davebshow · March 25, 2018 16:25 · Mar 25, 2018
diff --git a/transformer.py b/transformer.py
@@ -0,0 +1,61 @@
+import functools
+
+import pandas as pd
+
+
+class Transformer:
+
+    __mappings__ = {}
+
+    @classmethod
+    def transform(cls, df, *, groupby=None, filter=None):
+        transformer = cls(df, groupby=groupby, filter=filter)
+        return transformer.apply_mappings()
+
+    @classmethod
+    def mapping(cls, target_key):
+        if not isinstance(target_key, str):
+            raise RuntimeError("`mapping` decorator requires pos arg `target key`")
+
+        def _mapping(fn):
+
+            cls.__mappings__[target_key] = fn
+
+            @functools.wraps(fn)
+            def wrapper(*args, **kwargs):
+                return fn(*args, **kwargs)
+
+            return wrapper
+
+        return _mapping
+
+    def __init__(self, df):
+        self._df = df
+
+    def _call(self, name):
+        return self.__mappings__[name](self._df)
+
+    def apply_mappings(self):
+        return NotImplementedError
+
+
+class PandasTransformer(Transformer):
+
+    def __init__(self, df, *, groupby=None, filter=None):
+        if filter:
+            df = df[df[filter]]
+        if groupby:
+            df = df.groupby(groupby)
+        self._output_df = pd.DataFrame(columns=self.__mappings__.keys())
+        super().__init__(df)
+
+    def apply_mappings(self):
+        for key, value in self.__mappings__.items():
+            self._output_df.loc[:, key] = value(self._df)
+        return self._output_df
+
+
+
+@Transformer.mapping('target')
+def add(a, b):
+    return a + b