Empty symbol_formatting_map

[kwadwobro1]

async def start_websocket(self):
print_([self.symbol_formatting_map])
uri = "wss://stream.binance.com:9443/stream?streams=" + '/'.join(
list(self.symbol_formatting_map))
print_([uri])

The output of the code above is

{}
wss://stream.binance.com:9443/stream?streams=

But in _init

self.symbol_formatting_map = {
s.replace('/', '').lower() + f'@Depth{self.depth_levels}': s for s in self.symbols
}

Why is self.symbols empty