python-adv.py

from contextlib import contextmanager
from time import time, sleep

# decorators
def timer(func):
  def f(*args, **kwargs):
    before = time()
    rv = func(*args, **kwargs)
    after = time()
    print(f"Time taken = {after- before}")
    return rv
  return f

@timer
def dummy(N):
  for i in range(N):
    print("Sleeping for 0.1 secs")
    sleep(0.1)

# generators & decorators
def gen_timer(func):
  def f(*args, **kwargs):
    before = time()
    for rv in func(*args, **kwargs):
      yield rv
    after = time()
    print(f"Time taken = {after- before}")
  return f

@gen_timer
def generate(N):
  for i in range(10):
    # time taken to get data from somewhere
    sleep(0.1)
    yield i

# context managers
def open_database(name):
  # open the database
  print("Database opened")
  # return the file descriptor
  return 0 

def close_database(f):
  # must call after open_database
  print("Database closed")

@contextmanager
def opendb(name):
  try:
    assert isinstance(name, str)
    f = open_database(name)
    yield f
  except Exception as e:
    print(f"[ERROR] {e}")
  finally:
    try:
      close_database(f)
    except:
      pass

if __name__ == '__main__':
  # check decorator
  dummy(10)

  # check generator
  for i in generate(10):
    print(i)

  # check context manager
  with opendb("yash") as f:
    print(f"The returned dummy file descriptor is {f}")

  with opendb(23) as f:
    print(f"The returned dummy file descriptor is {f}")