m} of object \code{o} with a variable number of
C arguments. The C arguments are described by a mkvalue
format string. The format may be NULL, indicating that no
arguments are provided. Returns the result of the call on
success, or NULL on failure. This is the equivalent of the
Python expression: \code{o.method(args)}.
Note that Special method names, such as "\code{__add__}",
"\code{__getitem__}", and so on are not supported. The specific
abstract-object routines for these must be used.
\code{int PyObject_Hash(PyObject *o)}\\
Compute and return the hash value of an object \code{o}. On
failure, return -1. This is the equivalent of the Python
expression: \code{hash(o)}.
\code{int *PyObject_IsTrue(PyObject *o)}\\
Returns 1 if the object \code{o} is considered to be true, and
0 otherwise. This is equivalent to the Python expression:
\code{not not o}.
This function always succeeds.
\code{PyObject *PyObject_Type(PyObject *o)}\\
On success, returns a type object corresponding to the object
type of object \code{o}. On failure, returns NULL. This is
equivalent to the Python expression: \code{type(o)}.
\code{int PyObject_Length(PyObject *o)}\\
Return the length of object \code{o}. If the object \code{o} provides
both sequence and mapping protocols, the sequence length is
returned. On error, -1 is returned. This is the equivalent
to the Python expression: \code{len(o)}.
\code{PyObject *PyObject_GetItem(PyObject *o, PyObject *key)}\\
Return element of \code{o} corresponding to the object \code{key} or NULL
on failure. This is the equivalent of the Python expression:
\code{o[key]}.
\code{int PyObject_SetItem(PyObject *o, PyObject *key, PyObject *v)}\\
Map the object \code{key} to the value \code{v}.
Returns -1 on failure. This is the equivalent
of the Python statement: \code{o[key]=v}.
\subsubsection{Number Protocol}
\code{int PyNumber_Check(PyObject *o)}\\
Returns 1 if the object \code{o} provides numeric protocols, and
false otherwise.
This function always succeeds.
\code{PyObject *PyNumber_Add(PyObject *o1, PyObject *o2)}\\
Returns the result of adding \code{o1} and \code{o2}, or null on failure.
This is the equivalent of the Python expression: \code{o1+o2}.
\code{PyObject *PyNumber_Subtract(PyObject *o1, PyObject *o2)}\\
Returns the result of subtracting \code{o2} from \code{o1}, or null on
failure. This is the equivalent of the Python expression:
\code{o1-o2}.
\code{PyObject *PyNumber_Multiply(PyObject *o1, PyObject *o2)}\\
Returns the result of multiplying \code{o1} and \code{o2}, or null on
failure. This is the equivalent of the Python expression:
\code{o1*o2}.
\code{PyObject *PyNumber_Divide(PyObject *o1, PyObject *o2)}\\
Returns the result of dividing \code{o1} by \code{o2}, or null on failure.
This is the equivalent of the Python expression: \code{o1/o2}.
\code{PyObject *PyNumber_Remainder(PyObject *o1, PyObject *o2)}\\
Returns the remainder of dividing \code{o1} by \code{o2}, or null on
failure. This is the equivalent of the Python expression:
\code{o1\%o2}.
\code{PyObject *PyNumber_Divmod(PyObject *o1, PyObject *o2)}\\
See the built-in function divmod. Returns NULL on failure.
This is the equivalent of the Python expression:
\code{divmod(o1,o2)}.
\code{PyObject *PyNumber_Power(PyObject *o1, PyObject *o2, PyObject *o3)}\\
See the built-in function pow. Returns NULL on failure.
This is the equivalent of the Python expression:
\code{pow(o1,o2,o3)}, where \code{o3} is optional.
\code{PyObject *PyNumber_Negative(PyObject *o)}\\
Returns the negation of \code{o} on success, or null on failure.
This is the equivalent of the Python expression: \code{-o}.
\code{PyObject *PyNumber_Positive(PyObject *o)}\\
Returns \code{o} on success, or NULL on failure.
This is the equivalent of the Python expression: \code{+o}.
\code{PyObject *PyNumber_Absolute(PyObject *o)}\\
Returns the absolute value of \code{o}, or null on failure. This is
the equivalent of the Python expression: \code{abs(o)}.
\code{PyObject *PyNumber_Invert(PyObject *o)}\\
Returns the bitwise negation of \code{o} on success, or NULL on
failure. This is the equivalent of the Python expression:
\code{~o}.
\code{PyObject *PyNumber_Lshift(PyObject *o1, PyObject *o2)}\\
Returns the result of left shifting \code{o1} by \code{o2} on success, or
NULL on failure. This is the equivalent of the Python
expression: \code{o1 << o2}.
\code{PyObject *PyNumber_Rshift(PyObject *o1, PyObject *o2)}\\
Returns the result of right shifting \code{o1} by \code{o2} on success, or
NULL on failure. This is the equivalent of the Python
expression: \code{o1 >> o2}.
\code{PyObject *PyNumber_And(PyObject *o1, PyObject *o2)}\\
Returns the result of "anding" \code{o2} and \code{o2} on success and NULL
on failure. This is the equivalent of the Python
expression: \code{o1 and o2}.
\code{PyObject *PyNumber_Xor(PyObject *o1, PyObject *o2)}\\
Returns the bitwise exclusive or of \code{o1} by \code{o2} on success, or
NULL on failure. This is the equivalent of the Python
expression: \code{o1\^{ }o2}.
\code{PyObject *PyNumber_Or(PyObject *o1, PyObject *o2)}\\
Returns the result or \code{o1} and \code{o2} on success, or NULL on
failure. This is the equivalent of the Python expression:
\code{o1 or o2}.
\code{PyObject *PyNumber_Coerce(PyObject *o1, PyObject *o2)}\\
On success, returns a tuple containing \code{o1} and \code{o2} converted to
a common numeric type, or None if no conversion is possible.
Returns -1 on failure. This is equivalent to the Python
expression: \code{coerce(o1,o2)}.
\code{PyObject *PyNumber_Int(PyObject *o)}\\
Returns the \code{o} converted to an integer object on success, or
NULL on failure. This is the equivalent of the Python
expression: \code{int(o)}.
\code{PyObject *PyNumber_Long(PyObject *o)}\\
Returns the \code{o} converted to a long integer object on success,
or NULL on failure. This is the equivalent of the Python
expression: \code{long(o)}.
\code{PyObject *PyNumber_Float(PyObject *o)}\\
Returns the \code{o} converted to a float object on success, or NULL
on failure. This is the equivalent of the Python expression:
\code{float(o)}.
\subsubsection{Sequence protocol}
\code{int PySequence_Check(PyObject *o)}\\
Return 1 if the object provides sequence protocol, and 0
otherwise.
This function always succeeds.
\code{PyObject *PySequence_Concat(PyObject *o1, PyObject *o2)}\\
Return the concatination of \code{o1} and \code{o2} on success, and NULL on
failure. This is the equivalent of the Python
expression: \code{o1+o2}.
\code{PyObject *PySequence_Repeat(PyObject *o, int count)}\\
Return the result of repeating sequence object \code{o} count times,
or NULL on failure. This is the equivalent of the Python
expression: \code{o*count}.
\code{PyObject *PySequence_GetItem(PyObject *o, int i)}\\
Return the ith element of \code{o}, or NULL on failure. This is the
equivalent of the Python expression: \code{o[i]}.
\code{PyObject *PySequence_GetSlice(PyObject *o, int i1, int i2)}\\
Return the slice of sequence object \code{o} between \code{i1} and \code{i2}, or
NULL on failure. This is the equivalent of the Python
expression, \code{o[i1:i2]}.
\code{int PySequence_SetItem(PyObject *o, int i, PyObject *v)}\\
Assign object \code{v} to the \code{i}th element of \code{o}.
Returns -1 on failure. This is the equivalent of the Python
statement, \code{o[i]=v}.
\code{int PySequence_SetSlice(PyObject *o, int i1, int i2, PyObject *v)}\\
Assign the sequence object \code{v} to the slice in sequence
object \code{o} from \code{i1} to \code{i2}. This is the equivalent of the Python
statement, \code{o[i1:i2]=v}.
\code{PyObject *PySequence_Tuple(PyObject *o)}\\
Returns the \code{o} as a tuple on success, and NULL on failure.
This is equivalent to the Python expression: \code{tuple(o)}.
\code{int PySequence_Count(PyObject *o, PyObject *value)}\\
Return the number of occurrences of \code{value} on \code{o}, that is,
return the number of keys for which \code{o[key]==value}. On
failure, return -1. This is equivalent to the Python
expression: \code{o.count(value)}.
\code{int PySequence_In(PyObject *o, PyObject *value)}\\
Determine if \code{o} contains \code{value}. If an item in \code{o} is equal to
\code{value}, return 1, otherwise return 0. On error, return -1. This
is equivalent to the Python expression: \code{value in o}.
\code{int PySequence_Index(PyObject *o, PyObject *value)}\\
Return the first index for which \code{o[i]=value}. On error,
return -1. This is equivalent to the Python
expression: \code{o.index(value)}.
\subsubsection{Mapping protocol}
\code{int PyMapping_Check(PyObject *o)}\\
Return 1 if the object provides mapping protocol, and 0
otherwise.
This function always succeeds.
\code{int PyMapping_Length(PyObject *o)}\\
Returns the number of keys in object \code{o} on success, and -1 on
failure. For objects that do not provide sequence protocol,
this is equivalent to the Python expression: \code{len(o)}.
\code{int PyMapping_DelItemString(PyObject *o, char *key)}\\
Remove the mapping for object \code{key} from the object \code{o}.
Return -1 on failure. This is equivalent to
the Python statement: \code{del o[key]}.
\code{int PyMapping_DelItem(PyObject *o, PyObject *key)}\\
Remove the mapping for object \code{key} from the object \code{o}.
Return -1 on failure. This is equivalent to
the Python statement: \code{del o[key]}.
\code{int PyMapping_HasKeyString(PyObject *o, char *key)}\\
On success, return 1 if the mapping object has the key \code{key}
and 0 otherwise. This is equivalent to the Python expression:
\code{o.has_key(key)}.
This function always succeeds.
\code{int PyMapping_HasKey(PyObject *o, PyObject *key)}\\
Return 1 if the mapping object has the key \code{key}
and 0 otherwise. This is equivalent to the Python expression:
\code{o.has_key(key)}.
This function always succeeds.
\code{PyObject *PyMapping_Keys(PyObject *o)}\\
On success, return a list of the keys in object \code{o}. On
failure, return NULL. This is equivalent to the Python
expression: \code{o.keys()}.
\code{PyObject *PyMapping_Values(PyObject *o)}\\
On success, return a list of the values in object \code{o}. On
failure, return NULL. This is equivalent to the Python
expression: \code{o.values()}.
\code{PyObject *PyMapping_Items(PyObject *o)}\\
On success, return a list of the items in object \code{o}, where
each item is a tuple containing a key-value pair. On
failure, return NULL. This is equivalent to the Python
expression: \code{o.items()}.
\code{int PyMapping_Clear(PyObject *o)}\\
Make object \code{o} empty. Returns 1 on success and 0 on failure.
This is equivalent to the Python statement:
\code{for key in o.keys(): del o[key]}
\code{PyObject *PyMapping_GetItemString(PyObject *o, char *key)}\\
Return element of \code{o} corresponding to the object \code{key} or NULL
on failure. This is the equivalent of the Python expression:
\code{o[key]}.
\code{PyObject *PyMapping_SetItemString(PyObject *o, char *key, PyObject *v)}\\
Map the object \code{key} to the value \code{v} in object \code{o}. Returns
-1 on failure. This is the equivalent of the Python
statement: \code{o[key]=v}.
\subsubsection{Constructors}
\code{PyObject *PyFile_FromString(char *file_name, char *mode)}\\
On success, returns a new file object that is opened on the
file given by \code{file_name}, with a file mode given by \code{mode},
where \code{mode} has the same semantics as the standard C routine,
fopen. On failure, return -1.
\code{PyObject *PyFile_FromFile(FILE *fp, char *file_name, char *mode, int close_on_del)}\\
Return a new file object for an already opened standard C
file pointer, \code{fp}. A file name, \code{file_name}, and open mode,
\code{mode}, must be provided as well as a flag, \code{close_on_del}, that
indicates whether the file is to be closed when the file
object is destroyed. On failure, return -1.
\code{PyObject *PyFloat_FromDouble(double v)}\\
Returns a new float object with the value \code{v} on success, and
NULL on failure.
\code{PyObject *PyInt_FromLong(long v)}\\
Returns a new int object with the value \code{v} on success, and
NULL on failure.
\code{PyObject *PyList_New(int l)}\\
Returns a new list of length \code{l} on success, and NULL on
failure.
\code{PyObject *PyLong_FromLong(long v)}\\
Returns a new long object with the value \code{v} on success, and
NULL on failure.
\code{PyObject *PyLong_FromDouble(double v)}\\
Returns a new long object with the value \code{v} on success, and
NULL on failure.
\code{PyObject *PyDict_New()}\\
Returns a new empty dictionary on success, and NULL on
failure.
\code{PyObject *PyString_FromString(char *v)}\\
Returns a new string object with the value \code{v} on success, and
NULL on failure.
\code{PyObject *PyString_FromStringAndSize(char *v, int l)}\\
Returns a new string object with the value \code{v} and length \code{l}
on success, and NULL on failure.
\code{PyObject *PyTuple_New(int l)}\\
Returns a new tuple of length \code{l} on success, and NULL on
failure.