函数之间的全局变量总是 = 无 python

Question

I have this code:

last_price=None

def trade(price,last_price=last_price)
  if last_price == None:
    print("last_price=None!")
    last_price = price
    #do something else

while True:
  price= get_price_function()
  trade(price)

Buy I have the problem - last_price is always None(it seems that it's outside the scope of function, so how to use global variable last_price , so it is not always none.

Answer 1

In order to access a global variable inside a function, declare it with global keyword.

Change your trade function to:

def trade(price)
  global last_price
  if last_price == None:
    print("last_price=None!")
    last_price = price
    #do something else