Real-world examples

Writing Functions in Python

Shayne Miel

Software Architect @ Duo Security

Time a function

import time

def timer(func):
  """A decorator that prints how long a function took to run.

  Args:
    func (callable): The function being decorated.

  Returns:
    callable: The decorated function.
  """

import time

def timer(func):
  """A decorator that prints how long a function took to run."""

  # Define the wrapper function to return.
  def wrapper(*args, **kwargs):

    # When wrapper() is called, get the current time.
    t_start = time.time()

    # Call the decorated function and store the result.
    result = func(*args, **kwargs)

    # Get the total time it took to run, and print it.
    t_total = time.time() - t_start
    print('{} took {}s'.format(func.__name__, t_total))

    return result

  return wrapper

Using timer()

@timer
def sleep_n_seconds(n):
  time.sleep(n)

sleep_n_seconds(5)

sleep_n_seconds took 5.0050950050354s

sleep_n_seconds(10)

sleep_n_seconds took 10.010067701339722s

def memoize(func):
  """Store the results of the decorated function for fast lookup
  """

  # Store results in a dict that maps arguments to results
  cache = {}

  # Define the wrapper function to return.
  def wrapper(*args, **kwargs):
    # Define a hashable key for 'kwargs'.
    kwargs_key = tuple(sorted(kwargs.items()))

    # If these arguments haven't been seen before,
    if (args, kwargs_key) not in cache:

      # Call func() and store the result.
      cache[(args, kwargs_key)] = func(*args, **kwargs)

    return cache[(args, kwargs_key)]

  return wrapper

@memoize
def slow_function(a, b):
  print('Sleeping...')
  time.sleep(5)
  return a + b

slow_function(3, 4)

Sleeping...

7

slow_function(3, 4)

When to use decorators

Add common behavior to multiple functions

@timer
def foo():
  # do some computation

@timer
def bar():
  # do some other computation

@timer
def baz():
  # do something else

Let's practice!

Writing Functions in Python