在更高范围内访问python类属性

Question

Still learning Python, rookie question here. I'm building a simple tkinter GUI that loads JSON data and then allows the user to select loaded data for plotting. Here's a description of my architecture and issue:

1) In the GUI, I have a load button that calls a function, LoadData, to open a directory containing multiple JSON txt files

2) LoadData checks to see if a certain file name exists, 'AutoPilot.txt', and if it does, another function, LoadAutopilotData, is called

3) LoadAutopilotData creates an instance of the Data class and populates it with the JSON data

After the functions are complete, I want to access the instance of the Data class I created in the inner scope (APtime), but I can't seem to do that.

File 1 snippet:

loadBtn = Button(toolbar, image=useImg1, command=LoadData)

File 2 snippet:

def LoadData() :

    # Get data Path from the User
    path = askdirectory()

    # Go to that directory
    os.chdir(path)

    # Check directory to see if AutoPilot.log is available
    try:
        Autopilot = open("AutoPilot.txt")
        Load_Autopilot = True
    except:
        Load_Autopilot = False

    # If Autopilot data exists, load it and populate the listbox
    if Load_Autopilot == True:
        LoadAutopilotData()
        print(APtime.val)

File 3 snippet:

def LoadAutopilotData() :

    filedata = open( 'AutoPilot.txt' )

    if len( sys.argv) >= 2:
        controller = sys.argv[1]

    APtime = Data("Time", [], "sec")

where File3 continues on to populate an instance of the Data class. The problem I'm having is that I can only access APtime in File3, and not in the 'higher' level functions. Any help is greatly appreciated. Thanks!

Answer 1

What you need to do is return a value to the calling function. You can look at the tutorial section on Defining functions on the Python website to have a little more detail about that.

So if we don't change your code too much this could loook like that:

Solution 1: File 2 snippet

def LoadData() :

    # Get data Path from the User
    path = askdirectory()

    # Go to that directory
    os.chdir(path)

    # Check directory to see if AutoPilot.log is available
    try:
        Autopilot = open("AutoPilot.txt")
        Load_Autopilot = True
    except:
        Load_Autopilot = False

    # If Autopilot data exists, load it and populate the listbox
    if Load_Autopilot == True:
        APtime = LoadAutopilotData()
        print(APtime.val)

Solution 1: File 3 snippet

def LoadAutopilotData() :

    filedata = open( 'AutoPilot.txt' )

    if len( sys.argv) >= 2:
        controller = sys.argv[1]

    APtime_result = Data("Time", [], "sec")

    return APtime_result

• You should see that the function LoadData() assign the value returned by the function LoadAutopilotData() to the APtime variable (the line APtime = LoadAutopilotData() )
• After the function LoadAutopilotData() process its data, it uses the statement return APtime_result to make that value available to the calling function.

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But there are some improvement that could be done in your code. The only one I will mention is that you should read what is in the Standard Library because it could save you some work. For example, to check if a file exists, there's a function that already exists for that.

So your File 2 snippet could look like that:

import os.path

def LoadData() :

    # Get data Path from the User
    path = askdirectory()

    Load_Autopilot = os.path.exists(path)

    # If Autopilot data exists, load it and populate the listbox
    if Load_Autopilot:
        APtime = LoadAutopilotData()
        print(APtime.val)