+In some cases, users may wish to instead handle all byte strings as bytes +objects in Python 3. This can be accomplished by adding +SWIG_PYTHON_STRICT_BYTE_CHAR to the generated code: +
+ +
+%module char_to_bytes
+%begin %{
+#define SWIG_PYTHON_STRICT_BYTE_CHAR
+%}
+
+char *charstring(char *s) {
+ return s;
+}
++This will modify the behavior so that only Python 3 bytes objects will be +accepted and converted to a C/C++ string, and any string returned from C/C++ +will be converted to a bytes object in Python 3: +
+ +
+>>> from char_to_bytes import *
+>>> charstring(b"hi") # Byte string
+b'hi'
+>>> charstring("hi") # Unicode string
+Traceback (most recent call last):
+ File "<stdin>", line 1, in ?
+TypeError: in method 'charstring', argument 1 of type 'char *'
++Note that in Python 2, defining SWIG_PYTHON_STRICT_BYTE_CHAR has no +effect, since strings in Python 2 are equivalent to Python 3 bytes objects. +However, there is a similar capability to force unicode-only handling for +wide characters C/C++ strings (wchar_t * or std::wstring +types) in Python 2. By default, in Python 2 both strings and unicode strings +are converted to C/C++ wide strings, and returned wide strings are converted +to a Python unicode string. To instead only convert unicode strings to wide +strings, users can add SWIG_PYTHON_STRICT_UNICODE_WCHAR to the +generated code: +
+ +
+%module wchar_to_unicode
+%begin %{
+#define SWIG_PYTHON_STRICT_UNICODE_WCHAR
+%}
+
+wchar_t *wcharstring(wchar_t *s) {
+ return s;
+}
++This ensures that only unicode strings are accepted by wcharstring in both +Python 2 and Python 3: +
+ ++>>> from wchar_to_unicode import * +>>> wcharstring(u"hi") # Unicode string +u'hi' +>>> wcharstring(b"hi") # Byte string +Traceback (most recent call last): + File "<stdin>", line 1, in ? +TypeError: in method 'charstring', argument 1 of type 'wchar_t *' +
+By defining both SWIG_PYTHON_STRICT_BYTE_CHAR and +SWIG_PYTHON_STRICT_UNICODE_WCHAR, Python wrapper code can support +overloads taking both std::string (as Python bytes) and std::wstring +(as Python unicode). +
++Note that defining both SWIG_PYTHON_2_UNICODE and +SWIG_PYTHON_STRICT_BYTE_CHAR at the same time is not allowed, since +the first is allowing unicode conversion and the second is explicitly +prohibiting it. +
+