# Author: Huahua
class MyListIterator:
  def __init__(self, my_list, index=0):
    self.my_list = my_list
    self.index = index

  def __next__(self):
    if self.index < len(self.my_list.data):
      val = self.my_list.data[self.index]
      self.index += 1
      return val
    else:
      raise StopIteration()

  def __iter__(self):
    return MyListIterator(self.my_list, self.index)
    # return self

class MyList:
  def __init__(self, data):
    self.data = list(data)

  def __getitem__(self, index):
    return self.data[index]

  def __len__(self):
    return len(self.data)

  def __iter__(self):
    return MyListIterator(self)

my_list = MyList([1,2,3,4,5])
it = iter(my_list)
next(it)
it2 = iter(it)
next(it)
print('--- it ---')
for x in it:
  print(x) # 3, 4, 5
print('--- it2 ---')
for x in it2:
  print(x) # 2, 3, 4, 5

// Author: Huahua
import re
import io

# Example 1:
a = [0] * 100
if len(a) > 10:
  print(f"List is too long ({len(a)} elements, expected <= 10)")

n = len(a)
if n > 10:
  print(f"List is too long ({n} elements, expected <= 10)")

if (x := len(a)) > 10:
  print(f"List is too long ({x} elements, expected <= 10)")

# Example 2, bad
ads = "Now 20% off till 6/18"

m1 = re.search(r'(\d+)% off', ads)
discount1 = float(m1.group(1)) / 100 if m1 else 0.0

discount2 = float(m2.group(1)) / 100 if (m2 := re.search(r'(\d+)% off', ads)) else 0.0

print(f'{discount1 = }, {discount2 = }')

# Example 3
f1 = io.StringIO("123456789")
x1 = f1.read(4)
while x1 != '':
  print(x1)
  x1 = f1.read(4)

f2 = io.StringIO("123456789")
while (x2 := f2.read(4)) != '':
  print(x2)

# Example 4
prog_langs = {'c++', 'python', 'java'}
langs = ['C++', 'Java', 'PYthon', 'English', '中文']

l1 = [lang.lower() for lang in langs if lang.lower() in prog_langs]
print(l1)

l2 = [l for lang in langs if (l := lang.lower()) in prog_langs]
print(l2)

name = 'Huahua'
score = 123.456789

print('name = ' + name + ', score = ' + str(score))
print('name = %s, score = %.3f' % (name, score))
print('name = {name}, score = {score:.3f}'.format(name=name, score=score))
print('name = {name}, score = {score:.3f}'.format(name='Huahua', score=123.456789))

print(f'name = {name}, score = {score:.3f}') # Python 3.6
print(f'{name = }, {score = :.3f}') # Python 3.8

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

k = 1
print(f'{k = }, {add(k, 2) = }') # k = 1, add(k, 2) = 3