global-var.md

title
Global variables

The variables we declare inside a function are local to the function. It cannot be used by another function. However, a global variable once declared/set, it can be accessed by other functions. Here is an example: we will write a program (equivalent of MATLAB tic and toc commands) that is combination of two functions: tic which starts the timer and toc which stops the timer and prints the time interval between calling tic and toc functions.

First let us write the tic program and set the current time as a global variable:

def tic():
    import time

    global tictoc_start_time
    tictoc_start_time = time.time()

    return

toc program that prints the elapsed time:

def toc():
    import time

    if "tictoc_start_time" in globals():
        elapsed_time = time.time() - tictoc_start_time
        print("Elapsed time =", elapsed_time, "sec.")
    else:
        print("First run the tic() program, start time is not set.")
        elapsed_time = 0.0

    return elapsed_time

Of course, you should introduce global variables with care, as they might conflict with other parts of the program.