Python 装饰器实现DRY(不重复代码)原则

def handle_request(request):
  return HttpResponse("Hello, World")

def register(request):
  result = None
  # check for post only
  if request.method != 'POST':
    result = {"error": "this method only accepts posts!"}
  else:
    try:
      user = User.objects.create_user(request.POST['username'],
                      request.POST['email'],
                      request.POST['password'])
      # optional fields
      for field in ['first_name', 'last_name']:
        if field in request.POST:
          setattr(user, field, request.POST[field])
      user.save()
      result = {"success": True}
    except KeyError as e:
      result = {"error": str(e) }
  response = HttpResponse(json.dumps(result))
  if "error" in result:
    response.status_code = 500
  return response

# a decorator receives the method it's wrapping as a variable 'f'
def increment(f):
  # we use arbitrary args and keywords to
  # ensure we grab all the input arguments.
  def wrapped_f(*args, **kw):
    # note we call f against the variables passed into the wrapper,
    # and cast the result to an int and increment .
    return int(f(*args, **kw)) + 1
  return wrapped_f # the wrapped function gets returned.

@increment
def plus(a, b):
  return a + b
 result = plus(4, 6)
assert(result == 11, "We wrote our decorator wrong!")

def post_only(f):
  """ Ensures a method is post only """
  def wrapped_f(request):
    if request.method != "POST":
      response = HttpResponse(json.dumps(
        {"error": "this method only accepts posts!"}))
      response.status_code = 500
      return response
    return f(request)
  return wrapped_f

@post_only
def register(request):
  result = None
  try:
    user = User.objects.create_user(request.POST['username'],
                    request.POST['email'],
                    request.POST['password'])
    # optional fields
    for field in ['first_name', 'last_name']:
      if field in request.POST:
        setattr(user, field, request.POST[field])
    user.save()
    result = {"success": True}
  except KeyError as e:
    result = {"error": str(e) }
  response = HttpResponse(json.dumps(result))
  if "error" in result:
    response.status_code = 500
  return response

def json_response(f):
  """ Return the response as json, and return a 500 error code if an error exists """
  def wrapped(*args, **kwargs):
    result = f(*args, **kwargs)
    response = HttpResponse(json.dumps(result))
    if type(result) == dict and 'error' in result:
      response.status_code = 500
    return response

@post_only
@json_response
def register(request):
  try:
    user = User.objects.create_user(request.POST['username'],
                    request.POST['email'],
                    request.POST['password'])
    # optional fields
    for field in ['first_name', 'last_name']:
      if field in request.POST:
        setattr(user, field, request.POST[field])
    user.save()
    return {"success": True}
  except KeyError as e:
    return {"error": str(e) }

@post_only
@json_response
def login(request):
  if request.user is not None:
    return {"error": "User is already authenticated!"}
  user = auth.authenticate(request.POST['username'], request.POST['password'])
  if user is not None:
    if not user.is_active:
      return {"error": "User is inactive"}
    auth.login(request, user)
    return {"success": True, "id": user.pk}
  else:
    return {"error": "User does not exist with those credentials"}

def parameterize_request(types=("POST",)):
  """
  Parameterize the request instead of parsing the request directly.
  Only the types specified will be added to the query parameters.
  e.g. convert a=test

@post_only
@json_response
@parameterize_request(["POST"])
def register(request, username, email, password,
       first_name=None, last_name=None):
  user = User.objects.create_user(username, email, password)
  user.first_name=first_name
  user.last_name=last_name
  user.save()
  return {"success": True}

def increment(f):
  """ Increment a function result """
  wrapped_f(a, b):
    return f(a, b) + 1
  return wrapped_f
@increment
def plus(a, b)
  """ Add two things together """
  return a + b
plus.__name__ # this is now 'wrapped_f' instead of 'plus'
plus.__doc__  # this now returns 'Increment a function result' instead of 'Add two things together'

from functools import wraps
def increment(f):
  """ Increment a function result """
  @wraps(f)
  wrapped_f(a, b):
    return f(a, b) + 1
  return wrapped_f
@increment
def plus(a, b)
  """ Add two things together """
  return a + b
 
plus.__name__ # this returns 'plus'
plus.__doc__  # this returns 'Add two things together'

$ sudo easy_install decorator

$ pip install decorator

from decorator import decorator
@decorator
def post_only(f, request):
  """ Ensures a method is post only """
  if request.method != "POST":
    response = HttpResponse(json.dumps(
      {"error": "this method only accepts posts!"}))
    response.status_code = 500
    return response
  return f(request)