Those other things that are good to know

• == tests "value equality"
• is tests "identity equality"

The Python Execution Model

• def is actually a statement
  • when executed in sequence with other top-level model scope code, causes code within function to be bound to name of function
• top-level functions are defined when a module is imported or run
  • when modules are imported or run, all top-level statements are run, which is what results in function(s) within module namespace being defined

Module, Script, or Program

• Python module: convenient import with API
• Python script: convenient execution from from command line
• Python program: perhaps composed of many modules(?)

It is strongly suggested that scripts are importable as modules and that modules can be executable.

For this reason, most modules adhere to form of defining one or more importable functions, followed by a postscript to facilitate execution as a script

Command Line Arguments

import sys
from urllib.request import urlopen

# 'http://sixty-north.com/c/t.txt'


def fetch_words(url):
    story = urlopen(url)
    story_words = []

    for line in story:
        line_words = line.decode('utf8').split()
        for word in line_words:
            story_words.append(word)
    story.close()
    return story_words


def print_items(items):
    for item in items:
        print(item)


def main(url):
    words = fetch_words(url)
    print_items(words)


if __name__ == '__main__':
    main(sys.argv[1])

• more import examples

# importing multiple objects from module
from cli_args_words import (fetch_words, print_words)

# import everything from module
from cli_args_words import *

• access of command-line arguments through attribute of sys module called argv (a list of strings)
• after first refactor, can run from shell with:

$ python /_demos/story_words/cli_args_words.py http://sixty-north.com/c/t.txt

• however, can no longer be run from REPL env, since url in main() is unlikely to get any value from sys.argv[1]

• 2nd refactor fixes this issue to make main() accept the url param

• Additional inspiration:

  • arg parse module
  • doc opt module (third-party)

☯️ Moment of Zen ☯️ "Sparse is better than dense" Two between functions That is the number of lines PEP8 recommends

Docstrings

• literal strings which document functions, modules, and classes

• must be FIRST statement in blocks for these constructs

• convention for docstrings is documented in PEP257, though not widely adopted

• Sphinx: tool for creating HTML documentation from Python docstrings

• form from Google's Python Style Guide is used in this course

Shebang

#!/usr/bin/env python

• mark script as executable

$ chmod +x /path/to/script.py