syntax – What does the at (@) symbol do in Python?
syntax – What does the at (@) symbol do in Python?
An @ symbol at the beginning of a line is used for class, function and method decorators.
Read more here:
The most common Python decorators youll run into are:
If you see an @ in the middle of a line, thats a different thing, matrix multiplication. See this answer showing the use of @ as a binary operator.
Example
class Pizza(object):
def __init__(self):
self.toppings = []
def __call__(self, topping):
# When using @instance_of_pizza before a function definition
# the function gets passed onto topping.
self.toppings.append(topping())
def __repr__(self):
return str(self.toppings)
pizza = Pizza()
@pizza
def cheese():
return cheese
@pizza
def sauce():
return sauce
print pizza
# [cheese, sauce]
This shows that the function/method/class youre defining after a decorator is just basically passed on as an argument to the function/method immediately after the @ sign.
First sighting
The microframework Flask introduces decorators from the very beginning in the following format:
from flask import Flask
app = Flask(__name__)
@app.route(/)
def hello():
return Hello World!
This in turn translates to:
rule = /
view_func = hello
# They go as arguments here in flask/app.py
def add_url_rule(self, rule, endpoint=None, view_func=None, **options):
pass
Realizing this finally allowed me to feel at peace with Flask.
syntax – What does the at (@) symbol do in Python?
This code snippet:
def decorator(func):
return func
@decorator
def some_func():
pass
Is equivalent to this code:
def decorator(func):
return func
def some_func():
pass
some_func = decorator(some_func)
In the definition of a decorator you can add some modified things that wouldnt be returned by a function normally.