Adds documentation/examples for data adapters

This has:
1. A reference table, automatically generated using a custom sphinx
   directive
2. References for the base classes for extension

Re (1) we generate a bare-bones table but it should be enough. For now,
we just link to the code, but we will, at some point, link to actual
class docs.

docs/conf.py

@@ -30,6 +30,7 @@
     "sphinx.ext.autosummary",
     "myst_parser",
     "sphinx_sitemap",
+    "docs.data_adapters_extension",
 ]
 
 # for the sitemap extension ---

docs/data_adapters_extension.py

@@ -0,0 +1,288 @@
+import dataclasses
+import inspect
+import os
+from typing import List, Optional, Tuple, Type
+
+import git
+from docutils import nodes
+from docutils.parsers.rst import Directive
+
+import hamilton.io.data_adapters
+from hamilton import registry
+
+"""A module to crawl available data adapters and generate documentation for them.
+Note these currently link out to the source code on GitHub, but they should
+be linking to the documentation instead, which hasn't been generated yet.
+"""
+
+# These have fallbacks for local dev
+GIT_URL = os.environ.get("READTHEDOCS_GIT_CLONE_URL", "https://github.com/dagworks-inc/hamilton")
+GIT_ID = os.environ.get("READTHEDOCS_GIT_IDENTIFIER", "main")
+
+# All the modules that register data adapters
+# When you register a new one, add it here
+MODULES_TO_IMPORT = ["hamilton.io.default_data_loaders", "hamilton.plugins.pandas_extensions"]
+
+for module in MODULES_TO_IMPORT:
+    __import__(module)
+
+
+def get_git_root(path: str) -> str:
+    """Yields the git room of a repo, given an absolute path to
+    a file within the repo.
+
+    :param path: Path to a file within a git repo
+    :return:  The root of the git repo
+    """
+    git_repo = git.Repo(path, search_parent_directories=True)
+    git_root = git_repo.git.rev_parse("--show-toplevel")
+    return git_root
+
+
+@dataclasses.dataclass
+class Param:
+    name: str
+    type: str
+    default: Optional[str] = None
+
+
+def get_default(param: dataclasses.Field) -> Optional[str]:
+    """Gets the deafult of a dataclass field, if it has one.
+
+    :param param:  The dataclass field
+    :return: The str representation of the default.
+    """
+    if param.default is dataclasses.MISSING:
+        return None
+    return str(param.default)
+
+
+def get_lines_for_class(class_: Type[Type]) -> Tuple[int, int]:
+    """Gets the set of lines in which a class is implemented
+
+    :param class_: The class to get the lines for
+    :return: A tuple of the start and end lines
+    """
+    lines = inspect.getsourcelines(class_)
+    start_line = lines[1]
+    end_line = lines[1] + len(lines[0])
+    return start_line, end_line
+
+
+def get_class_repr(class_: Type) -> str:
+    """Gets a representation of a class that can be used in documentation.
+
+    :param class_: Python class to get the representation for
+    :return: Str representation
+    """
+
+    try:
+        return class_.__qualname__
+    except AttributeError:
+        # This happens when we have generics or other oddities
+        return str(class_)
+
+
+@dataclasses.dataclass
+class AdapterInfo:
+    key: str
+    class_name: str
+    class_path: str
+    load_params: List[Param]
+    save_params: List[Param]
+    applicable_types: List[str]
+    file_: str
+    line_nos: Tuple[int, int]
+
+    @staticmethod
+    def from_loader(loader: Type[hamilton.io.data_adapters.DataLoader]) -> "AdapterInfo":
+        """Utility constructor to create the AdapterInfo from a DataLoader class
+
+        :param loader: DataLoader class
+        :return: AdapterInfo derived from it
+        """
+
+        return AdapterInfo(
+            key=loader.name(),
+            class_name=loader.__name__,
+            class_path=loader.__module__,
+            load_params=[
+                Param(name=p.name, type=get_class_repr(p.type), default=get_default(p))
+                for p in dataclasses.fields(loader)
+            ]
+            if issubclass(loader, hamilton.io.data_adapters.DataSaver)
+            else None,
+            save_params=[
+                Param(name=p.name, type=get_class_repr(p.type), default=get_default(p))
+                for p in dataclasses.fields(loader)
+            ]
+            if issubclass(loader, hamilton.io.data_adapters.DataSaver)
+            else None,
+            applicable_types=[get_class_repr(t) for t in loader.applicable_types()],
+            file_=inspect.getfile(loader),
+            line_nos=get_lines_for_class(loader),
+        )
+
+
+def _collect_loaders(saver_or_loader: str) -> List[Type[hamilton.io.data_adapters.AdapterCommon]]:
+    """Collects all loaders from the registry.
+
+    :return:
+    """
+    out = []
+    loaders = (
+        list(registry.LOADER_REGISTRY.values())
+        if saver_or_loader == "loader"
+        else list(registry.SAVER_REGISTRY.values())
+    )
+    for classes in loaders:
+        for cls in classes:
+            if cls not in out:
+                out.append(cls)
+    return out
+
+
+# Utility functions to render different components of the adapter in table cells
+
+
+def render_key(key: str):
+    return [nodes.Text(key, key)]
+
+
+def render_class_name(class_name: str):
+    return [nodes.literal(text=class_name)]
+
+
+def render_class_path(class_path: str, file_: str, line_start: int, line_end: int):
+    git_path = get_git_root(file_)
+    file_relative_to_git_root = os.path.relpath(file_, git_path)
+    href = f"{GIT_URL}/blob/{GIT_ID}/{file_relative_to_git_root}#L{line_start}-L{line_end}"
+    # href = f"{GIT_URL}/blob/{GIT_ID}/{file_}#L{line_no}"
+    return [nodes.raw("", f'<a href="{href}">{class_path}</a>', format="html")]
+
+
+def render_adapter_params(load_params: Optional[List[Param]]):
+    if load_params is None:
+        return nodes.raw("", "<div/>", format="html")
+    fieldlist = nodes.field_list()
+    for i, load_param in enumerate(load_params):
+        fieldname = nodes.Text(load_param.name)
+        fieldbody = nodes.literal(
+            text=load_param.type
+            + ("=" + load_param.default if load_param.default is not None else "")
+        )
+        field = nodes.field("", fieldname, fieldbody)
+        fieldlist += field
+        if i < len(load_params) - 1:
+            fieldlist += nodes.raw("", "<br/>", format="html")
+    return fieldlist
+
+
+def render_applicable_types(applicable_types: List[str]):
+    fieldlist = nodes.field_list()
+    for applicable_type in applicable_types:
+        fieldlist += nodes.field("", nodes.literal(text=applicable_type), nodes.Text(""))
+        fieldlist += nodes.raw("", "<br/>", format="html")
+    return fieldlist
+
+
+class DataAdapterTableDirective(Directive):
+    """Custom directive to render a table of all data adapters. Takes in one argument
+    that is either 'loader' or 'saver' to indicate which adapters to render."""
+
+    has_content = True
+    required_arguments = 1  # Number of required arguments
+
+    def run(self):
+        """Runs the directive. This does the following:
+        1. Collects all loaders from the registry
+        2. Creates a table with the following columns:
+            - Key
+            - Class name
+            - Class path
+            - Load params
+            - Applicable types
+        3. Returns the table
+        :return: A list of nodes that Sphinx will render, consisting of the table node
+        """
+        saver_or_loader = self.arguments[0]
+        if saver_or_loader not in ("loader", "saver"):
+            raise ValueError(
+                f"loader_or_saver must be one of 'loader' or 'saver', " f"got {saver_or_loader}"
+            )
+        table_data = [
+            AdapterInfo.from_loader(loader) for loader in _collect_loaders(saver_or_loader)
+        ]
+
+        # Create the table and add columns
+        table_node = nodes.table()
+        tgroup = nodes.tgroup(cols=6)
+        table_node += tgroup
+
+        # Create columns
+        key_spec = nodes.colspec(colwidth=1)
+        # class_spec = nodes.colspec(colwidth=1)
+        load_params_spec = nodes.colspec(colwidth=2)
+        applicable_types_spec = nodes.colspec(colwidth=1)
+        class_path_spec = nodes.colspec(colwidth=1)
+
+        tgroup += [key_spec, load_params_spec, applicable_types_spec, class_path_spec]
+
+        # Create the table body
+        thead = nodes.thead()
+        row = nodes.row()
+
+        # Create entry nodes for each cell
+        key_entry = nodes.entry()
+        load_params_entry = nodes.entry()
+        applicable_types_entry = nodes.entry()
+        class_path_entry = nodes.entry()
+
+        key_entry += nodes.paragraph(text="key")
+
+        load_params_entry += nodes.paragraph(text=f"{saver_or_loader} params")
+        applicable_types_entry += nodes.paragraph(text="types")
+        class_path_entry += nodes.paragraph(text="module")
+
+        row += [key_entry, load_params_entry, applicable_types_entry, class_path_entry]
+        thead += row
+        tgroup += thead
+        tbody = nodes.tbody()
+        tgroup += tbody
+
+        # Populate table rows based on your table_data
+        for row_data in table_data:
+            row = nodes.row()
+
+            # Create entry nodes for each cell
+            key_entry = nodes.entry()
+            load_params_entry = nodes.entry()
+            applicable_types_entry = nodes.entry()
+            class_path_entry = nodes.entry()
+
+            # Create a paragraph node for each entry
+            # import pdb
+            # pdb.set_trace()
+            # para1 = nodes.literal(text=row_data['column1_data'])
+            # para2 = nodes.paragraph(text=row_data['column2_data'])
+
+            # Add the paragraph nodes to the entry nodes
+            key_entry += render_key(row_data.key)
+            load_params_entry += render_adapter_params(row_data.load_params)
+            applicable_types_entry += render_applicable_types(row_data.applicable_types)
+            class_path_entry += render_class_path(
+                row_data.class_path, row_data.file_, *row_data.line_nos
+            )
+
+            # Add the entry nodes to the row
+            row += [key_entry, load_params_entry, applicable_types_entry, class_path_entry]
+
+            # Add the row to the table body
+            tbody += row
+
+        return [table_node]
+
+
+def setup(app):
+    """Required to register the extension"""
+    app.add_directive("data_adapter_table", DataAdapterTableDirective)

docs/index.md

@@ -41,6 +41,7 @@ contributing
 
 reference/decorators/index
 reference/drivers/index
+reference/io/index
 reference/graph-adapters/index
 reference/result-builders/index
 reference/miscellaneous/index

docs/reference/io/adapter-documentation.rst

@@ -0,0 +1,20 @@
+=========================
+Data Adapters
+=========================
+
+Reference for data adapter base classes:
+
+.. autoclass:: hamilton.io.data_adapters.DataLoader
+   :special-members: __init__
+   :members:
+   :inherited-members:
+
+.. autoclass:: hamilton.io.data_adapters.DataSaver
+   :special-members: __init__
+   :members:
+   :inherited-members:
+
+.. autoclass:: hamilton.io.data_adapters.AdapterCommon
+   :special-members: __init__
+   :members:
+   :inherited-members:

docs/reference/io/available-data-adapters.rst

@@ -0,0 +1,56 @@
+========================
+Using Data Adapters
+========================
+
+This is an index of all the available data adapters, both savers and loaders.
+Note that some savers and loaders are the same (certain classes can handle both),
+but some are different. You will want to reference this when calling out to any of the following:
+
+1. Using :doc:`/reference/decorators/save_to/`.
+2. Using :doc:`/reference/decorators/load_from/`.
+3. Using :doc:`materialize </reference/drivers/Driver/>`
+
+To read these tables, you want to first look at the key to determine which format you want --
+these should be human-readable and familiar to you. Then you'll want to look at the `types` field
+to figure out which is the best for your case (the object you want to load from or save to).
+
+Finally, look up the adapter params to see what parameters you can pass to the data adapters.
+The optional params come with their default value specified.
+
+If you want more information, click on the `module`, it will send you to the code that implements
+it to see how the parameters are used.
+
+As an example, say we wanted to save a pandas dataframe to a CSV file. We would first find the
+key `csv`, which would inform us that we want to call `save_to.csv` (or `to.csv` in the case
+of `materialize`). Then, we would look at the `types` field, finding that there is a pandas
+dataframe adapter. Finally, we would look at the `params` field, finding that we can pass
+`path`, and (optionally) `sep` (which we'd realize defaults to `,` when looking at the code).
+
+All together, we'd end up with:
+
+.. code-block:: python
+
+    import pandas as pd
+    from hamilton.function_modifiers import value, save_to
+
+    @save_to.csv(path=value("my_file.csv"))
+    def my_data(...) -> pd.DataFrame:
+        ...
+
+And we're good to go!
+
+If you want to extend these, see :doc:`/reference/io/available-data-adapters` for documentation,
+and `the example <https://github.com/DAGWorks-Inc/hamilton/blob/main/examples/materialization/README.md>`_
+in the repository for an example of how to do so.
+
+=============
+Data Loaders
+=============
+
+.. data_adapter_table:: loader
+
+=============
+Data Savers
+=============
+
+.. data_adapter_table:: saver

docs/reference/io/index.rst

@@ -0,0 +1,11 @@
+==============
+I/O
+==============
+
+This section contains any information about I/O within Hamilton
+
+.. toctree::
+   :maxdepth: 2
+
+   available-data-adapters
+   adapter-documentation