LazyLoader

What it is

• LazyLoader defers creation of an underlying value until it’s first used.
• It wraps a zero-argument loader callable and forwards common operations to the loaded value.

Public API

• class LazyLoader(loader: Callable)
  • __init__(loader)
    • Stores the loader and marks the instance as not yet loaded.
  • is_loaded() -> bool
    • Returns whether the underlying value has been loaded.
  • __getattr__(name)
    • On first attribute access, calls loader() once, then forwards getattr to the loaded value.
  • __iter__()
    • Loads on first iteration, then returns iter(loaded_value).
  • __len__()
    • Loads on first len(...), then returns len(loaded_value).
  • __getitem__(key)
    • Loads on first indexing, then returns loaded_value[key].
  • __repr__()
    • Loads on first repr(...), then returns repr(loaded_value).

Configuration/Dependencies

• Depends on Python’s standard library: typing.Callable, typing.Any.
• loader must be callable and is invoked as loader() (no arguments).

Usage

from naas_abi_core.utils.LazyLoader import LazyLoader

def load_data():
    return {"a": 1, "b": 2}

lazy = LazyLoader(load_data)

print(lazy.is_loaded())   # False
print(lazy["a"])          # Triggers load, then returns 1
print(lazy.is_loaded())   # True
print(repr(lazy))         # Uses loaded value

Caveats

• Loading happens on first use of: attribute access, iteration, len(), indexing, or repr().
• repr(lazy) triggers loading (it does not show an “unloaded” placeholder).
• The loader is called at most once; subsequent operations reuse the stored value.