added the config system

app/config.yml

@@ -0,0 +1,11 @@
+app_name: OpenFDA
+secret_key: a passphrase for peppering
+base_dir: !PY base_dir
+app_dir: !PY app_dir
+data_dir: !PY data_dir
+log_dir: !PY log_dir
+fda_data_url: https://download.open.fda.gov/drug/ndc/drug-ndc-0001-of-0001.json.zip
+server: 
+    host: 0.0.0.0
+sqllite_db_name: drugs.db
+json_file_name: !PY json_file_name

app/utils/config.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python
+"""apps.utils.config: imports and finalize config.yml"""
+
+from pathlib import Path
+import glob
+import yaml
+import os
+
+class PyVar(yaml.YAMLObject):
+    """
+    a class to create a custom !PY tag in yaml
+    The !PY tag allows calling python code stored in a dictionary
+    """
+    # this is a PYYAML requirment and is case sensitive
+    yaml_tag = u'!PY'
+
+    def __init__(self):
+        """
+        starts with empty dictionary
+        """
+        self.py_dict = {}
+
+    def get(self,key):
+        """
+        retrieves a value from the dictionary
+        """
+        return self.py_dict[key]
+
+    def add(self,key,value):
+        """
+        adds a new key value pair to a dictionary
+        """
+        self.py_dict[key] = value
+
+
+# construct all they key value pairs that can be referenced by the yaml file
+# creating a function like this is required for yaml.SafeLoader.add_constructor
+def yaml_construct(loader,node):
+    c = PyVar()
+    ## start adding python variables here
+    c.add('base_dir',Path(__file__).resolve(strict=True).parent.parent.parent.absolute())
+    c.add('app_dir', c.get('base_dir') / 'app')
+    c.add('data_dir', c.get('app_dir') / 'data')
+    c.add('log_dir', c.get('app_dir') / 'log')
+    c.add('json_file_name',os.path.basename(max(glob.glob(str(c.get('data_dir')) + '/*.json'), key=os.path.getctime)))
+    return c.get(node.value)
+
+# Required for safe_load
+yaml.SafeLoader.add_constructor('!PY', yaml_construct)
+
+# config.yml location
+configyml_path = Path(__file__).resolve(strict=True).parent.parent.absolute() / "config.yml"
+
+# load config.yml
+config = yaml.safe_load(open(configyml_path))
+
+if __name__ == "__main__":
+    print(config)