Support extending Python API from other crates

- Allow subclassing for some Python classes
- Prevent unnecessary copying for transformers
- Add execute function for Transformer
- Rename PythonPattern to PythonTransformer

Cargo.toml

@@ -33,6 +33,8 @@ faster_alloc = ["tikv-jemallocator"]
 full_fn_cmp = []
 mathematica_api = ["wolfram-library-link"]
 python_api = ["pyo3", "bincode"]
+# do not create a Python module but allow other crates to do so
+python_no_module = ["python_api"]
 # build a module that is independent of the specific Python version
 python_abi3 = ["pyo3/abi3", "pyo3/abi3-py37"]
 

build.rs

@@ -7,5 +7,5 @@ fn main() {
     let git_desc = String::from_utf8(output.stdout).unwrap();
     println!("cargo:rustc-env=SYMBOLICA_VERSION={}", git_desc);
     println!("cargo:rerun-if-changed=.git/HEAD");
-    println!("cargo:rerun-if-changed=build.rs")
+    println!("cargo:rerun-if-changed=build.rs");
 }