Quantity as an actual class, rather than factory

doc/api.rst

@@ -279,10 +279,10 @@ Top-level classes and functions
    <foo:a-b-c>
 
 
-.. autodata:: genno.Quantity(data, *args, **kwargs)
-   :annotation:
+.. autoclass:: genno.Quantity
+   :members:
 
-The :data:`.Quantity` constructor converts its arguments to an internal, :class:`xarray.DataArray`-like data format:
+The :class:`.Quantity` constructor converts its arguments to an internal, :class:`xarray.DataArray`-like data format:
 
 .. code-block:: python
 
@@ -307,9 +307,7 @@ Computations
 .. automodule:: genno.computations
    :members:
 
-   Unless otherwise specified, these methods accept and return
-   :class:`Quantity <genno.utils.Quantity>` objects for data
-   arguments/return values.
+   Unless otherwise specified, these methods accept and return :class:`.Quantity` objects for data arguments/return values.
 
    Genno's :ref:`compatibility modules <compat>` each provide additional computations.
 

doc/conf.py

@@ -23,6 +23,7 @@
     "sphinx.ext.intersphinx",
     "sphinx.ext.napoleon",
     "sphinx.ext.todo",
+    "sphinx.ext.viewcode",
 ]
 
 # Add any paths that contain templates here, relative to this directory.
@@ -60,6 +61,7 @@
     "dask": ("https://docs.dask.org/en/stable/", None),
     "ixmp": ("https://docs.messageix.org/projects/ixmp/en/latest", None),
     "message_ix": ("https://docs.messageix.org/en/latest", None),
+    "pandas": ("https://pandas.pydata.org/docs/", None),
     "pint": ("https://pint.readthedocs.io/en/stable/", None),
     "plotnine": ("https://plotnine.readthedocs.io/en/stable/", None),
     "pyam": ("https://pyam-iamc.readthedocs.io/en/stable/", None),

doc/whatsnew.rst

@@ -6,8 +6,14 @@ What's new
    :backlinks: none
    :depth: 1
 
-.. Next release
-.. ============
+Next release
+============
+
+- :class:`.Quantity` becomes an actual class, rather than a factory function; :class:`.AttrSeries` and :class:`.SparseDataArray` are subclasses (:pull:`37`).
+- :class:`.AttrSeries` gains methods :meth:`~.AttrSeries.bfill`, :meth:`~.AttrSeries.cumprod`, :meth:`~.AttrSeries.ffill`, and :meth:`~.AttrSeries.shift` (:pull:`37`)
+- :func:`.computations.load_file` uses the `skipinitialspace` parameter to :func:`pandas.read_csv`; extra dimensions not mentioned in the `dims` parameter are preserved (:pull:`37`).
+- :meth:`.AttrSeries.sel` accepts :class:`xarray.DataArray` for xarray-style indexing (:pull:`37`).
+
 
 v1.1.1 (2021-02-22)
 ===================

genno/computations.py

@@ -9,8 +9,9 @@
 import pandas as pd
 import pint
 
-from .core.quantity import Quantity, assert_quantity
-from .util import collect_units, filter_concat_args
+from genno.core.attrseries import AttrSeries
+from genno.core.quantity import Quantity, assert_quantity
+from genno.util import collect_units, filter_concat_args
 
 __all__ = [
     "add",
@@ -55,12 +56,12 @@ def add(*quantities, fill_value=0.0):
     # Ensure arguments are all quantities
     assert_quantity(*quantities)
 
-    if Quantity.CLASS == "SparseDataArray":
-        # Use xarray's built-in broadcasting, return to Quantity class
-        quantities = map(Quantity, xr.broadcast(*quantities))
-    else:
+    if isinstance(quantities[0], AttrSeries):
         # map() returns an iterable
         quantities = iter(quantities)
+    else:
+        # Use xarray's built-in broadcasting, return to Quantity class
+        quantities = map(Quantity, xr.broadcast(*quantities))
 
     # Initialize result values with first entry
     result = next(quantities)
@@ -74,7 +75,7 @@ def add(*quantities, fill_value=0.0):
 
         factor = u.from_(1.0, strict=False).to(ref_unit).magnitude
 
-        if Quantity.CLASS == "AttrSeries":
+        if isinstance(q, AttrSeries):
             result = result.add(factor * q, fill_value=fill_value).dropna()
         else:
             result = result + factor * q
@@ -89,12 +90,12 @@ def aggregate(quantity, groups, keep):
     ----------
     quantity : :class:`Quantity <genno.utils.Quantity>`
     groups: dict of dict
-        Top-level keys are the names of dimensions in `quantity`. Second-level
-        keys are group names; second-level values are lists of labels along the
-        dimension to sum into a group.
+        Top-level keys are the names of dimensions in `quantity`. Second-level keys are
+        group names; second-level values are lists of labels along the dimension to sum
+        into a group.
     keep : bool
-        If True, the members that are aggregated into a group are returned with
-        the group sums. If False, they are discarded.
+        If True, the members that are aggregated into a group are returned with the
+        group sums. If False, they are discarded.
 
     Returns
     -------
@@ -113,7 +114,8 @@ def aggregate(quantity, groups, keep):
             agg = (
                 quantity.sel({dim: members}).sum(dim=dim).assign_coords(**{dim: group})
             )
-            if Quantity.CLASS == "AttrSeries":
+
+            if isinstance(agg, AttrSeries):
                 # .transpose() is necessary for AttrSeries
                 agg = agg.transpose(*quantity.dims)
             else:
@@ -220,8 +222,8 @@ def combine(*quantities, select=None, weights=None):  # noqa: F811
     # Check units
     units = collect_units(*quantities)
     for u in units:
-        # TODO relax this condition: modify the weights with conversion factors
-        #      if the units are compatible, but not the same
+        # TODO relax this condition: modify the weights with conversion factors if the
+        #      units are compatible, but not the same
         if u != units[0]:
             raise ValueError(f"Cannot combine() units {units[0]} and {u}")
     units = units[0]
@@ -247,16 +249,27 @@ def combine(*quantities, select=None, weights=None):  # noqa: F811
 
 
 def concat(*objs, **kwargs):
-    """Concatenate Quantity *objs*.
+    """Concatenate Quantity `objs`.
 
-    Any strings included amongst *args* are discarded, with a logged warning;
-    these usually indicate that a quantity is referenced which is not in the
-    Computer.
+    Any strings included amongst `objs` are discarded, with a logged warning; these
+    usually indicate that a quantity is referenced which is not in the Computer.
     """
     objs = filter_concat_args(objs)
-    if Quantity.CLASS == "AttrSeries":
-        # Silently discard any "dim" keyword argument
-        kwargs.pop("dim", None)
+    if Quantity._get_class() is AttrSeries:
+        try:
+            # Retrieve a "dim" keyword argument
+            dim = kwargs.pop("dim")
+        except KeyError:
+            pass
+        else:
+            if isinstance(dim, pd.Index):
+                # Convert a pd.Index argument to names and keys
+                kwargs["names"] = [dim.name]
+                kwargs["keys"] = dim.values
+            else:
+                # Something else; warn and discard
+                log.warning(f"Ignore concat(…, dim={repr(dim)})")
+
         return pd.concat(objs, **kwargs)
     else:
         # Correct fill-values
@@ -284,22 +297,22 @@ def group_sum(qty, group, sum):
 def load_file(path, dims={}, units=None, name=None):
     """Read the file at *path* and return its contents as a :class:`.Quantity`.
 
-    Some file formats are automatically converted into objects for direct use
-    in genno computations:
+    Some file formats are automatically converted into objects for direct use in genno
+    computations:
 
     :file:`.csv`:
-       Converted to :class:`.Quantity`. CSV files must have a 'value' column;
-       all others are treated as indices, except as given by `dims`. Lines
-       beginning with '#' are ignored.
+       Converted to :class:`.Quantity`. CSV files must have a 'value' column; all others
+       are treated as indices, except as given by `dims`. Lines beginning with '#' are
+       ignored.
 
     Parameters
     ----------
     path : pathlib.Path
         Path to the file to read.
     dims : collections.abc.Collection or collections.abc.Mapping, optional
-        If a collection of names, other columns besides these and 'value' are
-        discarded. If a mapping, the keys are the column labels in `path`, and
-        the values are the target dimension names.
+        If a collection of names, other columns besides these and 'value' are discarded.
+        If a mapping, the keys are the column labels in `path`, and the values are the
+        target dimension names.
     units : str or pint.Unit
         Units to apply to the loaded Quantity.
     name : str
@@ -308,7 +321,7 @@ def load_file(path, dims={}, units=None, name=None):
     # TODO optionally cache: if the same Computer is used repeatedly, then the file will
     #      be read each time; instead cache the contents in memory.
     if path.suffix == ".csv":
-        data = pd.read_csv(path, comment="#")
+        data = pd.read_csv(path, comment="#", skipinitialspace=True)
 
         # Index columns
         index_columns = data.columns.tolist()
@@ -324,26 +337,26 @@ def load_file(path, dims={}, units=None, name=None):
             # Use a unique value for units of the quantity
             if len(units_col) > 1:
                 raise ValueError(
-                    f"Cannot load {path} with non-unique units " + repr(units_col)
+                    f"Cannot load {path} with non-unique units {repr(units_col)}"
                 )
             elif units and units not in units_col:
                 raise ValueError(
-                    f"Explicit units {units} do not match " f"{units_col[0]} in {path}"
+                    f"Explicit units {units} do not match {units_col[0]} in {path}"
                 )
             units = units_col[0]
 
         if len(dims):
-            # Use specified dimensions
-            if not isinstance(dims, Mapping):
-                # Convert a list, set, etc. to a dict
-                dims = {d: d for d in dims}
+            # Convert a list, set, etc. to a dict
+            dims = dims if isinstance(dims, Mapping) else {d: d for d in dims}
 
             # - Drop columns not mentioned in *dims*
             # - Rename columns according to *dims*
             data = data.drop(columns=set(index_columns) - set(dims.keys())).rename(
                 columns=dims
             )
-            index_columns = list(dims.values())
+
+            index_columns = list(data.columns)
+            index_columns.pop(index_columns.index("value"))
 
         return Quantity(data.set_index(index_columns)["value"], units=units, name=name)
     elif path.suffix in (".xls", ".xlsx"):
@@ -381,7 +394,7 @@ def pow(a, b):
     if not u_b.dimensionless:
         raise ValueError(f"Cannot raise to a power with units ({u_b:~})")
 
-    if Quantity.CLASS == "AttrSeries":
+    if isinstance(a, AttrSeries):
         result = a ** b.align_levels(a)
     else:
         result = a ** b
@@ -405,7 +418,7 @@ def product(*quantities):
 
     # Iterate over remaining entries
     for q, u in items:
-        if Quantity.CLASS == "AttrSeries":
+        if isinstance(q, AttrSeries):
             # Work around pandas-dev/pandas#25760; see attrseries.py
             result = (result * q.align_levels(result)).dropna()
         else:
@@ -428,7 +441,7 @@ def ratio(numerator, denominator):
     # Handle units
     u_num, u_denom = collect_units(numerator, denominator)
 
-    if Quantity.CLASS == "AttrSeries":
+    if isinstance(numerator, AttrSeries):
         result = numerator / denominator.align_levels(numerator)
     else:
         result = numerator / denominator
@@ -439,12 +452,16 @@ def ratio(numerator, denominator):
     ureg = pint.get_application_registry()
     result.attrs["_unit"] = ureg.Unit(u_num) / ureg.Unit(u_denom)
 
-    if Quantity.CLASS == "AttrSeries":
+    if isinstance(result, AttrSeries):
         result.dropna(inplace=True)
 
     return result
 
 
+#: TODO make this the actual method name; emit DeprecationWarning if ratio() is used
+div = ratio
+
+
 def select(qty, indexers, inverse=False):
     """Select from *qty* based on *indexers*.