Game progress crashs

[QuBuZhou]

Hi, I want to make a project which called 'Your first 2d game' in the godot api documentation with py4godot instead of gdscript. When I try to press the button to make sprite move, the game window crashs. here is the code:
`python
from py4godot.classes.AnimatedSprite2D.AnimatedSprite2D import AnimatedSprite2D
from py4godot.classes.Input.Input import Input
from py4godot.classes.Node2D.Node2D import Node2D

from py4godot.methods import private
from py4godot.signals import signal, SignalArg
from py4godot.classes import gdclass
from py4godot.classes.core import Vector3, Vector2, StringName, NodePath
from py4godot.classes.Area2D.Area2D import Area2D

@gdclass
class Player(Area2D):
node_path: NodePath
speed: int = 400
str_up: StringName
str_down: StringName
str_left: StringName
str_right: StringName

def _ready(self) -> None:
	self.screen_size: Vector2 = self.get_viewport_rect().size
	self.velocity: Vector2 = Vector2.new3(0, 0)
	self.sprite = AnimatedSprite2D.cast(self.get_node(self.node_path))

# put initialization code here
def _process(self, delta: float) -> None:
	if Input.get_instance().is_action_pressed(self.str_right):
		self.velocity.x += 1
	if Input.get_instance().is_action_pressed(self.str_left):
		self.velocity.x -= 1
	if Input.get_instance().is_action_pressed(self.str_up):
		self.velocity.y += 1
	if Input.get_instance().is_action_pressed(self.str_down):
		self.velocity.y -= 1

	if self.velocity.length() > 0:
		self.velocity = self.velocity.normalized() * self.speed

		self.sprite.play()
	else:
		self.sprite.stop()

	self.position += self.velocity * delta
	self.position.clamp(Vector2.new3(0, 0), self.screen_size)

	if self.velocity.x != 0:
		self.sprite.animation = "walk"
		self.sprite.flip_v = False
		self.sprite.flip_h = self.velocity.x < 0
	elif self.velocity.y != 0:
		self.sprite.animation = "up"
		self.sprite.flip_v = self.velocity.y > 0

`
Is there anything wrong in the code? if yes, please point out; if not, please fix the bug.

[QuBuZhou]

So after a few time I finish a small project, but there's no mistake, perhaps I gone wrong on the other hand?