如果sys.maxunicode的返回值是65535，说明python是用--e
在我的gentoo上实验结果如下：
Out[2]:
呵呵，是使用UCS-4表示unicode的，就算是很生僻很生僻的字也能处理哦
由于好奇，又看了看/usr/portage/dev-lang/python/py
相关的代码如下：
# super-secret switch. don't use this unless you know what you're
# doing. enabling UCS2 support will break your existing python
# modules
use ucs2 \
&& myconf="${myconf} --enable-unicode=ucs2" \
|| myconf="${myconf} --enable-unicode=ucs4"
是使用ucs2这个use flag来定义--enable-unicode的。当激活ucs2，就采用--en
那么如果是手工编译python，不给出--enable-unicode的话，py
$ tar jxf /usr/portage/distfiles/Python-2.3.4.tar.bz2
$ cd Python-2.3.4
$ ./configure --help | grep unicode -u1
--disable-ipv6 Disable ipv6 support
--enable-unicode[=ucs[24]]
Enable Unicode strings (default is yes)
默认的--enable-unicode的参数是yes。那么到底是ucs2还是uc
echo "$as_me:$LINENO: checking what type to use for unicode" >&5
echo $ECHO_N "checking what type to use for unicode... $ECHO_C" >&6
# Check whether --enable-unicode or --disable-unicode was given.
if test "${enable_unicode+set}" = set; then
enableval="$enable_unicode"
else
enable_unicode=yes
fi;
if test $enable_unicode = yes
then
# Without any arguments, Py_UNICODE defaults to two-byte mode
case "$have_ucs4_tcl" in
yes) enable_unicode="ucs4"
;;
*) enable_unicode="ucs2"
;;
esac
fi
case "$enable_unicode" in
ucs2) unicode_size="2"
cat >>confdefs.h <<\_ACEOF
#define Py_UNICODE_SIZE 2
_ACEOF
;;
ucs4) unicode_size="4"
cat >>confdefs.h <<\_ACEOF
#define Py_UNICODE_SIZE 4
_ACEOF
;;
esac
可以看出，当--enable-unicode=yes时，configure是根据$h
echo "$as_me:$LINENO: checking for UCS-4 tcl" >&5
echo $ECHO_N "checking for UCS-4 tcl... $ECHO_C" >&6
have_ucs4_tcl=no
cat >conftest.$ac_ext <<_ACEOF
#line $LINENO "configure"
/* confdefs.h. */
_ACEOF
cat confdefs.h >>conftest.$ac_ext
cat >>conftest.$ac_ext <<_ACEOF
/* end confdefs.h. */
#include <tcl.h>
#if TCL_UTF_MAX != 6
# error "NOT UCS4_TCL"
#endif
int
main ()
{
;
return 0;
}
_ACEOF
rm -f conftest.$ac_objext
if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
(eval $ac_compile) 2>&5
ac_status=$?
echo "$as_me:$LINENO: \$? = $ac_status" >&5
(exit $ac_status); } &&
{ ac_try='test -s conftest.$ac_objext'
{ (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
(eval $ac_try) 2>&5
ac_status=$?
echo "$as_me:$LINENO: \$? = $ac_status" >&5
(exit $ac_status); }; }; then
cat >>confdefs.h <<\_ACEOF
#define HAVE_UCS4_TCL 1
_ACEOF
have_ucs4_tcl=yes
else
echo "$as_me: failed program was:" >&5
sed 's/^/| /' conftest.$ac_ext >&5
fi
rm -f conftest.$ac_objext conftest.$ac_ext
echo "$as_me:$LINENO: result: $have_ucs4_tcl" >&5
echo "${ECHO_T}$have_ucs4_tcl" >&6
原来是根据tcl.h中TCL_UTF_MAX宏是否为6来判断的，如果为6，则使用
