Multithreading in Python , previous and actual data in dictionary are the same

I'm implementing a multithreading in Python and I have an issue with the data. Basically (simplifying the code)first thread is collecting data from external source each 0.5s. The code is as follow:

dataRef = {}
data_lock = threading.Lock()

def readData():
  global dataRef
  dataRefNew = {}
  while True:
      dataRefsValues = simulate_external_data_source()
      with data_lock:
         dataRef = dataRefsValues
      sleep(0.5)

And another thread which checks if previous data and active data are the same or changed

def eventCheck():
    global dataRef
    dataRefPrevious = {}
    dataRefActive = {}
    
    while True:
        with data_lock:
            if bool(dataRefPrevious) == True:
                dataRefActive = dataRef
                print('dataRefPrevious', dataRefPrevious,"\n")
                print('dataRefActive', dataRefActive, "\n")
                dataRefPrevious = dataRefActive
            else:
                dataRefPrevious = dataRef
    sleep(1)

The problem I got is that during the looping dataRefPrevious is always the same as dataRefActive, why?

I potentially found a issue but have not a clear explanation why...

I tested a function:

def eventCheck():
   global dataRef
   dataRefPrevious = {}
   dataRefActive = {}
   i = 0
   while True:
        i +=1  
        print("\n Iteration: ", i)
        with data_lock:
            dataRefActive = dataRef
            print('dataRefActive  : ', dataRefActive)
            print('dataRefPrevious: ', dataRefPrevious)

        if dataRefPrevious:
            print('dataRefPrevious in if statment: ', dataRefPrevious)
            dataRefPrevious = dataRefActive
        else:
            dataRefPrevious = dataRefActive
        sleep(1)

And what I get is:

 Iteration:  1
dataRefActive  :  {'flaps': 0.0}
dataRefPrevious:  {}

 Iteration:  2
dataRefActive  :  {'flaps': 0.0}
dataRefPrevious:  {'flaps': 0.0}
dataRefPrevious in if statment:  {'flaps': 0.0}

 Iteration:  3
dataRefActive  :  {'flaps': 1.2505772113800049}
dataRefPrevious:  {'flaps': 1.2505772113800049}
dataRefPrevious in if statment:  {'flaps': 1.2505772113800049}

 Iteration:  4
dataRefActive  :  {'flaps': 4.265423774719238}
dataRefPrevious:  {'flaps': 4.265423774719238}
dataRefPrevious in if statment:  {'flaps': 4.265423774719238}

 Iteration:  5
dataRefActive  :  {'flaps': 7.3065643310546875}
dataRefPrevious:  {'flaps': 7.3065643310546875}
dataRefPrevious in if statment:  {'flaps': 7.3065643310546875}

However when I repalce the the following line in the code:

dataRefPrevious = dataRefActive

to:

dataRefPrevious.update(dataRefActive)

I'm getting correct values as follow (previous different than active)

Iteration:  1
dataRefActive  :  {'flaps': 0.0}
dataRefPrevious:  {}

 Iteration:  2
dataRefActive  :  {'flaps': 0.0}
dataRefPrevious:  {'flaps': 0.0}
dataRefPrevious in if statment:  {'flaps': 0.0}

 Iteration:  3
dataRefActive  :  {'flaps': 0.20687073469161987}
dataRefPrevious:  {'flaps': 0.0}
dataRefPrevious in if statment:  {'flaps': 0.0}

 Iteration:  4
dataRefActive  :  {'flaps': 3.2361574172973633}
dataRefPrevious:  {'flaps': 0.20687073469161987}
dataRefPrevious in if statment:  {'flaps': 0.20687073469161987}

 Iteration:  5
dataRefActive  :  {'flaps': 6.276290416717529}
dataRefPrevious:  {'flaps': 3.2361574172973633}
dataRefPrevious in if statment:  {'flaps': 3.2361574172973633}

 Iteration:  6
dataRefActive  :  {'flaps': 9.321335792541504}
dataRefPrevious:  {'flaps': 6.276290416717529}
dataRefPrevious in if statment:  {'flaps': 6.276290416717529}

I'm thinking that = makes a ref of dict dataRefPrevious to dataRefActive dict while .update() changes the variable itself.