Refactor dynamic base_url attribute on requests.Session

[gawbul]

Priority: High

Issue

The code dynamically adds a base_url attribute to requests.Session, which doesn't have this attribute by default. This creates a non-standard attribute through dynamic attribute assignment.

Current Code

# pyensemblrest/ensemblrest.py:123-124
for key, val in client_args_copy.items():
    if key in ("base_url", "proxies"):
        setattr(self.session, key, val)  # Adding base_url to requests.Session

# Later used as:
url = self.session.base_url + func["url"]  # type: ignore[attr-defined]

Problem

• Requires type ignore comments
• Non-standard use of requests.Session
• Harder to understand for maintainers
• May break with requests library updates

Recommendation

Store base_url as an instance attribute:

class EnsemblRest:
    def __init__(self, api_table: dict[str, Any] = ensembl_api_table, **kwargs: dict[str, Any]) -> None:
        self.base_url = kwargs.pop('base_url', ensembl_default_url)
        self.session_args = kwargs or {}
        # ... rest of init
        
    def call_api_func(self, api_call: str, api_table: dict[str, Any], **kwargs: dict[str, Any]) -> Any:
        # ...
        url = re.sub(
            r"\{\{(?P<m>[a-zA-Z1-9_]+)\}\}",
            lambda m: "%s" % kwargs.get(m.group(1)),
            self.base_url + func["url"],  # Use instance attribute
        )

Files to Update

• pyensemblrest/ensemblrest.py - Add self.base_url and remove dynamic attribute

Testing

• Run full test suite
• Verify custom base_url still works