import sys
import os
def blockPrint():
    sys.stdout = open(os.devnull, 'w')
def enablePrint():
    sys.stdout = sys.__stdout__
blockPrint()

# ok so instead of using len - 1, we can just use -1, which is len - 1, if len = 4, then this is 4 - 1 = 3.
# alright cool.
list = [1,23,4]
print(list[-2])
# and i and j is inclusive and exclusive
a = '1234'
print(a[1:2])
# omitting and :j is start to j, inclusive to exclusive
print(a[0:2])
print(a[:2])
# omitting and i: is inclusive to at the end, including all
print(a[0:])
# omitting all and just [:] gives a copy returned.
print(a[:])

# ok so when doing multiple complehension u must have in correct order from left to right, likst like u normally do
list_of_lists = [['4', '8'], ['4', '2', '28'], ['1', '12'], ['3', '6', '2']]
print([int(i) for sublist in list_of_lists for i in sublist])

message = 'David is cool'
print(message[0:10:2])
print([x for x in range(0, 10, 2)])
# [0, 2, 4, 6, 8]
print([x for x in range(10, 0, -1)])  # reverse!
# [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

#  if index with 3, then start(inclusive), end(exclusive), step added to start
print(message[:4:-1])  # start to index 4, 0 -1, 0 -2, which is -1, -2, index max, max - 1, stop count from beginning
# 'looc si ',           max len 13, this is 8. so 13 - 4 = 8
print(message[::-1])  # this reverse the string!

# f'string' with {evaluate math, etc. expression}
print(f'hello world')


# 'OMG' we can set up the default value of function parameter
# def function(order_matter_variable_without_default_go_first!, set_as_default = 1)
# if there is specfic value, then no longer default value!
# DO NOT DO NOT DO NOT EVER AND EVER! SIMPLY MUTATE!
# def add_num(num: int, numbers: list[int] = []) -> list[int]:
#     """Append num to the given numbers, and return the list.
#
#     If no numbers are given, return a new list containing just num.
#
#     >>> my_numbers = [1, 2, 3]
#     >>> add_num(10, my_numbers)
#     [1, 2, 3, 10]
#     >>> add_num(10)
#     [10]
#     """
#     numbers.append(num)
#     return numbers
# >>> add_num(10)
# [10]                # Looks okay...
# >>> add_num(20)
# [10, 20]            # Wait, what? Should be [20]...
# >>> add_num(30)
# [10, 20, 30]        # ??? Should be [30]...
# >>> add_num(40)
# [10, 20, 30, 40]    # I see the pattern, but why?!

# alternate method
# from typing import Optional
# def add_num(num: int, numbers: Optional[list[int]] = None) -> list[int]:
#     """Append num to the given numbers, and return the list.
#
#     If no numbers are given, return a new list containing just num.
#
#     >>> my_numbers = [1, 2, 3]
#     >>> add_num(10, my_numbers)
#     [1, 2, 3, 10]
#     >>> add_num(10)
#     [10]
#     """
#     if numbers is None:
#         return [num]
#     else:
#         numbers.append(num)
#         return numbers