Functions and Modules in Python — Foundations

3 min readJan 23, 2021

usecase

The concern is documenting the most basic use of concepts like MODULARITY, REUSABLE FUNCTIONS & MODULES in python with the use of VSCode and Python Repl. Notes under the awesome Core Python: Getting Started @ Pluralsight

1. shell (powershell core)

install the Python extension for VSCode
to run the existing python file in REPL just use Run Python File in Terminal from VSCode
Get Started Tutorial for Python in Visual Studio Code
or, from the shell run python <filename.py>

2. code without functions: execute now!

you can import the .py file and run — without function block; immediatelly
start REPL with python
use import <filename> — without .py
the code executes immediately

# NO FUNCTION
from urllib.request import urlopenstory = urlopen("http://sixty-north.com/c/t.txt")
story_words = []
for line in story:
    line_words = line.decode("utf-8").split()
    print(line)
    for word in line_words:
        story_words.append(word)
story.close()for word in story_words:
    print(word)

3. function — run when qualified

usually, you don’t want to run the code immediately
wrap the code in a function
functions, therefore, give you not only re-usability (not repeating yourself) but also give you control as to when your code is executed
the def keyword defines functions
return returns a value
the return is explicit — and it signals that the function is a query
without return, the function is a command that has a side-effect
remember command/query separation

#WORDS.PY WITH A FUNCTION
from urllib.request import urlopendef fetchwords():
    story = urlopen("http://sixty-north.com/c/t.txt")
    story_words = []
    for line in story:
        line_words = line.decode("utf-8").split()
        print(line)
        for word in line_words:
            story_words.append(word)
    story.close()    for word in story_words:
        print(word)

4. early exit

you can use return keyword for an early exit
no return value is required

5. None is returned by both implicit return and return without return val

there is no value returned by a function without a return statement (difference to other languages)
this is aphorism 2 from the Zen of Python

explicit is better than implicit

implicit return, i.e. a return at the end of the function, returns None
running an early exit with Return also returns None

6. REPL/Code import syntax1 — qualified name

run import words → words.fetchwords() to run the function in REPL

7. REPL/Code import syntax2 — unqualified name

run from words import fetchwords → fetchwords()

8. import or execute pattern: name & main

specially named binding allowing us to detect whether a module is run as a script or imported into another module
when you add print(__name__) at the end of the module, the module name is printed during the first import
if (and only if) the function with print(__name__) in the module is called from the shell with python words.py the shell return

▶ python words.py
__main__

now you can modify the behavior so that the module is executed from shell but loaded from REPL

from urllib.request import urlopendef fetchwords():
    story = urlopen("http://sixty-north.com/c/t.txt")
    story_words = []
    for line in story:
        line_words = line.decode("utf-8").split()
        print(line)
        for word in line_words:
            story_words.append(word)
    story.close()    for word in story_words:
        print(word)if __name__ == "__main__":
    fetchwords()