overview of python's stdlib

Goal

• walk through quite big python's^* stdlib with short stops on more interesting parts of it
• no need to reinvent the wheel
• no need for third party dependencies

This is not a comparisson against other programming languages

Built-in types

set

collection of distinct hashable objects

set

              
# check if list is from the same elements
len(set(humongous_list)) == 1

# compare dicts.
# symmetric difference,
# if items are equal - returns empty set
set(foo_dict.items()) ^ set(bar_dict.items())
# there are more operations: subset, superset, union, etc.

# set comprehension
{user.profession for user in users}
# {'administrator', 'engineer', 'manager'}
              
            

Text processing services

string

              
import secrets
import string

# create string with random letters and digits
symbols = string.ascii_letters + string.digits
random_string = ''.join(secrets.choice(symbols) for i in range(50))
print(random_string)
# ugszGgIRBZ9TduZxtpBDyK0Odp6qHyAxDBmBU7s5xpUPGfHAt4
              
            

textwrap

              import textwrap

s = "Lorem ipsum dolor sit amet, consectetur adipiscing elit."
textwrap.wrap(s, width=8)
# ['Lorem',
#  'ipsum',
#  'dolor',
#  'sit',
#  'amet, co',
#  'nsectetu',
#  'r adipis',
#  'cing',
#  'elit.']
textwrap.shorten("Hello  world!", width=10)
# 'Hello [...]'
              
            

Data types

calendar

              
import calendar

calendar.monthrange(2017, 3)
# March starts on wednesday and has 31 days
# (2, 31)
calendar.day_name[calendar.weekday(2017, 3, 15)]
# 'Wednesday'
calendar.HTMLCalendar(2017, 3)
              
            

collections

collections.namedtuple

              
import collections

Point = collections.namedtuple("Point", ["x", "y"])
p = Point(3, 4)

import math

math.sqrt(p.x ** 2 + p.y ** 2)
# 5.0
              
            

collections.defaultdict

              
import collections

s = [('submit', 'create_instance'),
     ('delete', 'notify'),
     ('submit', 'send_email'),
     ('touch', 'scroll'),]
d = collections.defaultdict(list)
for k, v in s:
    d[k].append(v)

sorted(d.items())
# [('delete', ['notify']),
#  ('submit', ['create_instance', 'send_email']),
#  ('touch', ['scroll'])]
              
            

pprint

              
import calendar
import pprint

pprint.pprint(dir(calendar.HTMLCalendar()))
# ['__class__',
#  '__delattr__',
#  '__dict__',
#  '__dir__',
#  ....
#  'firstweekday',
#  'formatday',
#  'formatmonth',
#  ....
#  'yeardayscalendar']
              
            

Numeric and Mathematical modules

statistics

            
import statistics

salaries = [100, 114, 180, 200, 205, 240, 1000]
statistics.mean(salaries)
# 291.2857142857143

statistics.median(salaries)
# 200

statistics.stdev(salaries)
# 316.5147254529739
              
            

Functional programming modules

itertools

itertools.cycle

              
import itertools

c = itertools.cycle('ABC')
next(c)
# 'A'
next(c)
# 'B'
next(c)
# 'C'
next(c)
# 'A'
              
            

itertools.filterfalse

              
import itertools

# leave uneven numbers
ff = itertools.filterfalse(lambda x: x % 2 == 0, range(10))
for i in ff:
    print(i)
# 1
# 3
# 5
# 7
# 9
              
            

itertools.groupby

              
from datetime import datetime as dt
import itertools

# work start and finish log
log = [(dt(2010, 1, 1, 8), 'arrive'),
       (dt(2010, 1, 1, 16), 'leave'),
       (dt(2010, 1, 2, 9), 'arrive'),
       (dt(2010, 1, 2, 16), 'leave')]

g =  itertools.groupby(sorted(log, key=lambda x: x[0].hour),
                       key=lambda x: x[0].hour):
for key, group in g:
    print(key, list(group))
# 8 [(datetime.datetime(2010, 1, 1, 8, 0), 'arrive')]
# 9 [(datetime.datetime(2010, 1, 2, 9, 0), 'arrive')]
# 16 [(datetime.datetime(2010, 1, 1, 16, 0), 'leave'),
#     (datetime.datetime(2010, 1, 2, 16, 0), 'leave')]
              
            

itertools.product

              
import itertools

for i in itertools.product(['a', 'b'], [1, 2]):
     print(i)
# ('a', 1)
# ('a', 2)
# ('b', 1)
# ('b', 2)
              
            

functools

              
import functools

quinary = functools.partial(int, base=5)
quinary('10')
# 5

Engineer = functools.partial(User, profession="engineer")
              
            

File and Directory access

pathlib

              
import pathlib

p = pathlib.Path(__file__)
scripts = p / "scripts"
python_scripts = scripts.glob("*.py")

p.parts()
# ('/', 'opt', 'my_app')
              
            

Data persistence

Data compression and archiving

File formats

configparser

INI like config file parsing

configparser

              
# config.ini
[network]
port = 8080

[secrets]
pub_key = very_secret
priv_key = supah_secret
              
            

configparser

              
import configparser

config = configparser.ConfigParser()
config.read('config.ini')
config['network']['port']
# '8080'
config['network']['port'] = '1337'
with open('config.ini', 'w') as configfile:
    config.write(configfile)
              
            

Cryptographic services

secrets

              
import secrets

secrets.token_urlsafe(nbytes=8)
# 'Ca8rdNzYQmY'
              
            

Internet protocols and support

wsgiref

              # https://docs.python.org/3.6/library/wsgiref.html#examples
from wsgiref.simple_server import make_server

def hello_world_app(environ, start_response):
    status = '200 OK'  # HTTP Status
    headers = [('Content-type', 'text/plain; charset=utf-8')]
    start_response(status, headers)

    # The returned object is going to be printed
    return [b"Hello World"]

with make_server('', 8000, hello_world_app) as httpd:
    print("Serving on port 8000...")

    # Serve until process is killed
    httpd.serve_forever()
              
            

urllib

              
import urllib.request

r = urllib.request.urlopen("http://vilniuspy.lt")
r.status
# 200
              
            

http

              
$ python3 -m http.server
              
            

Frameworks

turtle

            
from turtle import *

color("red", "yellow")
begin_fill()
while True:
    forward(200)
    left(170)
    if abs(pos()) < 1:
        break
end_fill()
done()
              
            

turtle

GUI with Tkinter

tkinter

              
import tkinter as tk

root = tk.Tk()
root.mainloop()
              
            

Dev tools

pydoc

              
$ ls
my_file.py

$ pydoc -w my_file
wrote my_file.html
              
            

doctest

              
# times.py
def times2(number):
    """
    >>> times2(5)
    10
    """
    return number * 2

$ python -m doctest times.py
              
            

Debugging and profiling

pdb

              
# times.py
def times2(number):
    """
    >>> times2(5)
    10
    """
    import pdb; pdb.set_trace()
    return number * 2
              
            

timeit

              
import time

timeit(time.sleep(1))
# 1 loop, best of 3: 1 s per loop
              
            

Software packaging and distribution

Conclusions

Good

• extensive
• general purpose indeed
• check stdlib first before searching for third party libs
• do data processing with collections, itertools, etc
• do CLI, TUI, GUI development

Bad

• unpythonic ¯\_(ツ)_/¯
• hard and cumbersome to use
• third party libraries may be better:
  • python ⇨ ipython
  • pdb ⇨ ipdb
  • urllib ⇨ requests
  • argparse ⇨ click
  • webdev ⇨ django, pyramid, flask