How To Call A Function With Proper 'Arguments'

Question

I have a function that takes 2 returned variables from another function to write them with a little bit more padding text to an external text file.

The code that I am using to write to the text file is below but it is being called automatically at runtime with the if statement at the bottom of the program

def function1()
# Some code

def function2()
# Some code
return startNode
return endNode

def function3(var)
# Some code
return differentVariable

def createFile(startNode, endNode):
    outputFile = open('filename.txt','w')                   # Create and open text file
    start = chr(startNode +65)                              # Converts the int to its respective Char
    end = chr(endNode +65)                                  # Converts the int to its respective Char
    outputFile.write('Route Start Node: ' + start + '\n')   # e.g Route Start Node: B
    outputFile.write('Route end node: ' +  end + '\n')      # e.g Route End Node: F
    outputFile.write('Route: ' + Path + '\n')               # e.g Path: B,A,D,F
    outputFile.write('Total distance: ' + Distance)         # e.g Total Distance: 4
    outputFile.close                                        # Close file


if __name__ == "__main__":
    function1()
    function3(function2())
    createFile( # Don't Know What Goes Here  )

At the moment I am only able to run this function by manually calling it and entering createFile(1,5) where the 1 is the startNode value and the 5 is the endNode value

But if I am to put createFile(startNode, endNode) in the if statement to call the function, it tells me NameError: name 'startNode' is not defined and then it would obviously give me the same error for endNode too

How do I call that function properly without having to enter the values manually because they can change depending on what the startNode and endNode values are at the start of the program?

Answer 1

You can't return two variables as you've done in your example of function2 . Execution will exit the function at the first return value, and never make it to the second. Instead, you need to return a tuple:

def function2():
    # set the values of startNode and endNode here
    # e.g.
    startNode = 1
    endNode = 5
    return (startNode, endNode)

Then when you call function2 , do as Ade described:

if __name__ == "__main__":
    startNode, endNode = function2()
    createFile(startNode, endNode)

Answer 2

But if I am to put createFile(startNode, endNode) in the if statement to call the function, it tells me NameError: name 'startNode' is not defined

Obviously, because all that is being looked at at that point is this:

if __name__ == "__main__":
    function1()
    function3(function2())
    createFile(startNode, endNode)

So if you want to make that last call succeed, you need to define those variables somewhere.

I am guessing that those function calls before are used to initialize the values in some way. You probably “set” startNode and endNode in them some how, but that won't work, as variables inside functions are usually local. So what you want to do is return the values from the functions and save them instead:

if __name__ == "__main__":
    startNode = function1()
    endNode = function3(function2())
    createFile(startNode, endNode)

And the functions should look like this:

def function1 ():
    # some computations
    return startNode

def function3 (param):
    # more computations
    return endNode

Answer 3

You should assign the startNode and endNode to some values.

If they are return by the 2 previous functions:

if __name__ == "__main__":
    startNode = function1()
    endNode = function3(function2())
    createFile(startNode, endNode)