Smooth Keyboard Press

I have this code to move my player…

function keyboardPress (key:KeyboardEvent):void{
    if (key.keyCode == Keyboard.LEFT){
        player.x -= 4;

…however, when the left key is pressed, the player jumps left once, pauses, then continues to move left.

In AS2,

if (Key.isDown(Key.LEFT)){player.x -= 4;}

provided for a much smoother movement.

So, what is the code equivalent in AS3 of the code from AS2 above? Or, in other words, how do I write a smooth keyboard movement code for AS3?