Defer heavy imports to speed up import time - #968
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traitlets and its core utils imported inspect (which pulls in ast, dis, tokenize, linecache), pathlib, and ast at module top level, and traitlets.config additionally imported logging.config (pulling logging.handlers, socket, pickle, dataclasses), pprint and json eagerly. All of these are only needed on cold paths (string parsing, filesystem Path traits, help/config-dump output, logging configuration at Application startup). Because the modules use `from __future__ import annotations`, annotations referring to these names are never evaluated at runtime, so the imports can be deferred to their actual (rare) use sites. inspect.isclass(x) is replaced with isinstance(x, type) (which is strictly identical since python 3) and inspect.currentframe() with sys._getframe() (which is the same on Cpython) to avoid needing inspect at all on the class-definition path.
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traitlets and its core utils imported inspect (which pulls in ast, dis, tokenize, linecache), pathlib, and ast at module top level, and traitlets.config additionally imported logging.config (pulling logging.handlers, socket, pickle, dataclasses), pprint and json eagerly. All of these are only needed on cold paths (string parsing, filesystem Path traits, help/config-dump output, logging configuration at Application startup). Because the modules use
from __future__ import annotations, annotations referring to these names are never evaluated at runtime, so the imports can be deferred to their actual (rare) use sites. inspect.isclass(x) is replaced with isinstance(x, type) (which is strictly identical since python 3) and inspect.currentframe() with sys._getframe() (which is the same on Cpython) to avoid needing inspect at all on the class-definition path.