Calling python functions without running from the editor

If you want to use functions defined in a particular file in Python you need to "import" that file first. This is similar to running the code in that file. Matlab doesn't require you to do this because it searches for files with a matching name and automagically reads in the code for you.

For example,

myFunction.py is a file containing

def myAdd(a, b):
    return a + b

In order to access this function from the Python command line or another file I would type

from myFunction import myAdd

And then during this session I can type

myAdd(1, 2)

There are a couple of ways of using import, see here.

You need to a check for __main__ to your python script

def myFunction():
  pass

if __name__ == "__main__":
  myFunction()

then you can run your script from terminal like this

python myscript.py

Also if your function is in another file you need to import it

from myFunctions import myFunction
myFunction()

Python doesn't have MATLAB's "one function per file" limitation. You can have as many functions as you want in a given file, and all of them can be accessed from the command line or from other functions.

Python also doesn't follow MATLAB's practice of always automatically making every function it can find usable all the time, which tends to lead to function name collisions (two functions with the same name).

Instead, Python uses the concept of a "module". A module is just a file (your .py file). That file can have zero or more functions, zero or more variables, and zero or more classes. When you want to use something from that file, you just import it.

So say you have a file 'mystuff.py':

X = 1
Y = 2

def myfunc1(a, b):
   do_something

def myfunc2(c, d):
   do_something

And you want to use it, you can just type import mystuff. You can then access any of the variables or functions in mystuff. To call myfunc2, you can just do mystuff.myfunc2(z, w).

What basically happens is that when you type import mystuff, it just executes the code in the file, and makes all the variables that result available from mystuff.<varname>, where <varname> is the name of the variable. Unlike in MATLAB, Python functions are treated like any other variable, so they can be accessed just like any other variable. The same is true with classes.

There are other ways to import, too, such as from mystuff import myfunc.

You run python programs by running them with

python program.py