擴充/嵌入常見問題集
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我可以在 C 中建立自己的函式嗎？
===============================

是的，你可以在 C 中建立包含函式、變數、例外甚至新型別的內建模組，擴充
和嵌入 Python 直譯器 文件中有相關說明。

大多數中級或進階 Python 書籍也會涵蓋這個主題。


我可以在 C++ 中建立自己的函式嗎？
=================================

是的，可使用 C++ 中的 C 相容性功能。將 "extern "C" { ... }" 放在
Python 引入檔案周圍，並將 "extern "C"" 放在每個將由 Python 直譯器呼叫
的函式之前。但具有構造函式的全域或靜態 C++ 物件可能不是一個好主意。


寫 C 很難；還有其他選擇嗎？
===========================

There are a number of alternatives to writing your own C extensions,
depending on what you're trying to do. Recommended third party tools
offer both simpler and more sophisticated approaches to creating C and
C++ extensions for Python.


如何從 C 執行任意 Python 陳述式？
=================================

The highest-level function to do this is "PyRun_SimpleString()" which
takes a single string argument to be executed in the context of the
module "__main__" and returns "0" for success and "-1" when an
exception occurred (including "SyntaxError").  If you want more
control, use "PyRun_String()"; see the source for
"PyRun_SimpleString()" in "Python/pythonrun.c".


How can I evaluate an arbitrary Python expression from C?
=========================================================

Call the function "PyRun_String()" from the previous question with the
start symbol "Py_eval_input"; it parses an expression, evaluates it
and returns its value.


如何從 Python 物件中提取 C 值？
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That depends on the object's type.  If it's a tuple, "PyTuple_Size()"
returns its length and "PyTuple_GetItem()" returns the item at a
specified index.  Lists have similar functions, "PyList_Size()" and
"PyList_GetItem()".

For bytes, "PyBytes_Size()" returns its length and
"PyBytes_AsStringAndSize()" provides a pointer to its value and its
length.  Note that Python bytes objects may contain null bytes so C's
"strlen()" should not be used.

要測試物件的型別，首先確保它不是 "NULL"，然後再使用 "PyBytes_Check()"
、"PyTuple_Check()"、"PyList_Check()" 等函式。

There is also a high-level API to Python objects which is provided by
the so-called 'abstract' interface -- read "Include/abstract.h" for
further details.  It allows interfacing with any kind of Python
sequence using calls like "PySequence_Length()",
"PySequence_GetItem()", etc. as well as many other useful protocols
such as numbers ("PyNumber_Index()" et al.) and mappings in the
PyMapping APIs.


如何使用 Py_BuildValue() 建立任意長度的元組？
=============================================

這無法做到。請改用 "PyTuple_Pack()"。


如何從 C 呼叫物件的方法？
=========================

The "PyObject_CallMethod()" function can be used to call an arbitrary
method of an object.  The parameters are the object, the name of the
method to call, a format string like that used with "Py_BuildValue()",
and the argument values:

   PyObject *
   PyObject_CallMethod(PyObject *object, const char *method_name,
                       const char *arg_format, ...);

這適用於任何具有方法的物件 —— 無論是內建的還是使用者定義的。你負責最終
為回傳值來 "Py_DECREF()"。

例如，使用引數 10、0 呼叫檔案物件的 "seek" 方法（假設檔案物件指標為
"f"）：

   res = PyObject_CallMethod(f, "seek", "(ii)", 10, 0);
   if (res == NULL) {
           ... 發生一個例外 ...
   }
   else {
           Py_DECREF(res);
   }

請注意，由於 "PyObject_CallObject()" *總是*需要一個元組作為引數列表，
若要呼叫一個不帶引數的函式，要傳遞 "()" 作為格式，並呼叫一個帶有一個引
數的函式，將引數括起來在括號中，例如 "(i)"。


我如何捕捉 PyErr_Print() 的輸出（或任何印出到 stdout/stderr 的東西）？
======================================================================

In Python code, define an object that supports the "write()" method.
Assign this object to "sys.stdout" and "sys.stderr".  Call
print_error, or just allow the standard traceback mechanism to work.
Then, the output will go wherever your "write()" method sends it.

最簡單的方法是使用 "io.StringIO" 類別：

   >>> import io, sys
   >>> sys.stdout = io.StringIO()
   >>> print('foo')
   >>> print('hello world!')
   >>> sys.stderr.write(sys.stdout.getvalue())
   foo
   hello world!

執行相同操作的自定義物件如下所示：

   >>> import io, sys
   >>> class StdoutCatcher(io.TextIOBase):
   ...     def __init__(self):
   ...         self.data = []
   ...     def write(self, stuff):
   ...         self.data.append(stuff)
   ...
   >>> import sys
   >>> sys.stdout = StdoutCatcher()
   >>> print('foo')
   >>> print('hello world!')
   >>> sys.stderr.write(''.join(sys.stdout.data))
   foo
   hello world!


如何從 C 存取用 Python 編寫的模組？
===================================

你可以取得指向模組物件的指標，如下所示：

   module = PyImport_ImportModule("<modulename>");

如果模組還沒有被引入（即它還沒有出現在 "sys.modules" 中），這會初始化
模組；否則它只回傳 "sys.modules["<modulename>"]" 的值。請注意，它不會
將模組輸入任何命名空間——它只會確保它已被初始化並儲存在 "sys.modules"
中。

然後你可以存取模組的屬性（即模組中定義的任何名稱），如下所示：

   attr = PyObject_GetAttrString(module, "<attrname>");

Calling "PyObject_SetAttrString()" to assign to variables in the
module also works.


我如何從 Python 介接到 C++ 物件？
=================================

根據你的要求不同而有多種不同方法。要手動執行此操作，請先閱讀「擴充和嵌
入」說明文件。對於 Python run-time 系統，C 和 C++ 之間並沒有太多區別
—— 因此圍繞 C 結構（指標）型別來構建新 Python 型別的策略也適用於 C++
物件。

對於 C++ 函式庫，請參閱 寫 C 很難；還有其他選擇嗎？。


我使用安裝檔案新增了一個模組，但 make 失敗了；為什麼？
======================================================

Setup must end in a newline, if there is no newline there, the build
process fails.  (Fixing this requires some ugly shell script hackery,
and this bug is so minor that it doesn't seem worth the effort.)


如何為擴充套件除錯？
====================

When using GDB with dynamically loaded extensions, you can't set a
breakpoint in your extension until your extension is loaded.

在你的 ".gdbinit" 檔案中（或交互地），新增命令：

   br _PyImport_LoadDynamicModule

然後，當你運行 GDB 時：

   $ gdb /local/bin/python
   gdb) run myscript.py
   gdb) continue # repeat until your extension is loaded
   gdb) finish   # so that your extension is loaded
   gdb) br myfunction.c:50
   gdb) continue


我想在我的 Linux 系統上編譯一個 Python 模組，但是缺少一些檔案。為什麼？
=======================================================================

Most packaged versions of Python omit some files required for
compiling Python extensions.

在 Red Hat 上，請安裝 python3-devel RPM 來取得必要的檔案。

對於 Debian，運行 "apt-get install python3-dev"。


如何從「無效輸入」區分出「不完整輸入」？
========================================

Sometimes you want to emulate the Python interactive interpreter's
behavior, where it gives you a continuation prompt when the input is
incomplete (e.g. you typed the start of an "if" statement or you
didn't close your parentheses or triple string quotes), but it gives
you a syntax error message immediately when the input is invalid.

在 Python 中，你可以使用 "codeop" 模組，它充分模擬了剖析器 (parser) 的
行為。像是 IDLE 就有使用它。

The easiest way to do it in C is to call "PyRun_InteractiveLoop()"
(perhaps in a separate thread) and let the Python interpreter handle
the input for you. You can also set the
"PyOS_ReadlineFunctionPointer()" to point at your custom input
function. See "Modules/readline.c" and "Parser/myreadline.c" for more
hints.


如何找到未定義的 g++ 符號 __builtin_new 或 __pure_virtual？
===========================================================

To dynamically load g++ extension modules, you must recompile Python,
relink it using g++ (change LINKCC in the Python Modules Makefile),
and link your extension module using g++ (e.g., "g++ -shared -o
mymodule.so mymodule.o").


我可以用一些用 C 實作的方法和用 Python 實作的其他方法（例如透過繼承）建立一個物件類別嗎？
=========================================================================================

是的，你可以繼承內建類別，例如 "int"、"list"、"dict" 等。

Boost Python 函式庫（BPL，
https://www.boost.org/libs/python/doc/index.html）提供了一種從 C++ 執
行此操作的方法（即你可以使用 BPL 來繼承用 C++ 編寫的擴充類別）。
