Importer

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provide.foundation.utils.importer

Functions

lazy_import

lazy_import(parent_module: str, name: str) -> object

Import a module lazily with comprehensive safety checks.

This function provides thread-safe lazy loading with protection against: - Circular imports (tracks import chains) - Stack overflow (enforces maximum depth) - Corrupted module states (validates sys.modules)

Commonly lazy-loaded modules: - cli: Requires optional 'click' dependency - crypto: Cryptographic utilities - formatting: Text formatting utilities - metrics: Metrics collection - observability: Observability features

Parameters:

Name	Type	Description	Default
parent_module	str	The parent module name (e.g., "provide.foundation")	required
name	str	Module name to lazy-load (e.g., "cli")	required

Returns:

Type	Description
object	The imported module

Raises:

Type	Description
AttributeError	If module is not allowed for lazy loading or circular import detected
ImportError	If module import fails
RecursionError	If import depth exceeds safe limits

Note

Complexity is intentionally high to handle all edge cases in this critical import hook (recursion, corruption, depth limits).

Example

from provide.foundation.utils.importer import lazy_import cli = lazy_import("provide.foundation", "cli")

Source code in provide/foundation/utils/importer.py

def lazy_import(parent_module: str, name: str) -> object:
    """Import a module lazily with comprehensive safety checks.

    This function provides thread-safe lazy loading with protection against:
    - Circular imports (tracks import chains)
    - Stack overflow (enforces maximum depth)
    - Corrupted module states (validates sys.modules)

    Commonly lazy-loaded modules:
    - cli: Requires optional 'click' dependency
    - crypto: Cryptographic utilities
    - formatting: Text formatting utilities
    - metrics: Metrics collection
    - observability: Observability features

    Args:
        parent_module: The parent module name (e.g., "provide.foundation")
        name: Module name to lazy-load (e.g., "cli")

    Returns:
        The imported module

    Raises:
        AttributeError: If module is not allowed for lazy loading or circular import detected
        ImportError: If module import fails
        RecursionError: If import depth exceeds safe limits

    Note:
        Complexity is intentionally high to handle all edge cases
        in this critical import hook (recursion, corruption, depth limits).

    Example:
        >>> from provide.foundation.utils.importer import lazy_import
        >>> cli = lazy_import("provide.foundation", "cli")
    """
    # Build the full module name
    module_name = f"{parent_module}.{name}"

    # Initialize thread-local state if needed
    if not hasattr(_thread_local, "getattr_in_progress"):
        _thread_local.getattr_in_progress = set()
        _thread_local.import_depth = 0
        _thread_local.import_chain = []

    # Check recursion depth to prevent stack overflow from complex import chains
    if _thread_local.import_depth >= MAX_LAZY_IMPORT_DEPTH:
        chain_str = " -> ".join([*_thread_local.import_chain, name])
        raise RecursionError(
            f"Lazy import depth limit ({MAX_LAZY_IMPORT_DEPTH}) exceeded. "
            f"Import chain: {chain_str}. This indicates a complex nested import "
            f"that should be refactored or imported eagerly."
        )

    # Check if we've already entered recursion for this specific module
    # This prevents infinite loops when a module has been corrupted
    if name in _thread_local.getattr_in_progress:
        chain_str = " -> ".join([*_thread_local.import_chain, name])
        raise AttributeError(
            f"module '{parent_module}' has no attribute '{name}' "
            f"(circular import detected in chain: {chain_str}). "
            f"Module may be corrupted in sys.modules."
        )

    # Set recursion guards
    _thread_local.getattr_in_progress.add(name)
    _thread_local.import_depth += 1
    _thread_local.import_chain.append(name)

    try:
        # Check if module is already in sys.modules but corrupted
        if module_name in sys.modules:
            existing_module = sys.modules[module_name]
            # If it exists and is valid, return it
            if existing_module is not None:
                return existing_module
            # If it's None or invalid, remove it so we can re-import
            del sys.modules[module_name]

        # Import the submodule with appropriate error handling
        try:
            mod = __import__(module_name, fromlist=[""])
            sys.modules[module_name] = mod
            return mod
        except ImportError as e:
            # Provide helpful error messages for known optional dependencies
            if name in SPECIAL_MODULES:
                error_str = str(e)
                # Check if error is about missing dependency for this feature
                if (name == "cli" and "click" in error_str) or (name == "transport" and "httpx" in error_str):
                    raise ImportError(SPECIAL_MODULES[name]) from e
            raise
    finally:
        # Always clear recursion guards in reverse order
        _thread_local.getattr_in_progress.discard(name)
        _thread_local.import_depth -= 1
        if _thread_local.import_chain and _thread_local.import_chain[-1] == name:
            _thread_local.import_chain.pop()