[P3][bug] Constructing OilPriceAPI emits ImportWarning when matplotlib is not installed

[karlwaldman]

Status

Confirmed on 2026-09-13 against origin/main 0266d08. Found while testing #149: a test that turns all warnings into errors failed when it built a sync client.

Defect

OilPriceAPI.__init__ (oilpriceapi/client.py:224-230) always constructs PriceVisualizer(self). PriceVisualizer.__init__ (oilpriceapi/visualization.py:92-97) calls warnings.warn("matplotlib is required for visualization. Install with: pip install matplotlib", ImportWarning) whenever matplotlib is not installed.

So every sync client built without the optional matplotlib extra warns about a feature the caller has not used.

• Python's default filters ignore ImportWarning, so plain scripts do not show it.
• Anything that surfaces warnings does show it: pytest's warning summary, -W error, and warnings.simplefilter("error"/"always").
• Under -W error or simplefilter("error"), client construction raises.

The except ImportError around the construction does not catch it, because a warning is not an ImportError.

Repro

import warnings
from oilpriceapi import OilPriceAPI

with warnings.catch_warnings():
    warnings.simplefilter("error")
    OilPriceAPI(api_key="-".join(["fixture", "not", "a", "real", "key"]))
# ImportWarning: matplotlib is required for visualization. Install with: pip install matplotlib

Run in an environment with the SDK installed and matplotlib absent.

Expected

Construction emits nothing. Warn, or raise an error that names the extra, only when a client.viz plotting method is actually called without matplotlib.