Making a store out of a (data fetching) function list.

Relevant to #54.

py2store/sources.py

@@ -0,0 +1,42 @@
+# from py2store.util import lazyprop, num_of_args
+from py2store.base import KvReader
+
+
+class FuncReader(KvReader):
+    """Reader that seeds itself from a data fetching function list
+    Uses the function list names as the keys, and their returned value as the values.
+
+    For example: You have a list of urls that contain the data you want to have access to.
+    You can write functions that bare the names you want to give to each dataset, and have the function
+    fetch the data from the url, extract the data from the response and possibly prepare it
+    (we advise minimally, since you can always transform from the raw source, but the opposite can be impossible).
+
+    >>> def foo():
+    ...     return 'bar'
+    >>> def pi():
+    ...     return 3.14159
+    >>> s = FuncReader([foo, pi])
+    >>> list(s)
+    ['foo', 'pi']
+    >>> s['foo']
+    'bar'
+    >>> s['pi']
+    3.14159
+    """
+
+    def __init__(self, funcs):
+        # TODO: assert no free arguments (arguments are allowed but must all have defaults)
+        self.funcs = funcs
+        self._func_of_name = {func.__name__: func for func in funcs}
+
+    def __contains__(self, k):
+        return k in self._func_of_name
+
+    def __iter__(self):
+        yield from self._func_of_name
+
+    def __len__(self):
+        return len(self._func_of_name)
+
+    def __getitem__(self, k):
+        return self._func_of_name[k]()  # call the func