[toyg]

The European Arrest Warrant effectively supersedes any constitutional right to non-extradition: "EU countries can no longer refuse to surrender [to other EU members] their own nationals, unless they take over the execution of the prison sentence against the wanted person" [1]. EU members with extradition impediments like France are left with a right to get back prisoners after conviction, to spend the punishment in their own country. There are exceptions and rules but "constitution says no" is not one of them (or at least I could not find it even in the proper text of the Decision [2], and is not mentioned in any note on the matter).

This said, a "bad" EU members might well choose to extradite further, once a prisoner is obtained from France. I expect this would trigger appeals at the ECJ and possibly repercussions for the "bad" country, but in the meantime the prisoner might well be gone. I also don't know what the "punishment" would be for a country that refused to execute a valid EAW. I guess this sort of thing is left to ECJ judges.

[1] https://ec.europa.eu/info/law/cross-border-cases/judicial-co...

[2] https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CEL...

[retrac]

Such laws do not supersede the constitutions of its sovereign member nations. If a member nation's constitution requires something that would place them in violation a treaty agreement, then it would have to fix its constitution or be in violation. The treaty itself doesn't change municipal law, though. (Unless it's a country where it does, anyway. But France is not one of them.)

> unless they take over the execution of the prison sentence against the wanted person

Yes, that bit. France still cannot extradite its citizens, but it can meet its obligations to its partners by prosecuting and incarcerating someone within France.