Python.md

is and ==

• is compares equality

• == compares identity

• ex. 2 cats: cat == cat, however using is they are "different cats"

len

len("Hello") #5
len([1, 2, 6, 3, 4]) #5
sorted([5, 4, 3, 2, 1]) #[1, 2, 3, 4, 5]
sorted(["C", "B", "a", str(3), str(1)]) #['1', '3', 'B', 'C', 'a']

pass

• Write a function implementation in the future; Avoid compilation errors
• Ignore if implementation

Functions

• snake_case

def function_a(str1 = "hello"):
    print(str1)
    print("there")

function_a("hi") #hi\nthere
function_a() #hello\nthere

def print_name(first, last):
    print("First:", first, "Last:", last)

print_name(last = "w", first = "d") #First: d Last: w 

# * denotes a list/array
def print_people(*people):
    for person in people:
        print("Name:", person)
  
print_people('a', 'b', 'c', 'd') # Name: 'a' / Name: 'b'...

Classes

class Pokemon
    
    def __init__(self, health, atk):
        self.hp = health
        self.atk = atk
    
    def getStats:
        print(self.hp)
        print(self.atk)
        
Pokemon pikachu(100, 50)
pikachu.getStats() # 100 / 50

File IO

# 'w+' is for writing to file
newfile = open("test.txt", "w+")

string = "The quick brown fox jumps over the lazy dog"

newfile.write(string)

• Writing to a file

Parsing JSON

import json
import os

# if file exists and file is not empty
if os.path.isfile("./test.json") and os.stat("./test.json").st_size != 0:
# open file to read
file_text = open("./test.json", "r+")
data = json.loads(file_text.read()) # returns a Python Dictionary

json.loads()

• Returns a dictionary object from a JSON file

json.dumps()

• Returns a JSON string from a dictionary object

Requests

• pip install requests

import requests

r = requests.get("url")

'''
r.url - url
r.text - html
r.status_code - http code
'''

Advanced Topics

Iterators

An iterator object must implement __iter__() and __next__()

• These 2 functions can be called through iter(obj) and next(obj)
• iter(obj) returns an iterator from the passed in obj
• next(obj) is used to manually iterate through all items of an iterator
  • Reaching the end raises the StopIteration exception
  • For loops on iterators are actually infinite while loops of next() calls until StopIteration is raised
  • Accepts an optional 2nd argument ex. next(obj, 1) which in this example returns 1 upon StopIteration

Generators

Generators are functions that return iterator objects

• To create a generator, define a normal function with a yield statement instead of a return statement
• yield pauses the function and saves its state, continuing on successive calls

Examples

Usage

• Memory friendly implementation of sequences - produces one item at a time
  • Good for infinite streams

Decorators

Decorators takes a function and adds some functionality

def make_pretty(func):
    def inner():
        print("I got decorated")
        func()
    return inner

def ordinary():
    print("I am ordinary")
    
pretty = make_pretty(ordinary)
pretty()
# I got decorated
# I am ordinary

@make_pretty
def ordinary():
    print("I am ordinary")
# Equivalent statements  
def ordinary():
    print("I am ordinary")
ordinary = make_pretty(ordinary)

• @ syntactic sugar