D4Vinci/Scrapling · error · TypeError

strategy must be callable, got {type(strategy).__name__}

Error message

strategy must be callable, got {type(strategy).__name__}

What it means

Raised by `ProxyRotator.__init__` when the `strategy` argument is not callable. The rotation strategy is a function taking (proxies, current_index) and returning (proxy, next_index); passing anything that cannot be called (a string name, a number, None) fails this check.

Source

Thrown at scrapling/engines/toolbelt/proxy_rotation.py:68

    def __init__(
        self,
        proxies: List[ProxyType],
        strategy: RotationStrategy = cyclic_rotation,
    ):
        """
        Initialize the proxy rotator.

        :param proxies: List of proxy URLs or Playwright-style proxy dicts.
            - String format: "http://proxy1:8080" or "http://user:pass@proxy:8080"
            - Dict format: {"server": "http://proxy:8080", "username": "user", "password": "pass"}
        :param strategy: Rotation strategy function. Takes (proxies, current_index) and returns (proxy, next_index). Defaults to cyclic_rotation.
        """
        if not proxies:
            raise ValueError("At least one proxy must be provided")

        if not callable(strategy):
            raise TypeError(f"strategy must be callable, got {type(strategy).__name__}")

        self._strategy = strategy
        self._lock = Lock()

        # Validate and store proxies
        self._proxies: List[ProxyType] = []
        self._proxy_to_index: Dict[str, int] = {}  # O(1) lookup by unique key (server + username)
        for i, proxy in enumerate(proxies):
            if isinstance(proxy, (str, dict)):
                if isinstance(proxy, dict) and "server" not in proxy:
                    raise ValueError("Proxy dict must have a 'server' key")

                self._proxy_to_index[_get_proxy_key(proxy)] = i
                self._proxies.append(proxy)
            else:
                raise TypeError(f"Invalid proxy type: {type(proxy)}. Expected str or dict.")

        self._current_index = 0

View on GitHub (pinned to 5d213a2d47)

Solutions

  1. Pass the function object itself: from scrapling.engines.toolbelt.proxy_rotation import random_rotation; ProxyRotator(proxies, strategy=random_rotation).
  2. If config gives a string, map it to the function first: strategies = {'random': random_rotation, 'cyclic': cyclic_rotation}.
  3. Do not add parentheses after the strategy name when passing it.

Example fix

# before
rotator = ProxyRotator(proxies, strategy='random_rotation')

# after
from scrapling.engines.toolbelt.proxy_rotation import random_rotation
rotator = ProxyRotator(proxies, strategy=random_rotation)
Defensive patterns

Strategy: type-guard

Validate before calling

assert callable(strategy), f"strategy must be a function, got {type(strategy).__name__}"
rotator = ProxyRotator(proxies=pool, strategy=strategy)

Type guard

from typing import Any, Callable

def is_rotation_strategy(value: Any) -> bool:
    return callable(value) and not isinstance(value, (str, bytes))

Try / catch

try:
    ProxyRotator(pool, strategy=strategy)
except TypeError as e:
    if "strategy must be callable" in str(e):
        from scrapling.engines.toolbelt.proxy_rotation import cyclic_rotation
        strategy = cyclic_rotation  # safe default
    else:
        raise

Prevention

When it happens

Trigger: ProxyRotator(proxies=pool, strategy='random') (passing the name instead of a function), strategy=None, or strategy=random_rotation() (calling the function and passing its result instead of the function itself).

Common situations: Config files storing the strategy as a string that is passed through verbatim; accidentally invoking the strategy with () at the call site; copy-pasting example code that instantiates instead of references.

Related errors

AI-assisted analysis of D4Vinci/Scrapling@5d213a2d47 (2026-08-14). Data as JSON: /api/errors/6b2f2be2f07033ad. Report an issue: GitHub.