Python Decorators: An Intro

All the hip frameworks have them, you see them scattered around your codebase, but what IS a decorator? In this talk, Bill Israel will cover the features of Python that make decorators possible, how they work under the hood, what they're good for, and how you can start writing your own.

Transcript

1. @python.decorators pynash · september 25, 2014
3. @epochblue
4. @epochblue
5. def get_user_profile():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 user = users.get(user_id)
 return jsonify(user=user.to_json())
 
 
 def create_user():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 user = users.get(session.get('user_id'))
 if not user.has_role('admin'):
 abort(401)
 
 data = request.get_json()
 new_user = users.create(**data)
 return jsonify(user=new_user.to_json()), 201
6. @login_required
 def get_user_profile():
 user = users.get(session.get(‘user_id')
 return jsonify(user=user.to_json())
 
 
 @login_required
 @role_required('admin')
 def create_user():
 data = request.get_json()
 new_user = users.create(**data)
 return jsonify(user=new_user.to_json()), 201
7. A Quick Note
8. def get_user_profile():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 user = users.get(user_id)
 return jsonify(user=user.to_json())
9. def get_user_profile():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 user = users.get(user_id)
 return jsonify(user=user.to_json())
10. But first...
11. Let’s talk about functions
12. def example():
 print("I'm a function!")
13. >>> example() I'm a function! def example():
 print("I'm a function!")
14. First-Class Functions
15. Save functions into variables
16. def example():
 print("I'm a function!")
17. def example():
 print("I'm a function!") >>> f = example >>> f() I'm a function!
18. Pass functions as arguments
19. def example():
 print("I'm a function!")
20. def example():
 print("I'm a function!") def first_class(func):
 func()
21. def example():
 print("I'm a function!") >>> first_class(example) I'm a function! def first_class(func):
 func()
22. Return functions from functions
23. def example():
 print("I'm a function!")
24. def example():
 print("I'm a function!") def first_class2():
 return example
25. def example():
 print("I'm a function!") >>> f = first_class2() >>> f() I'm a function! def first_class2():
 return example
26. Nest functions inside functions
27. def fist_class3():
 msg = "I'm a function!"
 
 def example():
 print(msg)
 
 example()
28. def fist_class3():
 msg = "I'm a function!"
 
 def example():
 print(msg)
 
 example() >>> first_class3() I'm a function!
29. First-Class Functions
30. Save functions into variables
31. Return functions from functions Save functions into variables
32. Pass functions as arguments Save functions into variables Return functions from functions
33. Nest functions inside functions Save functions into variables Pass functions as arguments Return functions from functions
34. Return functions from functions Pass functions as arguments Nest functions inside functions Save functions into variables
35. Return functions from functions Pass functions as arguments Nest functions inside functions Save functions into variables Decorators
36. def decorator(func):
 def wrapper():
 print("I'm a wrapper.")
 func()
 
 return wrapper
 
 def example():
 print("I'm a function!")
37. def decorator(func):
 def wrapper():
 print("I'm a wrapper.")
 func()
 
 return wrapper
 
 def example():
 print("I'm a function!")
38. >>> wrapped = decorator(example) >>> wrapped() I'm a wrapper. I'm a function! def decorator(func):
 def wrapper():
 print("I'm a wrapper.")
 func()
 
 return wrapper
 
 def example():
 print("I'm a function!")
39. >>> wrapped = decorator(example) >>> wrapped() I'm a wrapper. I'm a function!
40. >>> example = decorator(example) >>> example() I'm a wrapper. I'm a function! >>> wrapped = decorator(example) >>> wrapped() I'm a wrapper. I'm a function!
41. def decorator(f):
 def wrapper():
 print("I'm a wrapper.")
 f()
 
 return wrapper
 
 def example():
 print("I'm a function!") ! example = decorator(example)
42. def decorator(f):
 def wrapper():
 print("I'm a wrapper.")
 f()
 
 return wrapper
 
 def example():
 print("I'm a function!") ! example = decorator(example)
43. PEP 318
44. example = decorator(example)
45. example = decorator(example) example = decorator(example) @decorator
 def example():
 print("I'm a function!")
46. def get_user_profile():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 user = users.get(user_id)
 return jsonify(user=user.to_json())
47. def get_user_profile():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 user = users.get(user_id)
 return jsonify(user=user.to_json())
48. def login_required(func):
 def wrapper(*args, **kwargs):
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 return func(*args, **kwargs)
 
 return wrapper
49. @login_required
 def get_user_profile():
 user = users.get(session.get('user_id'))
 return jsonify(user=user.to_json()) def login_required(func):
 def wrapper(*args, **kwargs):
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 return func(*args, **kwargs)
 
 return wrapper
50. @login_required
 def get_user_profile():
 user = users.get(session.get('user_id'))
 return jsonify(user=user.to_json()) def login_required(func):
 def wrapper(*args, **kwargs):
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 return func(*args, **kwargs)
 
 return wrapper
51. def create_new_user():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 user = users.get(session.get('user_id'))
 if not user.has_role('admin'):
 abort(401)
 
 data = request.get_json()
 newbie = users.create(**data)
 return jsonify(user=newbie.to_json()), 201
52. def create_new_user():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 user = users.get(session.get('user_id'))
 if not user.has_role('admin'):
 abort(401)
 
 data = request.get_json()
 newbie = users.create(**data)
 return jsonify(user=newbie.to_json()), 201
53. @login_required def create_new_user(): user = users.get(session.get('user_id'))
 if not user.has_role('admin'):
 abort(401)
 
 data = request.get_json()
 newbie = users.create(**data)
 return jsonify(user=newbie.to_json()), 201
54. @login_required
 def create_new_user():
 user = users.get(session.get('user_id'))
 if not user.has_role('admin'):
 abort(401)
 
 data = request.get_json()
 newbie = users.create(**data)
 return jsonify(user=newbie.to_json()), 201
55. Remember...
56. @login_required
 def get_user_profile():
 # ... ...is the same as...
57. get_user_profile = login_required(get_user_profile) @login_required
 def get_user_profile():
 # ... ...is the same as...
58. @role_required('admin')
 def create_user():
 # ...
59. @role_required('admin')
 def create_user():
 # ... ...is the same as...
60. create_user = role_required('admin')(create_user) @role_required('admin')
 def create_user():
 # ... ...is the same as...
61. create_user = role_required('admin')(create_user) @role_required('admin')
 def create_user():
 # ... OR ...is the same as...
62. create_user = role_required('admin')(create_user) @role_required('admin')
 def create_user():
 # ... OR decorator = role_required('admin')
 create_user = decorator(create_user) ...is the same as...
63. def admin_required(func): 
 def wrapper(*args, **kwargs):
 user = users.get(session.get('user_id'))
 if not user.has_role('admin'):
 abort(401) 
 return func(*args, **kwargs)
 
 return wrapper
64. def admin_required():
 def decorator(func): 
 def wrapper(*args, **kwargs):
 user = users.get(session.get('user_id'))
 if not user.has_role('admin'):
 abort(401) return func(*args, **kwargs) 
 return wrapper
 return decorator
65. def role_required(role):
 def decorator(func): 
 def wrapper(*args, **kwargs):
 user = users.get(session.get('user_id'))
 if not user.has_role(role):
 abort(401)
 return func(*args, **kwargs) 
 return wrapper
 return decorator
66. @role_required('admin')
 def create_user():
 data = request.get_json()
 new_user = users.create(**data)
 return jsonify(user=new_user.to_json()), 201 def role_required(role):
 def decorator(func): 
 def wrapper(*args, **kwargs):
 user = users.get(session.get('user_id'))
 if not user.has_role(role):
 abort(401)
 return func(*args, **kwargs) 
 return wrapper
 return decorator
67. @login_required
 @role_required('admin')
 def create_user():
 data = request.get_json()
 new_user = users.create(**data)
 return jsonify(user=new_user.to_json()), 201
68. @login_required
 @role_required('admin')
 def create_user(): # ... ...is the same as...
69. @login_required
 @role_required('admin')
 def create_user(): # ... ...is the same as... create_user = login_required(role_required(‘admin’)(create_user))
70. @login_required
 @role_required('admin')
 def create_user():
 data = request.get_json()
 new_user = users.create(**data)
 return jsonify(user=new_user.to_json()), 201
72. @login_required
 def get_user_profile():
 # ... def login_required(func):
 def wrapper(*args, **kwargs):
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 return func(*args, **kwargs)
 
 return wrapper
73. @login_required
 def get_user_profile():
 # ... >>> get_user_profile.__name__ def login_required(func):
 def wrapper(*args, **kwargs):
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 return func(*args, **kwargs)
 
 return wrapper
74. @login_required
 def get_user_profile():
 # ... >>> get_user_profile.__name__ 'wrapper' def login_required(func):
 def wrapper(*args, **kwargs):
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 return func(*args, **kwargs)
 
 return wrapper
75. from functools import wraps
76. def login_required(func):
 def wrapper(*args, **kwargs):
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 return func(*args, **kwargs)
 
 return wrapper
77. from functools import wraps
 
 def login_required(func):
 @wraps(func)
 def wrapper(*args, **kwargs):
 user_id = session.get(user_id)
 if user_id is None:
 return redirect('/login', code=302)
 
 return func(*args, **kwargs)
 return wrapper
78. from functools import wraps
 
 def login_required(func):
 @wraps(func)
 def wrapper(*args, **kwargs):
 user_id = session.get(user_id)
 if user_id is None:
 return redirect('/login', code=302)
 
 return func(*args, **kwargs)
 return wrapper @login_required
 def get_user_profile():
 # ...
79. from functools import wraps
 
 def login_required(func):
 @wraps(func)
 def wrapper(*args, **kwargs):
 user_id = session.get(user_id)
 if user_id is None:
 return redirect('/login', code=302)
 
 return func(*args, **kwargs)
 return wrapper @login_required
 def get_user_profile():
 # ... >>> get_user_profile.__name__
80. from functools import wraps
 
 def login_required(func):
 @wraps(func)
 def wrapper(*args, **kwargs):
 user_id = session.get(user_id)
 if user_id is None:
 return redirect('/login', code=302)
 
 return func(*args, **kwargs)
 return wrapper @login_required
 def get_user_profile():
 # ... >>> get_user_profile.__name__ ‘get_user_profile’
81. Recap
82. def get_user_profile():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 user = users.get(user_id)
 return jsonify(user=user.to_json())
 
 
 def create_user():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 user = users.get(session.get('user_id'))
 if not user.has_role('admin'):
 abort(401)
 
 data = request.get_json()
 new_user = users.create(**data)
 return jsonify(user=new_user.to_json()), 201
83. def get_user_profile():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 user = users.get(user_id)
 return jsonify(user=user.to_json())
 
 
 def create_user():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 user = users.get(g.get('user_id'))
 if not user.has_role('admin'):
 abort(401)
 
 data = request.get_json()
 new_user = users.create(**data)
 return jsonify(user=new_user.to_json()), 201
84. def login_required(func):
 def wrapper(*args, **kwargs):
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 return func(*args, **kwargs)
 
 return wrapper def role_required(role):
 def decorator(func): 
 def wrapper(*args, **kwargs):
 user = users.get(session.get('user_id'))
 if not user.has_role(role):
 abort(401)
 return func(*args, **kwargs) 
 return wrapper
 return decorator
85. @login_required
 def get_user_profile():
 user = users.get(session.get(‘user_id'))
 return jsonify(user=user.to_json())
 
 
 @login_required
 @role_required('admin')
 def create_user():
 data = request.get_json()
 new_user = users.create(**data)
 return jsonify(user=new_user.to_json()), 201
87. Decorators
88. Questions? @epochblue Thank you.