gh-121249: make complex types available unconditionally in the struct module

Each complex type interpreted as an array type containing exactly two
elements of the corresponding real type (real and imaginary parts,
respectively).

Author: skirpichev

Doc/library/struct.rst

@@ -260,24 +260,17 @@ platform-dependent.
 +--------+--------------------------+--------------------+----------------+------------+
 | ``d``  | :c:expr:`double`         | float              | 8              | \(4)       |
 +--------+--------------------------+--------------------+----------------+------------+
+| ``F``  | :c:expr:`float complex`  | complex            | 8              | \(10)      |
++--------+--------------------------+--------------------+----------------+------------+
+| ``D``  | :c:expr:`double complex` | complex            | 16             | \(10)      |
++--------+--------------------------+--------------------+----------------+------------+
 | ``s``  | :c:expr:`char[]`         | bytes              |                | \(9)       |
 +--------+--------------------------+--------------------+----------------+------------+
 | ``p``  | :c:expr:`char[]`         | bytes              |                | \(8)       |
 +--------+--------------------------+--------------------+----------------+------------+
 | ``P``  | :c:expr:`void \*`        | integer            |                | \(5)       |
 +--------+--------------------------+--------------------+----------------+------------+
 
-Additionally, if IEC 60559 compatible complex arithmetic (Annex G of the
-C11 standard) is supported, the following format characters are available:
-
-+--------+--------------------------+--------------------+----------------+------------+
-| Format | C Type                   | Python type        | Standard size  | Notes      |
-+========+==========================+====================+================+============+
-| ``F``  | :c:expr:`float complex`  | complex            | 8              | \(10)      |
-+--------+--------------------------+--------------------+----------------+------------+
-| ``D``  | :c:expr:`double complex` | complex            | 16             | \(10)      |
-+--------+--------------------------+--------------------+----------------+------------+
-
 .. versionchanged:: 3.3
    Added support for the ``'n'`` and ``'N'`` formats.
 
@@ -367,6 +360,12 @@ Notes:
    For the ``'E'`` and ``'C'`` format characters, the packed representation uses
    the IEEE 754 binary32 and binary64 format for components of the complex
    number, regardless of the floating-point format used by the platform.
+   Note that support for complex types is available unconditionally,
+   regardless on support IEC 60559 compatible complex arithmetic (Annex G of
+   the C11 standard) by the compiler.  Each complex type is interpreted as an
+   array type containing exactly two elements of the corresponding real type
+   (real and imaginary parts, respectively).
+
 
 A format character may be preceded by an integral repeat count.  For example,
 the format string ``'4h'`` means exactly the same as ``'hhhh'``.

Doc/whatsnew/3.14.rst

@@ -1309,8 +1309,8 @@ struct
 ------
 
 * Support the :c:expr:`float complex` and :c:expr:`double complex` C types in
-  the :mod:`struct` module (formatting characters ``'F'`` and ``'D'``,
-  respectively) if the compiler has C11 complex arithmetic.
+  the :mod:`struct` module (formatting characters ``'F'`` and ``'D'``
+  respectively).
   (Contributed by Sergey B Kirpichev in :gh:`121249`.)
 
 

Lib/test/test_struct.py

@@ -22,12 +22,6 @@
 INF = float('inf')
 NAN = float('nan')
 
-try:
-    struct.pack('D', 1j)
-    have_c_complex = True
-except struct.error:
-    have_c_complex = False
-
 def iter_integer_formats(byteorders=byteorders):
     for code in integer_codes:
         for byteorder in byteorders:
@@ -796,7 +790,6 @@ def test_repr(self):
         s = struct.Struct('=i2H')
         self.assertEqual(repr(s), f'Struct({s.format!r})')
 
-    @unittest.skipUnless(have_c_complex, "requires C11 complex type support")
     def test_c_complex_round_trip(self):
         values = [complex(*_) for _ in combinations([1, -1, 0.0, -0.0, 2,
                                                      -3, INF, -INF, NAN], 2)]
@@ -806,19 +799,6 @@ def test_c_complex_round_trip(self):
                     round_trip = struct.unpack(f, struct.pack(f, z))[0]
                     self.assertComplexesAreIdentical(z, round_trip)
 
-    @unittest.skipIf(have_c_complex, "requires no C11 complex type support")
-    def test_c_complex_error(self):
-        msg1 = "'F' format not supported on this system"
-        msg2 = "'D' format not supported on this system"
-        with self.assertRaisesRegex(struct.error, msg1):
-            struct.pack('F', 1j)
-        with self.assertRaisesRegex(struct.error, msg1):
-            struct.unpack('F', b'1')
-        with self.assertRaisesRegex(struct.error, msg2):
-            struct.pack('D', 1j)
-        with self.assertRaisesRegex(struct.error, msg2):
-            struct.unpack('D', b'1')
-
 
 class UnpackIteratorTest(unittest.TestCase):
     """

Misc/NEWS.d/next/Library/2025-04-25-16-20-49.gh-issue-121249.uue2nK.rst

@@ -0,0 +1,2 @@
+Support the :c:expr:`float complex` and :c:expr:`double complex` C types in
+the :mod:`struct` module.  Patch by Sergey B Kirpichev.

Modules/_struct.c

@@ -12,9 +12,6 @@
 #include "pycore_long.h"          // _PyLong_AsByteArray()
 #include "pycore_moduleobject.h"  // _PyModule_GetState()
 
-#ifdef Py_HAVE_C_COMPLEX
-#  include "_complex.h"           // complex
-#endif
 #include <stddef.h>               // offsetof()
 
 /*[clinic input]
@@ -495,25 +492,23 @@ nu_double(_structmodulestate *state, const char *p, const formatdef *f)
     return PyFloat_FromDouble(x);
 }
 
-#ifdef Py_HAVE_C_COMPLEX
 static PyObject *
 nu_float_complex(_structmodulestate *state, const char *p, const formatdef *f)
 {
-    float complex x;
+    float x[2];
 
     memcpy(&x, p, sizeof(x));
-    return PyComplex_FromDoubles(creal(x), cimag(x));
+    return PyComplex_FromDoubles(x[0], x[1]);
 }
 
 static PyObject *
 nu_double_complex(_structmodulestate *state, const char *p, const formatdef *f)
 {
-    double complex x;
+    double x[2];
 
     memcpy(&x, p, sizeof(x));
-    return PyComplex_FromDoubles(creal(x), cimag(x));
+    return PyComplex_FromDoubles(x[0], x[1]);
 }
-#endif
 
 static PyObject *
 nu_void_p(_structmodulestate *state, const char *p, const formatdef *f)
@@ -788,13 +783,12 @@ np_double(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
     return 0;
 }
 
-#ifdef Py_HAVE_C_COMPLEX
 static int
 np_float_complex(_structmodulestate *state, char *p, PyObject *v,
                  const formatdef *f)
 {
     Py_complex c = PyComplex_AsCComplex(v);
-    float complex x = CMPLXF((float)c.real, (float)c.imag);
+    float x[2] = {(float)c.real, (float)c.imag};
 
     if (c.real == -1 && PyErr_Occurred()) {
         PyErr_SetString(state->StructError,
@@ -810,7 +804,7 @@ np_double_complex(_structmodulestate *state, char *p, PyObject *v,
                   const formatdef *f)
 {
     Py_complex c = PyComplex_AsCComplex(v);
-    double complex x = CMPLX(c.real, c.imag);
+    double x[2] = {c.real, c.imag};
 
     if (c.real == -1 && PyErr_Occurred()) {
         PyErr_SetString(state->StructError,
@@ -820,25 +814,6 @@ np_double_complex(_structmodulestate *state, char *p, PyObject *v,
     memcpy(p, &x, sizeof(x));
     return 0;
 }
-#else
-static int
-np_complex_stub(_structmodulestate *state, char *p, PyObject *v,
-                const formatdef *f)
-{
-    PyErr_Format(state->StructError,
-                 "'%c' format not supported on this system",
-                 f->format);
-    return -1;
-}
-static PyObject *
-nu_complex_stub(_structmodulestate *state, const char *p, const formatdef *f)
-{
-    PyErr_Format(state->StructError,
-                 "'%c' format not supported on this system",
-                 f->format);
-    return NULL;
-}
-#endif
 
 static int
 np_void_p(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
@@ -878,13 +853,8 @@ static const formatdef native_table[] = {
     {'e',       sizeof(short),  _Alignof(short),    nu_halffloat,   np_halffloat},
     {'f',       sizeof(float),  _Alignof(float),    nu_float,       np_float},
     {'d',       sizeof(double), _Alignof(double),   nu_double,      np_double},
-#ifdef Py_HAVE_C_COMPLEX
-    {'F',       sizeof(float complex), _Alignof(float complex), nu_float_complex, np_float_complex},
-    {'D',       sizeof(double complex), _Alignof(double complex), nu_double_complex, np_double_complex},
-#else
-    {'F',       1, 0, nu_complex_stub, np_complex_stub},
-    {'D',       1, 0, nu_complex_stub, np_complex_stub},
-#endif
+    {'F',       2*sizeof(float), _Alignof(float[2]), nu_float_complex, np_float_complex},
+    {'D',       2*sizeof(double), _Alignof(double[2]), nu_double_complex, np_double_complex},
     {'P',       sizeof(void *), _Alignof(void *),   nu_void_p,      np_void_p},
     {0}
 };
@@ -985,7 +955,6 @@ bu_double(_structmodulestate *state, const char *p, const formatdef *f)
     return unpack_double(p, 0);
 }
 
-#ifdef Py_HAVE_C_COMPLEX
 static PyObject *
 bu_float_complex(_structmodulestate *state, const char *p, const formatdef *f)
 {
@@ -1015,7 +984,6 @@ bu_double_complex(_structmodulestate *state, const char *p, const formatdef *f)
     }
     return PyComplex_FromDoubles(x, y);
 }
-#endif
 
 static PyObject *
 bu_bool(_structmodulestate *state, const char *p, const formatdef *f)
@@ -1156,7 +1124,6 @@ bp_double(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
     return PyFloat_Pack8(x, p, 0);
 }
 
-#ifdef Py_HAVE_C_COMPLEX
 static int
 bp_float_complex(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
 {
@@ -1186,7 +1153,6 @@ bp_double_complex(_structmodulestate *state, char *p, PyObject *v, const formatd
     }
     return PyFloat_Pack8(x.imag, p + 8, 0);
 }
-#endif
 
 static int
 bp_bool(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
@@ -1218,13 +1184,8 @@ static formatdef bigendian_table[] = {
     {'e',       2,              0,              bu_halffloat,   bp_halffloat},
     {'f',       4,              0,              bu_float,       bp_float},
     {'d',       8,              0,              bu_double,      bp_double},
-#ifdef Py_HAVE_C_COMPLEX
     {'F',       8,              0,              bu_float_complex, bp_float_complex},
     {'D',       16,             0,              bu_double_complex, bp_double_complex},
-#else
-    {'F',       1,              0,              nu_complex_stub, np_complex_stub},
-    {'D',       1,              0,              nu_complex_stub, np_complex_stub},
-#endif
     {0}
 };
 
@@ -1324,7 +1285,6 @@ lu_double(_structmodulestate *state, const char *p, const formatdef *f)
     return unpack_double(p, 1);
 }
 
-#ifdef Py_HAVE_C_COMPLEX
 static PyObject *
 lu_float_complex(_structmodulestate *state, const char *p, const formatdef *f)
 {
@@ -1354,7 +1314,6 @@ lu_double_complex(_structmodulestate *state, const char *p, const formatdef *f)
     }
     return PyComplex_FromDoubles(x, y);
 }
-#endif
 
 static int
 lp_int(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
@@ -1489,7 +1448,6 @@ lp_double(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
     return PyFloat_Pack8(x, p, 1);
 }
 
-#ifdef Py_HAVE_C_COMPLEX
 static int
 lp_float_complex(_structmodulestate *state, char *p, PyObject *v, const formatdef *f)
 {
@@ -1520,7 +1478,6 @@ lp_double_complex(_structmodulestate *state, char *p, PyObject *v, const formatd
     }
     return PyFloat_Pack8(x.imag, p + 8, 1);
 }
-#endif
 
 static formatdef lilendian_table[] = {
     {'x',       1,              0,              NULL},
@@ -1542,13 +1499,8 @@ static formatdef lilendian_table[] = {
     {'e',       2,              0,              lu_halffloat,   lp_halffloat},
     {'f',       4,              0,              lu_float,       lp_float},
     {'d',       8,              0,              lu_double,      lp_double},
-#ifdef Py_HAVE_C_COMPLEX
     {'F',       8,              0,              lu_float_complex, lp_float_complex},
     {'D',       16,             0,              lu_double_complex, lp_double_complex},
-#else
-    {'F',       1,              0,              nu_complex_stub, np_complex_stub},
-    {'D',       1,              0,              nu_complex_stub, np_complex_stub},
-#endif
     {0}
 };