Let's break down why you're hitting this error and fix it step by step:

Root Cause #

The error stems from Python's variable scoping rules. In your identify function, you have lines that assign values to Id (Id = str(b) and Id = "Unknown"). When Python sees an assignment to a variable inside a function, it automatically treats that variable as a local variable for the entire function scope.

But you try to check if(Id == a and conf<65) before assigning any value to the local Id—hence the error: you're referencing a local variable that hasn't been initialized yet.

Solution 1: Use Global Variables #

Since Id and conf are defined outside the identify function, you need to explicitly tell Python you want to use the global versions of these variables inside the function. Add a global declaration at the start of the function:

def identify(number):
    global Id, conf  # Declare we're using the global variables
    sht = gc.open("Test")
    wks3 = sht.worksheet("NAMES")
    b = wks3.acell('B'+str(number)).value
    a = wks3.acell('A'+str(number)).value
    if(Id == a and conf<65):
        print(Id, conf)
        Id = str(b)
        Time = time.ctime()
        hour(number)
    elif(conf>64):
        print(conf)
        Id = "Unknown"

Also, fix the syntax error in your prediction line—you're missing a closing parenthesis:

Id, conf = recognizer.predict(gray[y:y+h,x:x+w])  # Added closing )

Solution 2: Pass Variables as Parameters (Better Practice) #

While global variables work, it's cleaner to avoid them by passing Id and conf as arguments to the identify function. This makes your code more modular and easier to debug:

def identify(number, current_id, current_conf):
    sht = gc.open("Test")
    wks3 = sht.worksheet("NAMES")
    b = wks3.acell('B'+str(number)).value
    a = wks3.acell('A'+str(number)).value
    updated_id = current_id
    if(current_id == a and current_conf < 65):
        print(current_id, current_conf)
        updated_id = str(b)
        Time = time.ctime()
        hour(number)
    elif(current_conf > 64):
        print(current_conf)
        updated_id = "Unknown"
    return updated_id

# Call the function like this:
Id, conf = recognizer.predict(gray[y:y+h,x:x+w])
for m in range(2,100):
    Id = identify(m, Id, conf)

This approach avoids relying on global state, which is generally considered better practice for maintainable code.

内容的提问来源于stack exchange，提问作者Michael O' Driscoll