Hi wol6 . . here is a same view picture taken in 1910. Definitely earlier than your picture but if you look on the left top there ins a white banner which reads Photographie Helios - this appears on both pictures. Also the trams are a little older than on your picture but they follow the same route.
I'd go for 1920's too. By the 30's cars had already begun to be a little less bulky and boxy looking- of course they could always be older cars still there in the 30's but I reckon if you work on about 1927- 1935 as a timescale you won't be far wrong.
Thanks everyone - with your help I eventually found the exact scene and the same card for sale. It is a 1937 card. It is only worth a couple of pounds - but one day I will find something valuable. Pity it doesn't belong to me.