Python Decorators
Decorators is a Python-exclusive feature, virtue of which you can define a function called a decorator function. This decorator function takes an object, manipulates it using its own object and returns this latter object. For example, in the event of decorating a function:
def decoratorFunction(inputFunction):
def manipulateInputFunction():
capture return value of inputFunction
return manipulatedReturnValueOfInputFunction
return manipulateInputFunction
@decoratorFunction
def functionToBeDecorated():
# body of function
returns an object, say a string
Significance of @ Notation
Any call to functionToBeDecorated() translates to decoratorFunction() with functionToBeDecorated as its argument i.e. functionToBeDecorated() becomes decoratorFunction(functionToBeDecorated)(). For example:
stringOne = functionToBeDecorated() BECOMES stringOne = decoratorFunction(functionToBeDecorated)()
Example
Let’s make the output of a function fancier by wrapping its return value with additional text. We will make use of the decorator annotation (@) provided by Python.
def decorateMyFunction(originalFunction):
'''Decorates a function by wrapping its return value in a pair of HTML paragraph tags.'''
def addAdditionalText():
# Obtain string returned by original function
textFromOriginalFunction = originalFunction()
# Adding new functionality to the function being decorated
return "<p>" + textFromOriginalFunction + "</p>"
return addAdditionalText
@decorateMyFunction
def functionToBeDecorated():
'''A simple function that returns a string.'''
return "Hi there!"
print( functionToBeDecorated() ) # OUTPUT: <p>Hi there!</p>
Further Reading
See also:
- Python 101
- Object Oriented Python
- Design Patterns in Python
- 50+ Handy Standard Library Modules
- 60+ Handy Third Library Modules
- 50+ Tips & Tricks for Python Developers
- 50+ Know-How(s) Every Pythonista Must Know