Replace startup exception by warning

[tobiasdiez]

Since #22755, when lazy_import is used during startup, a runtime exception is thrown. This leads to problems if you want to use code with lazy imports in a library mode (e.g. in standalone tests or python scripts).

To support these use cases, this ticket replaces the exception to a print (which matches other warnings printed by the same code).

CC: @mkoeppe @fchapoton @tscrim @jhpalmieri @seblabbe

Component: build

Author: Tobias Diez

Branch/Commit: a5eb21d

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/31080

[sagetrac-git]

Changed commit from c4a802d to 5e4f607

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

5e4f607

Change import exception to print message

[mkoeppe]

comment:3

#22752 was not merged

[mkoeppe]

comment:4

Should this not use warning.warn?

[tobiasdiez]

comment:5

Replying to @mkoeppe:

#22752 was not merged

Ok, it was in 8aac18a. No idea which ticket this corresponds to.

[tobiasdiez]

comment:6

Replying to @mkoeppe:

Should this not use warning.warn?

Not sure, the other code in that file also used simple print statements.

[mkoeppe]

comment:7

Replying to @tobiasdiez:

Replying to @mkoeppe:

#22752 was not merged

Ok, it was in 8aac18a. No idea which ticket this corresponds to.

git trac find thinks it's #22755

[mkoeppe]

Description changed:

--- 
+++ 
@@ -1 +1,3 @@
-In #22752 it was introduced that when a lazy import is used during startup, then an RuntimeException is thrown. This leads to problems if you want to use code with lazy imports in a library mode (e.g. in standalone tests or python scripts). To support these use cases, I've degraded the exception to a print statement. 
+Since #22755, when `lazy_import` is used during startup, a runtime exception is thrown. This leads to problems if you want to use code with lazy imports in a library mode (e.g. in standalone tests or python scripts). 
+
+To support these use cases, this ticket replaces the exception to a `print` (which matches other warnings printed by the same code). 

[mkoeppe]

Reviewer: Matthias Koeppe

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1 and set ticket back to needs_review. New commits:

a5eb21d

Fix doctest