python-decorators

Examples

Wrapping a simple logic

A decorator can be used to wrap a simple piece of logic to the decorated function.

It does so by creating a new function, injecting the logic, and calling the original function to retrieve the result.

• Example 1

  def require_http_methods(request_method_list):
      """
      Decorator to make a view only accept particular request methods.  Usage::
  
          @require_http_methods(["GET", "POST"])
          def my_view(request):
              # I can assume now that only GET or POST requests make it this far
              # ...
  
      Note that request methods should be in uppercase.
      """
      def decorator(func):
          @wraps(func, assigned=available_attrs(func))
          def inner(request, *args, **kwargs):
              if request.method not in request_method_list:
                  logger.warning(
                      'Method Not Allowed (%s): %s', request.method, request.path,
                      extra={'status_code': 405, 'request': request}
                  )
                  return HttpResponseNotAllowed(request_method_list)
              return func(request, *args, **kwargs)
          return inner
      return decorator
  
  require_GET = require_http_methods(["GET"])
  require_GET.__doc__ = "Decorator to require that a view only accepts the GET method."
  
  require_POST = require_http_methods(["POST"])
  require_POST.__doc__ = "Decorator to require that a view only accepts the POST method."
  

    from django.views.decorators.http import require_GET, require_POST
    from django.contrib.auth.decorators import login_required
    from django.contrib.admin.views.decorators import staff_member_required
    from django.shortcuts import redirect, render
    from django.core.urlresolvers import reverse
  
    @require_GET
    def index(request):
        return HttpResponse("Hello, world!")
  
    @require_GET
    @login_required
    def dashboard(request):
        return render(request, 'dashboard.html')
  
    @require_POST
    @staff_member_required
    def add(request):
        # ...
        return redirect(reverse('dashboard'))
  

  For readability, it is often a good practice that this kind of decorator does not change the signature (i.e. parameters and return type) of the decorated function. In the example above each function is a Django view, and after being decorated they are still Django views.

• Example 2

  (Script available)

    import time
    import functools
  
    def timed(func):
        @functools.wraps(func)
        def __new_func(*args, **kwargs):
            start = time.time()
            try:
                return func(*args, **kwargs)
            finally:
                end = time.time()
                print("{} took {} seconds".format(func.__name__, end - start))
  
        return __new_func
  
    @timed
    def f(x):
        for i in range(10 ** x):
            pass
  
    if __name__ == '__main__':
        f(5)
        f(6)
        f(7)
        f(8)
  

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