Q:

TypeError: send_data() missing 1 required positional argument: 'event'

Here is code
from tkinter import *
from tkinter.ttk import *
from tkinter import messagebox
import socket
import threading

s = socket.socket(socket. AF_INET, socket. SOCK_STREAM)

class Chat(object):

    def __init__(self):

        self. IP = ''
        self. PORT = 9999
        self.conn()

        window = Tk()
        window.title("3406")
        frame = Frame(window).pack()

        ws = window.winfo_screenwidth()
        hs = window.winfo_screenheight()
        x = int((ws / 2) - (300 / 2))
        y = int((hs / 2) - (300 / 2))
        window.geometry('{}x{}+{}+{}'.format(500, 350, x, y))
        window.resizable(0, 0)

        self.text = Text(frame,yscrollcommand=True)
        self.text.pack(anchor=W)
        self.entry = Entry(frame)
        self.entry.pack(side=LEFT, expand=YES, fill=X, anchor=W)
        self.entry.focus_force()             
        self.entry.bind("<Return>", self.send_data)

        #self.button = Button(frame, text="发送", command=self.send_data).pack(side=RIGHT, anchor=W)

        self.send_threading = threading. Thread(target=self.send_data)
        self.recive_threading = threading. Thread(target=self.recive_data)
        self.send_threading.setDaemon(True)
        self.recive_threading.setDaemon(True) 
        self.send_threading.start()
        self.recive_threading.start()

        window.mainloop()

    def conn(self):
        try:
            s.connect((self. IP, self. PORT))
        except:
            messagebox.showerror("Error", "Error the client is not open")

    def recive_data(self):
        while True:
            data = s.recv(1024)
            data = data.decode("utf-8")
            print(data)
            self.text.insert(END,data + "\n")

    def send_data(self,event):
        self.event=event
        try:
            data = self.entry.get()
            # print(data)
            if data is not None:
                s.send(data.encode("utf-8"))
                self.entry.delete(0, 'end')

        except:
            messagebox.showerror("Error", "Error the client is not open!") 
            exit(1)

if __name__ == '__main__':
    Chat()

my error is TypeError: send_data() missing 1 required positional argument: 'event'
 i am new so I can't figure out what I do wrong.  I don't know what that means. 

A:

There are probably many things wrong with your code and it will not do what you expect it to do.  This error, however, means exactly what it says.  send_data expects a parameter but you are not sending it one.  
self.send_threading = threading. Thread(target=self.send_data)

calls your send_data function without any parameters.  The function expects something in event but does not receive a parameter and raises an exception. 