# Buggy code
def generate_module_preamble(self, env, options, cimported_modules, metadata, code):
    code.put_generated_by()
    if metadata:
        code.putln("/* BEGIN: Cython Metadata")
        code.putln(json.dumps(metadata, indent=4, sort_keys=True))
        code.putln("END: Cython Metadata */")
        code.putln("")
    code.putln("#define PY_SSIZE_T_CLEAN")

    for inc in sorted(env.c_includes.values(), key=IncludeCode.sortkey):
        if inc.location == inc.INITIAL:
            inc.write(code)
    code.putln("#ifndef Py_PYTHON_H")
    code.putln(
        "    #error Python headers needed to compile C extensions, "
        "please install development version of Python."
    )
    code.putln(
        "#elif PY_VERSION_HEX < 0x02070000 || "
        "(0x03000000 <= PY_VERSION_HEX && PY_VERSION_HEX < 0x03030000)"
    )
    code.putln("    #error Cython requires Python 2.7+ or Python 3.3+.")
    code.putln("#else")
    code.globalstate["end"].putln("#endif /* Py_PYTHON_H */")

    from .. import __version__

    code.putln('#define CYTHON_ABI "%s"' % __version__.replace(".", "_"))
    code.putln("#define CYTHON_HEX_VERSION %s" % build_hex_version(__version__))
    code.putln(
        "#define CYTHON_FUTURE_DIVISION %d"
        % (Future.division in env.context.future_directives)
    )

    self._put_setup_code(code, "CModulePreamble")
    if env.context.options.cplus:
        self._put_setup_code(code, "CppInitCode")
    else:
        self._put_setup_code(code, "CInitCode")
    self._put_setup_code(code, "PythonCompatibility")
    self._put_setup_code(code, "MathInitCode")

    if options.c_line_in_traceback:
        cinfo = "%s = %s; " % (Naming.clineno_cname, Naming.line_c_macro)
    else:
        cinfo = ""
    code.put(
        """
#define __PYX_ERR(f_index, lineno, Ln_error) \\
{ \\
  %s = %s[f_index]; %s = lineno; %sgoto Ln_error; \\
}
"""
        % (Naming.filename_cname, Naming.filetable_cname, Naming.lineno_cname, cinfo)
    )

    code.putln("")
    self.generate_extern_c_macro_definition(code)
    code.putln("")

    code.putln("#define %s" % Naming.h_guard_prefix + self.api_name(env))
    code.putln("#define %s" % Naming.api_guard_prefix + self.api_name(env))
    code.putln("/* Early includes */")
    self.generate_includes(env, cimported_modules, code, late=False)
    code.putln("")
    code.putln(
        "#if defined(PYREX_WITHOUT_ASSERTIONS) && !defined(CYTHON_WITHOUT_ASSERTIONS)"
    )
    code.putln("#define CYTHON_WITHOUT_ASSERTIONS")
    code.putln("#endif")
    code.putln("")

    if env.directives["ccomplex"]:
        code.putln("")
        code.putln("#if !defined(CYTHON_CCOMPLEX)")
        code.putln("#define CYTHON_CCOMPLEX 1")
        code.putln("#endif")
        code.putln("")
    code.put(
        UtilityCode.load_as_string(
            "UtilityFunctionPredeclarations", "ModuleSetupCode.c"
        )[0]
    )

    c_string_type = env.directives["c_string_type"]
    c_string_encoding = env.directives["c_string_encoding"]
    if c_string_type not in ("bytes", "bytearray") and not c_string_encoding:
        error(
            self.pos,
            "a default encoding must be provided if c_string_type is not a byte type",
        )
    code.putln(
        "#define __PYX_DEFAULT_STRING_ENCODING_IS_ASCII %s"
        % int(c_string_encoding == "ascii")
    )
    if c_string_encoding == "default":
        code.putln("#define __PYX_DEFAULT_STRING_ENCODING_IS_DEFAULT 1")
    else:
        code.putln("#define __PYX_DEFAULT_STRING_ENCODING_IS_DEFAULT 0")
        code.putln('#define __PYX_DEFAULT_STRING_ENCODING "%s"' % c_string_encoding)
    if c_string_type == "bytearray":
        c_string_func_name = "ByteArray"
    else:
        c_string_func_name = c_string_type.title()
    code.putln(
        "#define __Pyx_PyObject_FromString __Pyx_Py%s_FromString" % c_string_func_name
    )
    code.putln(
        "#define __Pyx_PyObject_FromStringAndSize __Pyx_Py%s_FromStringAndSize"
        % c_string_func_name
    )
    code.put(UtilityCode.load_as_string("TypeConversions", "TypeConversion.c")[0])

    # These utility functions are assumed to exist and used elsewhere.
    PyrexTypes.c_long_type.create_to_py_utility_code(env)
    PyrexTypes.c_long_type.create_from_py_utility_code(env)
    PyrexTypes.c_int_type.create_from_py_utility_code(env)

    code.put(Nodes.branch_prediction_macros)
    code.putln(
        "static CYTHON_INLINE void __Pyx_pretend_to_initialize(void* ptr) { (void)ptr; }"
    )
    code.putln("")
    code.putln("static PyObject *%s = NULL;" % env.module_cname)
    code.putln("static PyObject *%s;" % env.module_dict_cname)
    code.putln("static PyObject *%s;" % Naming.builtins_cname)
    code.putln("static PyObject *%s = NULL;" % Naming.cython_runtime_cname)
    code.putln("static PyObject *%s;" % Naming.empty_tuple)
    code.putln("static PyObject *%s;" % Naming.empty_bytes)
    code.putln("static PyObject *%s;" % Naming.empty_unicode)
    if Options.pre_import is not None:
        code.putln("static PyObject *%s;" % Naming.preimport_cname)
    code.putln("static int %s;" % Naming.lineno_cname)
    code.putln("static int %s = 0;" % Naming.clineno_cname)
    code.putln(
        "static const char * %s= %s;" % (Naming.cfilenm_cname, Naming.file_c_macro)
    )
    code.putln("static const char *%s;" % Naming.filename_cname)

    env.use_utility_code(UtilityCode.load_cached("FastTypeChecks", "ModuleSetupCode.c"))
    if has_np_pythran(env):
        env.use_utility_code(
            UtilityCode.load_cached("PythranConversion", "CppSupport.cpp")
        )


# Traceback (TypeError)
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "test.pyx", line 6, in test.test
File "stringsource", line 15, in string.from_py.__pyx_convert_string_from_py_std__in_string
TypeError: expected bytes, str found

# Fixed code
def generate_module_preamble(self, env, options, cimported_modules, metadata, code):
    code.put_generated_by()
    if metadata:
        code.putln("/* BEGIN: Cython Metadata")
        code.putln(json.dumps(metadata, indent=4, sort_keys=True))
        code.putln("END: Cython Metadata */")
        code.putln("")
    code.putln("#define PY_SSIZE_T_CLEAN")

    for inc in sorted(env.c_includes.values(), key=IncludeCode.sortkey):
        if inc.location == inc.INITIAL:
            inc.write(code)
    code.putln("#ifndef Py_PYTHON_H")
    code.putln(
        "    #error Python headers needed to compile C extensions, "
        "please install development version of Python."
    )
    code.putln(
        "#elif PY_VERSION_HEX < 0x02070000 || "
        "(0x03000000 <= PY_VERSION_HEX && PY_VERSION_HEX < 0x03030000)"
    )
    code.putln("    #error Cython requires Python 2.7+ or Python 3.3+.")
    code.putln("#else")
    code.globalstate["end"].putln("#endif /* Py_PYTHON_H */")

    from .. import __version__

    code.putln('#define CYTHON_ABI "%s"' % __version__.replace(".", "_"))
    code.putln("#define CYTHON_HEX_VERSION %s" % build_hex_version(__version__))
    code.putln(
        "#define CYTHON_FUTURE_DIVISION %d"
        % (Future.division in env.context.future_directives)
    )

    self._put_setup_code(code, "CModulePreamble")
    if env.context.options.cplus:
        self._put_setup_code(code, "CppInitCode")
    else:
        self._put_setup_code(code, "CInitCode")
    self._put_setup_code(code, "PythonCompatibility")
    self._put_setup_code(code, "MathInitCode")

    if options.c_line_in_traceback:
        cinfo = "%s = %s; " % (Naming.clineno_cname, Naming.line_c_macro)
    else:
        cinfo = ""
    code.put(
        """
#define __PYX_ERR(f_index, lineno, Ln_error) \\
{ \\
  %s = %s[f_index]; %s = lineno; %sgoto Ln_error; \\
}
"""
        % (Naming.filename_cname, Naming.filetable_cname, Naming.lineno_cname, cinfo)
    )

    code.putln("")
    self.generate_extern_c_macro_definition(code)
    code.putln("")

    code.putln("#define %s" % Naming.h_guard_prefix + self.api_name(env))
    code.putln("#define %s" % Naming.api_guard_prefix + self.api_name(env))
    code.putln("/* Early includes */")
    self.generate_includes(env, cimported_modules, code, late=False)
    code.putln("")
    code.putln(
        "#if defined(PYREX_WITHOUT_ASSERTIONS) && !defined(CYTHON_WITHOUT_ASSERTIONS)"
    )
    code.putln("#define CYTHON_WITHOUT_ASSERTIONS")
    code.putln("#endif")
    code.putln("")

    if env.directives["ccomplex"]:
        code.putln("")
        code.putln("#if !defined(CYTHON_CCOMPLEX)")
        code.putln("#define CYTHON_CCOMPLEX 1")
        code.putln("#endif")
        code.putln("")
    code.put(
        UtilityCode.load_as_string(
            "UtilityFunctionPredeclarations", "ModuleSetupCode.c"
        )[0]
    )

    c_string_type = env.directives["c_string_type"]
    c_string_encoding = env.directives["c_string_encoding"]
    if c_string_type not in ("bytes", "bytearray") and not c_string_encoding:
        error(
            self.pos,
            "a default encoding must be provided if c_string_type is not a byte type",
        )
    code.putln(
        "#define __PYX_DEFAULT_STRING_ENCODING_IS_ASCII %s"
        % int(c_string_encoding == "ascii")
    )
    code.putln(
        "#define __PYX_DEFAULT_STRING_ENCODING_IS_UTF8 %s"
        % int(c_string_encoding.replace("-", "").lower() == "utf8")
    )
    if c_string_encoding == "default":
        code.putln("#define __PYX_DEFAULT_STRING_ENCODING_IS_DEFAULT 1")
    else:
        code.putln(
            "#define __PYX_DEFAULT_STRING_ENCODING_IS_DEFAULT "
            "(PY_MAJOR_VERSION >= 3 && __PYX_DEFAULT_STRING_ENCODING_IS_UTF8)"
        )
        code.putln('#define __PYX_DEFAULT_STRING_ENCODING "%s"' % c_string_encoding)
    if c_string_type == "bytearray":
        c_string_func_name = "ByteArray"
    else:
        c_string_func_name = c_string_type.title()
    code.putln(
        "#define __Pyx_PyObject_FromString __Pyx_Py%s_FromString" % c_string_func_name
    )
    code.putln(
        "#define __Pyx_PyObject_FromStringAndSize __Pyx_Py%s_FromStringAndSize"
        % c_string_func_name
    )
    code.put(UtilityCode.load_as_string("TypeConversions", "TypeConversion.c")[0])

    # These utility functions are assumed to exist and used elsewhere.
    PyrexTypes.c_long_type.create_to_py_utility_code(env)
    PyrexTypes.c_long_type.create_from_py_utility_code(env)
    PyrexTypes.c_int_type.create_from_py_utility_code(env)

    code.put(Nodes.branch_prediction_macros)
    code.putln(
        "static CYTHON_INLINE void __Pyx_pretend_to_initialize(void* ptr) { (void)ptr; }"
    )
    code.putln("")
    code.putln("static PyObject *%s = NULL;" % env.module_cname)
    code.putln("static PyObject *%s;" % env.module_dict_cname)
    code.putln("static PyObject *%s;" % Naming.builtins_cname)
    code.putln("static PyObject *%s = NULL;" % Naming.cython_runtime_cname)
    code.putln("static PyObject *%s;" % Naming.empty_tuple)
    code.putln("static PyObject *%s;" % Naming.empty_bytes)
    code.putln("static PyObject *%s;" % Naming.empty_unicode)
    if Options.pre_import is not None:
        code.putln("static PyObject *%s;" % Naming.preimport_cname)
    code.putln("static int %s;" % Naming.lineno_cname)
    code.putln("static int %s = 0;" % Naming.clineno_cname)
    code.putln(
        "static const char * %s= %s;" % (Naming.cfilenm_cname, Naming.file_c_macro)
    )
    code.putln("static const char *%s;" % Naming.filename_cname)

    env.use_utility_code(UtilityCode.load_cached("FastTypeChecks", "ModuleSetupCode.c"))
    if has_np_pythran(env):
        env.use_utility_code(
            UtilityCode.load_cached("PythranConversion", "CppSupport.cpp")
        )