myList = [[1,2,3],[4,5,6],[7,8,9]]

#Quick answer
print([ele[0] for ele in myList])   #Prints [1, 4, 7]

#Other variations
print([[ele[0]] for ele in myList]) #Prints [[1], [4], [7]]
print([[ele[0] for ele in myList]]) #Prints [[1, 4, 7]]