Python

>>> print("Hello, World!")
Hello, World!

age = 18      # age is of type int
name = "John" # name is now of type str
print(name)

>>> msg = "Hello, World!"
>>> print(msg[2:5])
llo

mylist = []
mylist.append(1)
mylist.append(2)
for item in mylist:
    print(item) # prints out 1,2

num = 200
if num > 0:
    print("num is greater than 0")
else:
    print("num is not greater than 0")

for item in range(6):
    if item == 3: break
    print(item)
else:
    print("Finally finished!")

>>> def my_function():
...     print("Hello from a function")
...
>>> my_function()
Hello from a function

with open("myfile.txt", "r", encoding='utf8') as file:
    for line in file:
        print(line)

result = 10 + 30 # => 40
result = 40 - 10 # => 30
result = 50 * 5  # => 250
result = 16 / 4  # => 4.0 (Float Division)
result = 16 // 4 # => 4 (Integer Division)
result = 25 % 2  # => 1
result = 5 ** 3  # => 125

counter = 0
counter += 10           # => 10
counter = 0
counter = counter + 10  # => 10

message = "Part 1."

# => Part 1.Part 2.
message += "Part 2."   

>>> website = 'Quickref.ME'
>>> f"Hello, {website}"
"Hello, Quickref.ME"

>>> num = 10
>>> f'{num} + 10 = {num + 10}'
'10 + 10 = 20'

hello = "Hello World"
hello = 'Hello World'

multi_string = """Multiline Strings
Lorem ipsum dolor sit amet,
consectetur adipiscing elit """

x = 1    # int
y = 2.8  # float
z = 1j   # complex

>>> print(type(x))
<class 'int'>

my_bool = True 
my_bool = False

bool(0)     # => False
bool(1)     # => True

list1 = ["apple", "banana", "cherry"]
list2 = [True, False, False]
list3 = [1, 5, 7, 9, 3]
list4 = list((1, 5, 7, 9, 3))

my_tuple = (1, 2, 3)
my_tuple = tuple((1, 2, 3))

set1 = {"a", "b", "c"}   
set2 = set(("a", "b", "c"))

x = int(1)   # x will be 1
y = int(2.8) # y will be 2
z = int("3") # z will be 3

x = float(1)     # x will be 1.0
y = float(2.8)   # y will be 2.8
z = float("3")   # z will be 3.0
w = float("4.2") # w will be 4.2

x = str("s1") # x will be 's1'
y = str(2)    # y will be '2'
z = str(3.0)  # z will be '3.0'

import heapq

myList = [9, 5, 4, 1, 3, 2]
heapq.heapify(myList) # turn myList into a Min Heap
print(myList)    # => [1, 3, 2, 5, 9, 4]
print(myList[0]) # first value is always the smallest in the heap

heapq.heappush(myList, 10) # insert 10
x = heapq.heappop(myList)  # pop and return smallest item
print(x)                   # => 1

myList = [9, 5, 4, 1, 3, 2]
myList = [-val for val in myList] # multiply by -1 to negate
heapq.heapify(myList)

x = heapq.heappop(myList)
print(-x) # => 9 (making sure to multiply by -1 again)

from collections import deque

q = deque()          # empty
q = deque([1, 2, 3]) # with values

q.append(4)     # append to right side
q.appendleft(0) # append to left side
print(q)    # => deque([0, 1, 2, 3, 4])

x = q.pop() # remove & return from right
y = q.popleft() # remove & return from left
print(x)    # => 4
print(y)    # => 0
print(q)    # => deque([1, 2, 3])

q.rotate(1) # rotate 1 step to the right
print(q)    # => deque([3, 1, 2])

>>> hello = "Hello, World"
>>> print(hello[1])
e
>>> print(hello[-1])
d

>>> for char in "foo":
...     print(char)
f
o
o

 ┌───┬───┬───┬───┬───┬───┬───┐
 | m | y | b | a | c | o | n |
 └───┴───┴───┴───┴───┴───┴───┘
 0   1   2   3   4   5   6   7
-7  -6  -5  -4  -3  -2  -1

>>> s = 'mybacon'
>>> s[2:5]
'bac'
>>> s[0:2]
'my'

>>> s = 'mybacon'
>>> s[:2]
'my'
>>> s[2:]
'bacon'
>>> s[:2] + s[2:]
'mybacon'
>>> s[:]
'mybacon'

>>> s = 'mybacon'
>>> s[-5:-1]
'baco'
>>> s[2:6]
'baco'

>>> s = '12345' * 5
>>> s
'1234512345123451234512345'
>>> s[::5]
'11111'
>>> s[4::5]
'55555'
>>> s[::-5]
'55555'
>>> s[::-1]
'5432154321543215432154321'

>>> hello = "Hello, World!"
>>> print(len(hello))
13

>>> s = '===+'
>>> n = 8
>>> s * n
'===+===+===+===+===+===+===+===+'

>>> s = 'spam'
>>> s in 'I saw spamalot!'
True
>>> s not in 'I saw The Holy Grail!'
True

>>> s = 'spam'
>>> t = 'egg'
>>> s + t
'spamegg'
>>> 'spam' 'egg'
'spamegg'

name = "John"
print("Hello, %s!" % name)

name = "John"
age = 23
print("%s is %d years old." % (name, age))

txt1 = "My name is {fname}, I'm {age}".format(fname="John", age=36)
txt2 = "My name is {0}, I'm {1}".format("John", 36)
txt3 = "My name is {}, I'm {}".format("John", 36)

>>> name = input("Enter your name: ")
Enter your name: Tom
>>> name
'Tom'

>>> "#".join(["John", "Peter", "Vicky"])
'John#Peter#Vicky'

>>> "Hello, world!".endswith("!")
True

>>> website = 'Quickref.ME'
>>> f"Hello, {website}"
"Hello, Quickref.ME"

>>> num = 10
>>> f'{num} + 10 = {num + 10}'
'10 + 10 = 20'

>>> f"""He said {"I'm John"}"""
"He said I'm John"

>>> f'5 {"{stars}"}'
'5 {stars}'
>>> f'{{5}} {"stars"}'
'{5} stars'

>>> name = 'Eric'
>>> age = 27
>>> f"""Hello!
...     I'm {name}.
...     I'm {age}."""
"Hello!\n    I'm Eric.\n    I'm 27."

>>> f'{"text":10}'     # [width]
'text      '
>>> f'{"test":*>10}'   # fill left
'******test'
>>> f'{"test":*<10}'   # fill right
'test******'
>>> f'{"test":*^10}'   # fill center
'***test***'
>>> f'{12345:0>10}'    # fill with numbers
'0000012345'

>>> f'{10:b}'        # binary type
'1010'
>>> f'{10:o}'        # octal type
'12'
>>> f'{200:x}'       # hexadecimal type
'c8'
>>> f'{200:X}'
'C8'
>>> f'{345600000000:e}' # scientific notation
'3.456000e+11'
>>> f'{65:c}'       # character type
'A'
>>> f'{10:#b}'      # [type] with notation (base)
'0b1010'
>>> f'{10:#o}'
'0o12'
>>> f'{10:#x}'
'0xa'

>>> f'{-12345:0=10}'  # negative numbers
'-000012345'
>>> f'{12345:010}'    # [0] shortcut (no align)
'0000012345'
>>> f'{-12345:010}'
'-000012345'
>>> import math       # [.precision]
>>> math.pi
3.141592653589793
>>> f'{math.pi:.2f}'
'3.14'
>>> f'{1000000:,.2f}' # [grouping_option]
'1,000,000.00'
>>> f'{1000000:_.2f}'
'1_000_000.00'
>>> f'{0.25:0%}'      # percentage
'25.000000%'
>>> f'{0.25:.0%}'
'25%'

>>> f'{12345:+}'      # [sign] (+/-)
'+12345'
>>> f'{-12345:+}'
'-12345'
>>> f'{-12345:+10}'
'    -12345'
>>> f'{-12345:+010}'
'-000012345'

>>> li1 = []
>>> li1
[]
>>> li2 = [4, 5, 6]
>>> li2
[4, 5, 6]
>>> li3 = list((1, 2, 3))
>>> li3
[1, 2, 3]
>>> li4 = list(range(1, 11))
>>> li4
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

>>> list(filter(lambda x : x % 2 == 1, range(1, 20)))
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]

>>> [x ** 2 for x in range (1, 11) if  x % 2 == 1]
[1, 9, 25, 49, 81]

>>> [x for x in [3, 4, 5, 6, 7] if x > 5]
[6, 7]

>>> list(filter(lambda x: x > 5, [3, 4, 5, 6, 7]))
[6, 7]

>>> li = []
>>> li.append(1)
>>> li
[1]
>>> li.append(2)
>>> li
[1, 2]
>>> li.append(4)
>>> li
[1, 2, 4]
>>> li.append(3)
>>> li
[1, 2, 4, 3]

a_list[start:end]
a_list[start:end:step]

>>> a = ['spam', 'egg', 'bacon', 'tomato', 'ham', 'lobster']
>>> a[2:5]
['bacon', 'tomato', 'ham']
>>> a[-5:-2]
['egg', 'bacon', 'tomato']
>>> a[1:4]
['egg', 'bacon', 'tomato']

>>> a[:4]
['spam', 'egg', 'bacon', 'tomato']
>>> a[0:4]
['spam', 'egg', 'bacon', 'tomato']
>>> a[2:]
['bacon', 'tomato', 'ham', 'lobster']
>>> a[2:len(a)]
['bacon', 'tomato', 'ham', 'lobster']
>>> a
['spam', 'egg', 'bacon', 'tomato', 'ham', 'lobster']
>>> a[:]
['spam', 'egg', 'bacon', 'tomato', 'ham', 'lobster']

['spam', 'egg', 'bacon', 'tomato', 'ham', 'lobster']
>>> a[0:6:2]
['spam', 'bacon', 'ham']
>>> a[1:6:2]
['egg', 'tomato', 'lobster']
>>> a[6:0:-2]
['lobster', 'tomato', 'egg']
>>> a
['spam', 'egg', 'bacon', 'tomato', 'ham', 'lobster']
>>> a[::-1]
['lobster', 'ham', 'tomato', 'bacon', 'egg', 'spam']

>>> li = ['bread', 'butter', 'milk']
>>> li.pop()
'milk'
>>> li
['bread', 'butter']
>>> del li[0]
>>> li
['butter']

>>> li = ['a', 'b', 'c', 'd']
>>> li[0]
'a'
>>> li[-1]
'd'
>>> li[4]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list index out of range

>>> odd = [1, 3, 5]
>>> odd.extend([9, 11, 13])
>>> odd
[1, 3, 5, 9, 11, 13]
>>> odd = [1, 3, 5]
>>> odd + [9, 11, 13]
[1, 3, 5, 9, 11, 13]

>>> li = [3, 1, 3, 2, 5]
>>> li.sort()
>>> li
[1, 2, 3, 3, 5]
>>> li.reverse()
>>> li
[5, 3, 3, 2, 1]

>>> li = [3, 1, 3, 2, 5]
>>> li.count(3)
2

>>> li = ["re"] * 3
>>> li
['re', 're', 're']

num = 5
if num > 10:
    print("num is totally bigger than 10.")
elif num < 10:
    print("num is smaller than 10.")
else:
    print("num is indeed 10.")

>>> a = 330
>>> b = 200
>>> r = "a" if a > b else "b"
>>> print(r)
a

value = True
if not value:
    print("Value is False")
elif value is None:
    print("Value is None")
else:
    print("Value is True")

x = 1
match x:
  case 0:
    print("zero")
  case 1:
    print("one")
  case _:
    print("multiple")

primes = [2, 3, 5, 7]
for prime in primes:
    print(prime)

animals = ["dog", "cat", "mouse"]
# enumerate() adds counter to an iterable
for i, value in enumerate(animals):
    print(i, value)

x = 0
while x < 4:
    print(x)
    x += 1  # Shorthand for x = x + 1

x = 0
for index in range(10):
    x = index * 10
    if index == 5:
    	break
    print(x)

for index in range(3, 8): 
    x = index * 10
    if index == 5:
    	continue
    print(x)

for i in range(4):
    print(i) # Prints: 0 1 2 3

for i in range(4, 8):
    print(i) # Prints: 4 5 6 7

for i in range(4, 10, 2):
    print(i) # Prints: 4 6 8

words = ['Mon', 'Tue', 'Wed']
nums = [1, 2, 3]
# Use zip to pack into a tuple list
for w, n in zip(words, nums):
    print('%d:%s, ' %(n, w))

nums = [60, 70, 30, 110, 90]
for n in nums:
    if n > 100:
        print("%d is bigger than 100" %n)
        break
else:
    print("Not found!")

def hello_world():  
    print('Hello, World!')

def add(x, y):
    print("x is %s, y is %s" %(x, y))
    return x + y

add(5, 6)    # => 11

def varargs(*args):
    return args

varargs(1, 2, 3)  # => (1, 2, 3)

def keyword_args(**kwargs):
    return kwargs

# => {"big": "foot", "loch": "ness"}
keyword_args(big="foot", loch="ness")

def swap(x, y):
    return y, x

x = 1
y = 2
x, y = swap(x, y)  # => x = 2, y = 1

def add(x, y=10):
    return x + y

add(5)      # => 15
add(5, 20)  # => 25

# => True
(lambda x: x > 2)(3)

# => 5
(lambda x, y: x ** 2 + y ** 2)(2, 1)

import math
print(math.sqrt(16))  # => 4.0

from math import ceil, floor
print(ceil(3.7))   # => 4.0
print(floor(3.7))  # => 3.0

from math import *

import math as m

# => True
math.sqrt(16) == m.sqrt(16)

import math
dir(math)

with open("myfile.txt") as file:
    for line in file:
        print(line)

file = open('myfile.txt', 'r')
for i, line in enumerate(file, start=1):
    print("Number %s: %s" % (i, line))

contents = {"aa": 12, "bb": 21}
with open("myfile1.txt", "w+") as file:
    file.write(str(contents))

with open('myfile1.txt', "r+") as file:
    contents = file.read()
print(contents)

contents = {"aa": 12, "bb": 21}
with open("myfile2.txt", "w+") as file:
    file.write(json.dumps(contents))

with open('myfile2.txt', "r+") as file:
    contents = json.load(file)
print(contents)

import os
os.remove("myfile.txt")

import os
if os.path.exists("myfile.txt"):
    os.remove("myfile.txt")
else:
    print("The file does not exist")

import os
os.rmdir("myfolder")

class MyNewClass:
    pass

# Class Instantiation
my = MyNewClass()

class Animal:
    def __init__(self, voice):
        self.voice = voice
 
cat = Animal('Meow')
print(cat.voice)    # => Meow
 
dog = Animal('Woof') 
print(dog.voice)    # => Woof

class Dog:

    # Method of the class
    def bark(self):
        print("Ham-Ham")
 
charlie = Dog()
charlie.bark()   # => "Ham-Ham"

class MyClass:
    class_variable = "A class variable!"

# => A class variable!
print(MyClass.class_variable)

x = MyClass()
 
# => A class variable!
print(x.class_variable)

class ParentClass:
    def print_test(self):
        print("Parent Method")
 
class ChildClass(ParentClass):
    def print_test(self):
        print("Child Method")
        # Calls the parent's print_test()
        super().print_test() 

>>> child_instance = ChildClass()
>>> child_instance.print_test()
Child Method
Parent Method

class Employee:
    def __init__(self, name):
        self.name = name
 
    def __repr__(self):
        return self.name
 
john = Employee('John')
print(john)  # => John

class CustomError(Exception):
    pass

class ParentClass:
    def print_self(self):
        print('A')
 
class ChildClass(ParentClass):
    def print_self(self):
        print('B')
 
obj_A = ParentClass()
obj_B = ChildClass()
 
obj_A.print_self() # => A
obj_B.print_self() # => B

class ParentClass:
    def print_self(self):
        print("Parent")
 
class ChildClass(ParentClass):
    def print_self(self):
        print("Child")
 
child_instance = ChildClass()
child_instance.print_self() # => Child

class Animal: 
    def __init__(self, name, legs):
        self.name = name
        self.legs = legs
        
class Dog(Animal):
    def sound(self):
        print("Woof!")
 
Yoki = Dog("Yoki", 4)
print(Yoki.name) # => YOKI
print(Yoki.legs) # => 4
Yoki.sound()     # => Woof!

string: str = "ha"
times: int = 3


# wrong hit, but run correctly
result: str = 1 + 2
print(result)  # => 3


def say(name: str, start: str = "Hi"):
    return start + ", " + name

print(say("Python"))  # => Hi, Python

from typing import Dict, Tuple, List

bill: Dict[str, float] = {
    "apple": 3.14,
    "watermelon": 15.92,
    "pineapple": 6.53,
}
completed: Tuple[str] = ("DONE",)
succeeded: Tuple[int, str] = (1, "SUCCESS")
statuses: Tuple[str, ...] = (
    "DONE", "SUCCESS", "FAILED", "ERROR",
)
codes: List[int] = (0, 1, -1, -2)

bill: dict[str, float] = {
    "apple": 3.14,
    "watermelon": 15.92,
    "pineapple": 6.53,
}
completed: tuple[str] = ("DONE",)
succeeded: tuple[int, str] = (1, "SUCCESS")
statuses: tuple[str, ...] = (
    "DONE", "SUCCESS", "FAILED", "ERROR",
)
codes: list[int] = (0, 1, -1, -2)

def calc_summary(*args: int):
    return sum(args)

print(calc_summary(3, 1, 4))  # => 8

def say_hello(name) -> str:
    return "Hello, " + name

var = "Python"
print(say_hello(var))  # => Hello, Python

from typing import Union

def resp200(meaningful) -> Union[int, str]:
    return "OK" if meaningful else 200

def calc_summary(**kwargs: int):
    return sum(kwargs.values())

print(calc_summary(a=1, b=2))  # => 3

def resp200() -> (int, str):
    return 200, "OK"

returns = resp200()
print(returns)  # => (200, 'OK')
print(type(returns))  # tuple

def resp200(meaningful) -> int | str:
    return "OK" if meaningful else 200

class Employee:
    name: str
    age: int

    def __init__(self, name, age):
        self.name = name
        self.age = age
        self.graduated: bool = False

class Employee:
    name: str

    def set_name(self, name) -> "Employee":
        self.name = name
        return self

    def copy(self) -> 'Employee':
        return type(self)(self.name)

from typing import Self

class Employee:
    name: str
    age: int

    def set_name(self: Self, name) -> Self:
        self.name = name
        return self

from typing import TypeVar, Type

T = TypeVar("T")

# "mapper" is a type, like int, str, MyClass and so on.
# "default" is an instance of type T, such as 314, "string", MyClass() and so on.
# returned is an instance of type T too.
def converter(raw, mapper: Type[T], default: T) -> T:
    try:
        return mapper(raw)
    except:
        return default

raw: str = input("Enter an integer: ")
result: int = converter(raw, mapper=int, default=0)

from typing import TypeVar, Callable, Any

T = TypeVar("T")

def converter(raw, mapper: Callable[[Any], T], default: T) -> T:
    try:
        return mapper(raw)
    except:
        return default

# Callable[[Any], ReturnType] means a function declare like:
# def func(arg: Any) -> ReturnType:
#     pass

# Callable[[str, int], ReturnType] means a function declare like:
# def func(string: str, times: int) -> ReturnType:
#     pass

# Callable[..., ReturnType] means a function declare like:
# def func(*args, **kwargs) -> ReturnType:
#     pass

def is_success(value) -> bool:
    return value in (0, "OK", True, "success")

resp = dict(code=0, message="OK", data=[])
successed: bool = converter(resp.message, mapper=is_success, default=False)

# This is a single line comments.

""" Multiline strings can be written
    using three "s, and are often used
    as documentation.
"""

''' Multiline strings can be written
    using three 's, and are often used
    as documentation.
'''

def double_numbers(iterable):
    for i in iterable:
        yield i + i

values = (-x for x in [1,2,3,4,5])
gen_to_list = list(values)

# => [-1, -2, -3, -4, -5]
print(gen_to_list)

try:
    # Use "raise" to raise an error
    raise IndexError("This is an index error")
except IndexError as e:
    pass                 # Pass is just a no-op. Usually you would do recovery here.
except (TypeError, NameError):
    pass                 # Multiple exceptions can be handled together, if required.
else:                    # Optional clause to the try/except block. Must follow all except blocks
    print("All good!")   # Runs only if the code in try raises no exceptions
finally:                 # Execute under all circumstances
    print("We can clean up resources here")