Python/C：一次解析所有值以返回Python？

Question

如果您将大量值从 C 输出到 Python 中的字典，是否有比以下更好（更快且不易出错）的方法：

    return Py_BuildValue("{s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:d,s:(i,i,i,i),s:(i,i,i,i),s:(i,i,i,i)}",
            "jd\0",             spa.jd, //Julian day
            "jc\0",             spa.jc, //Julian century
            "jde\0",            spa.jde, //Julian ephemeris day
            "jce\0",            spa.jce, //Julian ephemeris century
            "jme\0",            spa.jme, //Julian ephemeris millennium
            "l\0",              spa.l, //earth heliocentric longitude [degrees]
            "b\0",              spa.b, //earth heliocentric latitude [degrees]
            "r\0",              spa.r,     //earth radius vector [Astronomical Units, AU]
            "theta\0",          spa.theta, //geocentric longitude [degrees]
            "beta\0",           spa.beta, //geocentric latitude [degrees]
            "x0\0",             spa.x0, //mean elongation (moon-sun) [degrees]
            "x1\0",             spa.x1, //mean anomaly (sun) [degrees]
            "x2\0",             spa.x2, //mean anomaly (moon) [degrees]
            "x3\0",             spa.x3, //argument latitude (moon) [degrees]
            "x4\0",             spa.x4, //ascending longitude (moon) [degrees]
            "del_psi\0",        spa.del_psi, //nutation longitude [degrees]
            "del_epsilon\0",    spa.del_epsilon, //nutation obliquity [degrees]
            "epsilon0\0",       spa.epsilon0, //ecliptic mean obliquity [arc seconds]
            "epsilon\0",        spa.epsilon, //ecliptic true obliquity  [degrees]
            "del_tau\0",        spa.del_tau, //aberration correction [degrees]
            "lamda\0",          spa.lamda, //apparent sun longitude [degrees]
            "nu0\0",            spa.nu0, //Greenwich mean sidereal time [degrees]
            "nu\0",             spa.nu, //Greenwich sidereal time [degrees]
            "alpha\0",          spa.alpha, //geocentric sun right ascension [degrees]
            "delta\0",          spa.delta, //geocentric sun declination [degrees]
            "h\0",              spa.h, //observer hour angle [degrees]
            "xi\0",             spa.xi, //sun equatorial horizontal parallax [degrees]
            "del_alpha\0",      spa.del_alpha, //sun right ascension parallax [degrees]
            "delta_prime\0",    spa.delta_prime, //topocentric sun declination [degrees]
            "alpha_prime\0",    spa.alpha_prime, //topocentric sun right ascension [degrees]
            "h_prime\0",        spa.h_prime, //topocentric local hour angle [degrees],
            "h0_prime\0",       spa.h0_prime,
            "delta_zero\0",     spa.delta_zero,
            "e0\0",             spa.e0, //topocentric elevation angle (uncorrected) [degrees]
            "del_e\0",          spa.del_e, //atmospheric refraction correction [degrees]
            "e\0",              spa.e, //topocentric elevation angle (corrected) [degrees]
            "eot\0",            spa.eot, //equation of time [minutes]
            "srha\0",           spa.srha, //sunrise hour angle [degrees]
            "ssha\0",           spa.ssha, //sunset hour angle [degrees]
            "sta\0",            spa.sta, //sun transit altitude [degrees]
            "zenith\0",         spa.zenith, //topocentric zenith angle [degrees]
            "azimuth180\0",     spa.azimuth180, //topocentric azimuth angle (westward from south) [-180 to 180 degrees]
            "azimuth\0",        spa.azimuth, //topocentric azimuth angle (eastward from north) [   0 to 360 degrees]
            "incidence\0",      spa.incidence, //surface incidence angle [degrees]
            "_suntransit\0",    spa.suntransit, //local sun transit time (or solar noon) [fractional hour]
            "_sunrise\0",       spa.sunrise, //local sunrise time (+/- 30 seconds) [fractional hour]
            "_sunset\0",        spa.sunset, //local sunset time (+/- 30 seconds) [fractional hour]
            "sunrise\0",        sunrise_hour, sunrise_min, sunrise_sec, sunrise_microsec,
            "sunset\0",         sunset_hour, sunset_min, sunset_sec, sunset_microsec,
            "noon\0",           transit_hour, transit_min, transit_sec, transit_microsec
            );

Answer 1

我同意 @Martin v. Löwis 关于使用 C 预处理器及其宏功能来减轻至少一些设置和维护类似您正在做的事情的负担的观点。如果正确定义这些宏，则可以将所有定义信息安排在单个头文件的单个位置中，并避免重复。

基本上，您需要有关每个物品或钥匙和钥匙的两条信息。将进入您正在构建的字典的值对。第一部分是 Py_BuildValue() 格式字符串参数中的内容，第二部分是键及其关联值的来源。

您可以通过定义然后重新定义任务所需使用的宏来提取这两组信息中的每一个。对于您的示例，可以创建以下头文件。请注意，两组不同的宏中的一组是如何定义的，具体取决于 #include 时定义的是 FORMAT 还是 FIELDS。

// builddict.h -- for defining Py_BuildValue() arguments

// define apppropriate macros for current usage
#ifdef FORMAT
    #define SPA_FIELD_LAST(FIELD)           "s:d"
    #define SPA_FIELD(FIELD)                SPA_FIELD_LAST(FIELD)", "
    #define TIME_FIELD_LAST(NAME)           "s:(i,i,i,i)"
    #define TIME_FIELD(NAME)                TIME_FIELD_LAST(NAME)", "
    #define TIME_KEY_FIELD_LAST(KEY,NAME)   "s:(i,i,i,i)"
    #define TIME_KEY_FIELD(KEY,NAME)        TIME_KEY_FIELD_LAST(KEY,NAME)", "
    #undef FORMAT
#elif defined FIELDS
    #define SPA_FIELD_LAST(FIELD)           #FIELD, spa.FIELD
    #define SPA_FIELD(FIELD)                SPA_FIELD_LAST(FIELD),
    #define TIME_FIELD_LAST(NAME)           #NAME, NAME##_hour, NAME##_min, NAME##_sec, NAME##_microsec
    #define TIME_FIELD(NAME)                TIME_FIELD_LAST(NAME),
    #define TIME_KEY_FIELD_LAST(KEY,NAME)   #KEY, NAME##_hour, NAME##_min, NAME##_sec, NAME##_microsec
    #define TIME_KEY_FIELD(KEY,NAME)        TIME_KEY_FIELD_LAST(KEY,NAME),
    #undef FIELDS
#else
    #error neither FORMAT nor FIELDS usage macros are defined
#endif

SPA_FIELD(jd)               // Julian day
SPA_FIELD(jc)               // Julian century
SPA_FIELD(jde)              // Julian ephemeris day
SPA_FIELD(jce)              // Julian ephemeris century
SPA_FIELD(jme)              // Julian ephemeris millennium
SPA_FIELD(l)                // earth heliocentric longitude [degrees]
SPA_FIELD(b)                // earth heliocentric latitude [degrees]
SPA_FIELD(r)                // earth radius vector [Astronomical Units)  AU]
SPA_FIELD(theta)            // geocentric longitude [degrees]
SPA_FIELD(beta)             // geocentric latitude [degrees]
SPA_FIELD(x0)               // mean elongation (moon-sun) [degrees]
SPA_FIELD(x1)               // mean anomaly (sun) [degrees]
SPA_FIELD(x2)               // mean anomaly (moon) [degrees]
SPA_FIELD(x3)               // argument latitude (moon) [degrees]
SPA_FIELD(x4)               // ascending longitude (moon) [degrees]
SPA_FIELD(del_psi)          // nutation longitude [degrees]
SPA_FIELD(del_epsilon)      // nutation obliquity [degrees]
SPA_FIELD(epsilon0)         // ecliptic mean obliquity [arc seconds]
SPA_FIELD(epsilon)          // ecliptic true obliquity  [degrees]
SPA_FIELD(del_tau)          // aberration correction [degrees]
SPA_FIELD(lamda)            // apparent sun longitude [degrees]
SPA_FIELD(nu0)              // Greenwich mean sidereal time [degrees]
SPA_FIELD(nu)               // Greenwich sidereal time [degrees]
SPA_FIELD(alpha)            // geocentric sun right ascension [degrees]
SPA_FIELD(delta)            // geocentric sun declination [degrees]
SPA_FIELD(h)                // observer hour angle [degrees]
SPA_FIELD(xi)               // sun equatorial horizontal parallax [degrees]
SPA_FIELD(del_alpha)        // sun right ascension parallax [degrees]
SPA_FIELD(delta_prime)      // topocentric sun declination [degrees]
SPA_FIELD(alpha_prime)      // topocentric sun right ascension [degrees]
SPA_FIELD(h_prime)          // topocentric local hour angle [degrees])
SPA_FIELD(h0_prime)
SPA_FIELD(delta_zero)
SPA_FIELD(e0)               // topocentric elevation angle (uncorrected) [degrees]
SPA_FIELD(del_e)            // atmospheric refraction correction [degrees]
SPA_FIELD(e)                // topocentric elevation angle (corrected) [degrees]
SPA_FIELD(eot)              // equation of time [minutes]
SPA_FIELD(srha)             // sunrise hour angle [degrees]
SPA_FIELD(ssha)             // sunset hour angle [degrees]
SPA_FIELD(sta)              // sun transit altitude [degrees]
SPA_FIELD(zenith)           // topocentric zenith angle [degrees]
SPA_FIELD(azimuth180)       // topocentric azimuth angle (westward from south) [-180 to 180 degrees]
SPA_FIELD(azimuth)          // topocentric azimuth angle (eastward from north) [   0 to 360 degrees]
SPA_FIELD(incidence)        // surface incidence angle [degrees]
SPA_FIELD(suntransit)       // local sun transit time (or solar noon) [fractional hour]
SPA_FIELD(sunrise)          // local sunrise time (+/- 30 seconds) [fractional hour]
SPA_FIELD(sunset)           // local sunset time (+/- 30 seconds) [fractional hour]
TIME_FIELD(sunrise)
TIME_FIELD(sunset)
TIME_KEY_FIELD_LAST(noon, transit)  // must use a xxx_LAST macro on last one

// clean up to prevent warnings about redefining macros
#undef SPA_FIELD_LAST
#undef SPA_FIELD
#undef TIME_FIELD_LAST
#undef TIME_FIELD
#undef TIME_KEY_FIELD_LAST
#undef TIME_KEY_FIELD

一旦您完成所有设置，您的 build_dict() 函数就会变得相当短并且独立于字典的实际内容：

// build format string using header
char format_string[] = "{"
    #define FORMAT
    #include "builddict.h"
"}";

// use header again to build list of fields
PyObject* build_dict(SPA spa)
{
    return Py_BuildValue(format_string,
        #define FIELDS
        #include "builddict.h"
    );
}

虽然这并不能完全自动化该过程，但可以有很多帮助。可能有其他可用的文本处理或 C 接口工具（或者您可以编写自己的工具）来进一步帮助您创建此单个头文件，因为它采用非常统一的格式。

Answer 2

鉴于大多数值似乎来自 spa，将其与其他松散属性一起封装可能是更好的主意 在一个对象内并返回它。另外，datetime.time。

Answer 3

您可以使用宏：

#define ADD_FIELD(F) PyDict_SetItemString(d, #F, spa.F)
ADD_FIELD(jd);
ADD_FIELD(jc);
...

这将防止字符串名称和格式字符串出现错误。
未列出所有字段的错误不容易防止 AFAICT。

另外，您可以删除尾随的 \0；它没有任何目的。

Answer 4

如果多个结构需要这样做，那么我可能会编写一个小的 python 脚本，通过从 .h 读取结构定义来生成此代码（例如，通过用特殊注释标记需要导出为字典的结构和字段是什么） ）...所示情况下的最后三个字段需要手动添加到字典中。

我不会只对一个结构这样做，特别是如果该结构是稳定的。

您是否考虑过使用 SIP 等导出对象而不是字典？