Apply #18731 again

[jdemeyer]

Some modifications made in #18731 disappeared in #18748. These should be applied again.

CC: @jhpalmieri

Component: build

Author: Jeroen Demeyer

Branch/Commit: 9258278

Reviewer: John Palmieri

Issue created by migration from https://trac.sagemath.org/ticket/19349

[jdemeyer]

Branch: u/jdemeyer/apply__18731_again

[jdemeyer]

New commits:

5a0c4b0

Better error handling in sage-download-file

[jdemeyer]

Commit: 5a0c4b0

[vbraun]

comment:5

Magic string anti-pattern: https://en.wikipedia.org/wiki/Magic_string

[sagetrac-git]

Changed commit from 5a0c4b0 to 088fdef

[sagetrac-git]

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

088fdef

Avoid magic string

[vbraun]

comment:7

Its still a magic string. If somebody were to change the magic value to

fastest_mirror = "http:// fastest mirror"

then the program doesn't work any more. Fragile and difficult to follow.

[sagetrac-git]

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

9258278

Avoid magic string

[sagetrac-git]

Changed commit from 088fdef to 9258278

[jdemeyer]

comment:9

Better like this?

[vbraun]

comment:10

The usual pattern is to throw exceptions that have the error message and catch them at the outermost level. Without relying on any local variable being in scope at the exception handler. But its an improvement, at least.

[vbraun]

Changed branch from u/jdemeyer/apply__18731_again to 9258278