enable python3.7 builds

.travis.yml

@@ -1,8 +1,13 @@
 language: python
+
 python:
   - "2.7"
   - "3.5"
   - "3.6"
+  - "3.7-dev"
+
+allow_failures:
+  - python: "3.7-dev"
 
 env:
   global:

pyo3cls/src/module.rs

@@ -56,6 +56,7 @@ pub fn py3_init(fnname: &syn::Ident, name: &String, doc: syn::Lit) -> Tokens {
             // so we'll do it here in the module initialization:
             MODULE_DEF.m_name = concat!(stringify!(#m_name), "\0").as_ptr() as *const _;
 
+            #[cfg(py_sys_config = "WITH_THREAD")]
             pyo3::ffi::PyEval_InitThreads();
 
             let _module = pyo3::ffi::PyModule_Create(&mut MODULE_DEF);

src/pythonrun.rs

@@ -39,14 +39,20 @@ pub fn prepare_freethreaded_python() {
         if ffi::Py_IsInitialized() != 0 {
             // If Python is already initialized, we expect Python threading to also be initialized,
             // as we can't make the existing Python main thread acquire the GIL.
+            #[cfg(py_sys_config = "WITH_THREAD")]
             assert_ne!(ffi::PyEval_ThreadsInitialized(), 0);
         } else {
+            // If Python isn't initialized yet, we expect that Python threading
+            // isn't initialized either.
+            #[cfg(py_sys_config = "WITH_THREAD")]
+            assert_eq!(ffi::PyEval_ThreadsInitialized(), 0);
             // Initialize Python.
             // We use Py_InitializeEx() with initsigs=0 to disable Python signal handling.
             // Signal handling depends on the notion of a 'main thread', which doesn't exist in this case.
             // Note that the 'main thread' notion in Python isn't documented properly;
             // and running Python without one is not officially supported.
             ffi::Py_InitializeEx(0);
+            #[cfg(py_sys_config = "WITH_THREAD")]
             ffi::PyEval_InitThreads();
             // PyEval_InitThreads() will acquire the GIL,
             // but we don't want to hold it at this point
@@ -61,6 +67,7 @@ pub fn prepare_freethreaded_python() {
     });
 }
 
+
 #[doc(hidden)]
 pub fn prepare_pyo3_library() {
     START_PYO3.call_once(|| unsafe {