Decorators (Slideshow)

The Ominous “@”

• Special syntax ⟶ only syntactic sugar

• Used to wrap existing functions/methods

  • Without modifying them

• Examples

  • Debugging: printing function name and arguments

  • Timing information: time spent inside a function

  • Adding a D-Bus interface to a plain Python class

  • Defining Flask URL routes to call Python functions

  • …

What and How

• Only syntactic sugar for inner functions/closures (see Closures)

• Can be implemented as functions

@debug
def bar(a, b, c):
    ...

• Can be implemented as classes (usually when decorator is parameterized ⟶ state needs to be remembered)

@debug(prefix)
def bar(a, b, c):
    ...