오클랜드 웹개발자 Meetup 스터디 그룹 2018-05-29

study.md

Python High-Level Overview

Key Characteristics

• General-Purpose

• Dynamic Typing

• Concise and Expressive

• "Batteries Included"

• Multi-Paradigm (OOP, FP, etc.)

• Philosophy

  import this
  

Where It's Used

• Web: Django, Flask, Chalice (on AWS), etc.
• Data Science: Jupyter Notebook (Formerly IPython Notebook), TensorFlow, Spark (PySpark), etc.
• Scripting, automation, etc.

Basics

Types

• Boolean: True, False
• String: "hello", 'world'
• Integers: 5, -100
• Floats: 3.14
• None

Arithmetics

• +
• -
• *
• /
• //
• %
• **

Control Flow

• if / elif / else

  if a and b:
      print("Both true!")
  elif a and not b:
      print("Only a true!")
  elif not a and b:
      print("Only b true!")
  else:
      print("Neither true!")
  
  "Both true!" if a and b else "Only one or neither is true!"
  

• for

  for x in [1, 2, 3]:
      print(x)
  

• while

  a = 1
  while a < 10:
      print(a)
      a = a + 1
  

Collections

List

[1, 2, 3]

• Ordered
• Mutable
• (0-)indexed

Slices

words = ["nz", "kr", "dev", "study", "group", "is", "fun"]
words[0]
words[0:3]
words[:3]
words[3:7]
words[3:]

Tuple

(1, 2, 3)

• Ordered
• Immutable
• (0-)indexed
• Multiple return values, variable-length argument list, etc.

Dictionary

{"a": 1, "b": 2}

• Unordered (ordered in 3.6+) key-value pairs, mutable
• Also known as map or hash map in other languages

Set

{1, 2, 2}

• Unordered
• No duplicates
• union, difference, intersection, etc.

Idioms: Comprehensions

List Comprehension

[x for x in "helloworld"]  # ['h', 'e', 'l', 'l', 'o', 'w', 'o', 'r', 'l', 'd']

Dictionary Comprehension

import string
{x: string.ascii_lowercase.index(x) for x in "helloworld"}  # {'h': 7, 'e': 4, 'l': 11, 'o': 14, 'w': 22, 'r': 17, 'd': 3}

Set Comprehension

{x for x in "helloworld"}  # {'r', 'l', 'e', 'd', 'h', 'w', 'o'}

Functions

Basic Syntax

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

def add_nums(*nums):
    return sum(nums)

add_nums(1, 2, 3, 4)  # 10

def add_to(n, to=10):
    return n + to

add_to(20)  # Add 20 to 10 => 30
add_to(50, to=100)  # Add 50 to 100 => 150

def build_msg(template, **vals):
    return template.format(**vals)

build_msg("{a} {b}!", a="hello", b="world")  # "hello world!"

Anonymous Functions

lambda a, b: a + b

Higher-Order Functions

filter(lambda x: x % 2 == 0, range(1, 5))  # [2, 4] when realised
map(lambda x: x ** 2, [2, 4])  # [4, 16] when realised

import functools
functools.reduce(lambda a, b: a + b, range(1, 5))  # 10 == 1 + 2 + 3 + 4

Generators

def doubles(n):
    while n < 10:
        doubled = n * 2
        yield doubled
        n = n + 1

def doubles_infinite(n):
    while True:
        doubled = n * 2
        yield doubled
        n = n + 1

doubles_gen = (x * 2 for x in range(1, 10))

import itertools
doubles_gen_infinite = (x * 2 for x in itertools.count(1))

Tips

• Choose Python 3 (Python 2 is a dead language)
• REPL-driven development (Install ipython!)
• Inspection

  • type

  • dir

  • help

  • ? (view docstring)

  • ?? (view source)

    import this
    this??