Does python debugger (pdb) keep fiddling with global variables within the function scope?

I was playing with the following code to check the behavior of pdb in vscode.
Bring the breakpoint to the print ("start") on the second line from the bottom and start
I will proceed with step into .
After a=100, when the cursor comes to print(a),
In GUI operation, if a=1000, the number will be updated, but it will be returned to 100 immediately. (Not updated?)
You cannot update the global variable from DEBUG CONSOLE in the first place.
In pdb, is there a way to enter or update global variables using DEBUG CONSOLE, etc. within a function?

defmain():
    global a
    a = 100
    print(a)
    func1()


def func1():
    b = 200
    print(b)
    func2()

def func2():    
    c=300
    print(c)
    func3()

def func3():
    d = 400
    print(d)

print ("start")
main()