Lazy imports based on __import__

[jdemeyer]

Implement lazy imports by overriding import.

To be used as

from sage.misc.lazy_import import _lazyimport_

with _lazyimport_:
    from sage.all import ZZ

Unlike the existing lazy import implementation, this supports both Python and Cython.

Depends on #22755

Component: misc

Author: Jeroen Demeyer

Branch/Commit: u/jdemeyer/ticket/22752 @ 9e1208b

Issue created by migration from https://trac.sagemath.org/ticket/22752

[jdemeyer]

Description changed:

--- 
+++ 
@@ -1,3 +1,3 @@
 Highly experimental...
 
-try to implement lazy imports using [PEP 302](https://www.python.org/dev/peps/pep-0302/) somehow.
+try to implement lazy imports by overriding [__import__](https://docs.python.org/3/library/functions.html#__import__) inside a context.

[jdemeyer]

Dependencies: #22755

[jdemeyer]

Branch: u/jdemeyer/ticket/22752

[jdemeyer]

Upstream: Reported upstream. No feedback yet.

[jdemeyer]

Commit: 06c4d0f

[jdemeyer]

Description changed:

--- 
+++ 
@@ -1,3 +1,10 @@
-Highly experimental...
+Implement lazy imports by overriding [__import__](https://docs.python.org/3/library/functions.html#__import__) inside a context.
 
-try to implement lazy imports by overriding [__import__](https://docs.python.org/3/library/functions.html#__import__) inside a context.
+To be used as
+
+```
+with lazyimport:
+    from sage.all import ZZ
+```
+
+We need a trivial Cython patch: https://github.com/cython/cython/pull/1660

[jdemeyer]

New commits:

94302ca	Do not declare functions/methods as "cdef inline"
9e5715e	Various improvements to lazy imports
d2bb491	Whitespace fix
06c4d0f	Lazy imports based on __import__

[sagetrac-git]

Changed commit from 06c4d0f to 8ec9f5d

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

8aac18a	Various improvements to lazy imports
8ec9f5d	Lazy import context based on __import__

[jdemeyer]

Changed upstream from Reported upstream. No feedback yet. to Fixed upstream, but not in a stable release.