Close the windows???

As Réka says: mosquito nets, sticky paper. Sprays and scents are not really good for anyone, even if they work. Also, when flies do get in: Spray/club them on sight, so they won't populate.

At night, you can use red light bulbs instead of normal light bulbs, as flying insects, in general, can't see red light and won't be attracted (yellow, on the other hand.. and TV screens).

There's an 'anti-bug store' at Place des Eaux-Vives, at the side of Terrassiere. They should be able to help you.

But if you stay next to a farm all those things might not help, but you can still try the "anti-bug store" at Place des Eaux-Vives. Well mosquito nets are also good but be warned summer is here and more flies will come. Sorry about that.

Try filling water in transparent plastic bags & hanging them near the windows & balconies.  Apparently, this creates an illusion of water bodies/spiderwebs & flies stop entering.

Hope this helps.

Hey Cassie, Had same problem, its coz we're in the country.

Head down to Leroy merlin in Thoiry. I got Nets, for about 5 euro each that you stick onto the window. They are see through but keep the flies out.

Kevin

The name of the Eaux Vives store is L'araignée rouge.  Depends what type of fly you have.  Have had only one or two house flies this year despite windows always open but have had problems with small flies which like rice, sugar flour and dried fruits. 

Got a sticky paper from l'A. which worked but only real way to tackle problem is to put such foods in screw top containers as they make their way in to unopended packets of sugar and can eat through plastic

get a chameleon?

And when you do kill all those poor innocent flies who have as much a right to live as you, here's how you can turn your evil deed into ART . . . .

and more inspiration . . .

Just be thankful you don't live in Aussie!