What is the meaning of "for" in the bold sentence? Is it an idiomatic use?
He told Hagrid about the pale boy in Madam Malkin's. "--and he said people from Muggle families shouldn't even be allowed in." "Yer not from a Muggle family. If he'd known who yeh were -- he's grown up knowin' yer name if his parents are wizardin' folk. You saw what everyone in the Leaky Cauldron was like when they saw yeh. Anyway, what does he know about it, some o' the best I ever saw were the only ones with magic in 'em in a long line o' Muggles -- look at yer mum! Look what she had fer a sister!"