get_lazy_attribute

FunctionPrivateSource

attr: Any | None = get_lazy_attribute(
    module: ModuleType, attr: str, parent: str
)

Get an attribute of a lazy module. This attribute will not be loaded if it is not accessed.

If the provided module is invalid, will return None.

danger

Note that the attribute returned by this function needs to be a callable one. To be specific, this function is mainly designed for getting a lazy-loaded class from a lazy-loaded module.

Arguments

Requires

Argument	Type	Required	Description
module	ModuleType		The lazy module where the attribute will be accessed.
attr	str		The attribute name used for locating the attribute.
parent	str		The name of the parent module where the attribute will be attached.

Returns

Argument	Type	Description
attr	Any | None	A lazy callable attribute. If it is not called, the attribtue will not be loaded. If the attribute cannot be located, return None.

Example

Load a class only when it is accessed

Codes

lazy_load_a_class.py

from typing import TYPE_CHECKING
from syncstream import utils

if TYPE_CHECKING:
    import html
    import html.parser as hparser
    from html.parser import HTMLParser
else:
    html = utils.lazy_import("html", package=None)
    hparser = utils.lazy_import("parser", package="html", dependencies=("html",))
    HTMLParser = utils.get_lazy_attribute(hparser, "HTMLParser", __name__)


print(html, hparser)
print(HTMLParser)
print(html, hparser)
print(HTMLParser())
print(html, hparser)

Results

<LazyModule html from "/usr/local/lib/python3.12/html/__init__.py"> <LazyModule html.parser from "/usr/local/lib/python3.12/html/parser.py">
<LazyAttribute HTMLParser from "html.parser">
<LazyModule html from "/usr/local/lib/python3.12/html/__init__.py"> <LazyModule html.parser from "/usr/local/lib/python3.12/html/parser.py">
<html.parser.HTMLParser object at 0x7f4416dfb380>
<module 'html' from '/usr/local/lib/python3.12/html/__init__.py'> <module 'html.parser' from '/usr/local/lib/python3.12/html/parser.py'>