Andrew/type checks on input

src/py/CHANGELOG.txt

@@ -1,6 +1,7 @@
 v1.0.0rc11
 - Write mocker tool to parameterize opts in tests
 - Crop page to pdf size
+- Add type checks to user input for improved error messages
 v1.0.0rc10
 - Allow user to pass Figure-like dicts
 - Fix bug by which calc fig rejected plotly figures

src/py/kaleido/_fig_tools.py

@@ -14,9 +14,14 @@
 
 
 def _is_figurish(o):
-    return hasattr(o, "to_dict") or (
-        isinstance(o, dict) and "data" in o and "layout" in o
-    )
+    valid = hasattr(o, "to_dict") or (isinstance(o, dict) and "data" in o)
+    if not valid:
+        _logger.debug(
+            f"Figure has to_dict? {hasattr(o, 'to_dict')} "
+            f"is dict? {isinstance(o, dict)} "
+            f"Keys: {o.keys() if hasattr(o, 'keys') else None!s}",
+        )
+    return valid
 
 
 def _get_figure_dimensions(layout, width, height):
@@ -56,6 +61,16 @@ def to_spec(figure, layout_opts):
     # Get figure layout
     layout = figure.get("layout", {})
 
+    for k, v in layout_opts.items():
+        if k == "format":
+            if v is not None and not isinstance(v, (str)):
+                raise TypeError(f"{v} must be string or None")
+        elif k in ("scale", "height", "width"):
+            if v is not None and not isinstance(v, (float, int)):
+                raise TypeError(f"{v} must be numeric or None")
+        else:
+            raise AttributeError(f"Unknown key in layout options, {k}")
+
     # Extract info
     extension = _get_format(layout_opts.get("format") or DEFAULT_EXT)
     width, height = _get_figure_dimensions(
@@ -86,15 +101,20 @@ def _next_filename(path, prefix, ext):
     return f"{prefix}.{ext}" if n == 1 else f"{prefix}-{n}.{ext}"
 
 
-def build_fig_spec(fig, path, opts):
+def build_fig_spec(fig, path, opts):  #  noqa: C901
     if not opts:
         opts = {}
 
+    if not _is_figurish(fig):
+        raise TypeError("Figure supplied doesn't seem to be a valid plotly figure.")
+
     if hasattr(fig, "to_dict"):
         fig = fig.to_dict()
 
     if isinstance(path, str):
         path = Path(path)
+    elif path and not isinstance(path, Path):
+        raise TypeError("Path should be a string or `pathlib.Path` object (or None)")
 
     if path and path.suffix and not opts.get("format"):
         opts["format"] = path.suffix.lstrip(".")