LazyLoader

What it is

• A small utility class that defers creation of an underlying value until it is first accessed.
• Wraps a loader: Callable and proxies common operations to the loaded value.

Public API

• class LazyLoader(loader: Callable)
  • Holds:
    • loaded: bool - whether the value has been loaded.
    • loader: Callable - function used to compute/load the value.
    • value: Any - cached loaded value (set on first use).
• LazyLoader.__init__(loader: Callable)
  • Initializes in an unloaded state.
• LazyLoader.is_loaded() -> bool
  • Returns whether the underlying value has been loaded.
• LazyLoader.__getattr__(name)
  • Loads the value on first attribute access and forwards getattr(...).
• LazyLoader.__iter__()
  • Loads on first iteration and returns iter(value).
• LazyLoader.__len__()
  • Loads on first len(...) and returns len(value).
• LazyLoader.__getitem__(key)
  • Loads on first indexing and returns value[key].
• LazyLoader.__repr__()
  • Loads on first repr(...) and returns repr(value).

Configuration/Dependencies

• Depends on:
  • typing.Callable, typing.Any (type annotations only).
• No external configuration.

Usage

from naas_abi_core.utils.LazyLoader import LazyLoader

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

lazy = LazyLoader(load_data)

print(lazy.is_loaded())  # False
print(lazy["a"])         # triggers load, prints "loading...", then 1
print(lazy.is_loaded())  # True
print(repr(lazy))        # uses cached value

Caveats

• Accessing repr(lazy) will load the value (because __repr__ triggers loading).
• Only a subset of operations are proxied (__getattr__, iteration, length, indexing, repr). Other operations may not behave like the underlying value unless they route through these methods.