Marrying a tunisian policeman

While not serving the government's herself, my ex-wife comes from a family of people that work in the Ministry of Interior and I can tell you that while marrying a foreigner can certainly disqualify a new applicant who is interested in joining the Tunisian police force, it is not categorically forbidden for someone who is a police officer to marry a foreigner. A bigger issue would be the fact that once you become a police officer in this country, it is usually impossible, or rather very, very difficult to quit and many people move abroad for a few years and then come back while still retaining their warrant card (called a carte dé service in French) and thus legally being considered police officers, so be careful of any scams in which your future partner to be might advise you to move abroad: because he will still retain his police "privileges" in the country and it is impossible to just give up on the job and get married because he will not be able to marry you in the municipality without prior permission from his employers.

Note that I began my post by mentioning that the woman is my ex-wife: people who have worked in the police force come from a very specific socioeconomic background, that no sane person who values his  or her mental health would like to be around so I would advise you to abandon this prospect of a relationship. Find yourself a university graduate with similar interests to yourself.