ISSUE-223: Allow py/initialize! settings to be read from a python.edn file (#226)

* Allow "py/initialize!" settings to be read from a `python.edn` file

* add documentation

* add missing paren, make flycheck happy

Author: jjtolton

CHANGELOG.md

@@ -1,4 +1,7 @@
 # Time for a ChangeLog!
+## 2.021
+ * Add support for a `python.edn` file, see `libpython-clj2.python/initialize!` documentation
+
 ## 2.020
  * Better support for running with `-Dlibpython_clj.manual_gil=true` - `with-manual-gil`.  
    Addresses [issue 221](https://github.com/clj-python/libpython-clj/issues/221).

src/libpython_clj2/python.clj

@@ -34,7 +34,8 @@ user> (py/py. np linspace 2 3 :num 10)
             [libpython-clj2.python.windows :as win]
             [tech.v3.datatype.ffi :as dtype-ffi]
             [tech.v3.datatype.errors :as errors]
-            [clojure.tools.logging :as log])
+            [clojure.tools.logging :as log]
+            clojure.edn)
   (:import [java.util Map List]
            [clojure.lang IFn]))
 
@@ -47,6 +48,26 @@ user> (py/py. np linspace 2 3 :num 10)
     "Initialize the python library.  If library path is not provided, then the system
   attempts to execute a simple python program and have python return system info.
 
+  Note: all of the options passed to `initialize!` may now be provided in 
+  a root-level `python.edn` file.  Example:
+
+  ```
+  ;; python.edn
+  {:python-executable   \"/usr/bin/python3.7\"
+   :python-library-path \"/usr/lib/libpython3.7m.so\"
+   :python-home         \"/usr/lib/python3.7\"
+   :python-verbose      true}
+  ```
+  or, using a local virtual environment:
+  ```
+  ;; python.edn
+  {:python-executable   \"env/bin/python\"}
+  ```
+
+  The file MUST be named `python.edn` and be in the root of the classpath.
+  With a `python.edn` file in place, the `initialize!` function may be called
+  with no arguments and the options will be read from the file. If arguments are 
+  passed to `initialize!` then they will override the values in the file.
 
   Returns either `:ok` in which case the initialization completed successfully or
   `:already-initialized` in which case we detected that python has already been
@@ -72,8 +93,12 @@ user> (py/py. np linspace 2 3 :num 10)
              no-io-redirect?]
       :as options}]
   (if-not (and (py-ffi/library-loaded?)
-                 (= 1 (py-ffi/Py_IsInitialized)))
-    (let [info (py-info/detect-startup-info options)
+               (= 1 (py-ffi/Py_IsInitialized)))
+    (let [python-edn-opts (-> (try (slurp "python.edn")
+                                   (catch java.io.FileNotFoundException _ "{}"))
+                              clojure.edn/read-string)
+          options (merge python-edn-opts options)
+          info (py-info/detect-startup-info options)
           _ (log/infof "Startup info %s" info)
           _ (when-let [lib-path (:java-library-path-addendum
                                  options (:java-library-path-addendum info))]