每次迭代函数时都要写到新行？

Question

I'm just having a little trouble with text files and how I would write to a new line to create a list every time a function is called.

if speedCarMph > 60:
        f = open('Camera Output.txt', 'r+')
        f.write("{} was travelling at {}MPH at {} and has broken the law".format(licensePlate, speedCarMph, camInput2) + "\n")
        f.write("-----------------------------------------------------------------------------------------------------------")
        f.close()
        DeltaTimeGen()
    else:
        DeltaTimeGen()

I would like to write to a new line of the text file everytime this is passed and the function is called.

Answer 1

Use a to append, if you have a loop you should also open the file outside it:

with open('Camera Output.txt', 'a') as f: # with closes your file
    if speedCarMph > 60:              
            f.write("{} was travelling at {}MPH at {} and has broken the law".format(licensePlate, speedCarMph, camInput2) + "\n")
            f.write("-----------------------------------------------------------------------------------------------------------\n")
    DeltaTimeGen() # if/else is redundant

r+ opens for reading and writing so the pointer is going to be at the start of the file when you open it therefore will write to the first line not append to it.

If the function is repeatedly calling itself you may be better off using a while loop.

with  open('Camera Output.txt', 'a') as f:
    while True:
        # rest of code 
        if speedCarMph > 60:
                f.write("{} was travelling at {}MPH at {} and has broken the law".format(licensePlate, speedCarMph, camInput2) + "\n")
                f.write("-----------------------------------------------------------------------------------------------------------")

Maybe adding a time.sleep in between checks.

Answer 2

You can open the file only once and close it when you're program exits. Just add a "\\n" to the end of your f.write line. If you need the file to be flushed (so that output appears immediately) you can specify zero buffering:

bufsize = 0
f = open('Camera Output.txt', 'r+', bufsize)

if speedCarMph > 60:
        f.write("{} was travelling at {}MPH at {} and has broken the law".format(licensePlate, speedCarMph, camInput2) + "\n")
        f.write("-----------------------------------------------------------------------------------------------------------\n")
        DeltaTimeGen()
    else:
        DeltaTimeGen()

f.close()