I've found a few papers/posts on the history of streetlights and electricity in Paris, but I can't seem to find an answer to that direct question.
The answer seems to be : both, depending on where you were. There were a million Parisians connected to electricity by 1920, yet the last gas lights were working until the 1960's ( and some seem to be still in place, although unsupplied) . Brassai could photograph a lamp-lighter in the 1933, and Saint-Exupery could include a lamplighter in his classic The Little Prince, in 1943, set on a small planet that's spinning so quickly he constantly is lighting and extinguishing his one lamp.
But bigger streets, boulevards, seem to have gotten electrified. In 1907, George Dary would note ( this is merely Google Translate) :
As of April 30, 1891, the City granted a ten-year concession during which it paid 57 cents per hour and per 15 amp lamp and 40 cents per 10 amp lamp. This concession was renewed in 1901 for the same period of time. Lighting the boulevards represents an annual expenditure of 348,000 francs instead of 121,000 francs, the price of gas. But it should be noted that the light is at least ten times more intense. Since 1897, the left bank has had a sector and finally enjoys the benefits of civilization and… electric lighting.....This is why arc lamps reign supreme on boulevards and main roads, in stations, on the peristyle of theaters, in factories and workshops