Python Decorators: How Do You Even

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. @decorators pytn · february 7, 2015
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(403)
 
 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. What this talk is not
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())
 
 
 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(403)
 
 data = request.get_json()
 new_user = users.create(**data)
 return jsonify(user=new_user.to_json()), 201
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. 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())
11. But first...
12. Let’s talk about functions
13. def example():
 print("I'm a function!")
14. >>> example() I'm a function! def example():
 print("I'm a function!")
15. First-Class Functions
16. Save functions into variables
17. def example():
 print("I'm a function!")
18. def example():
 print("I'm a function!") >>> f = example >>> f() I'm a function!
19. Pass functions as arguments
20. def example():
 print("I'm a function!")
21. def example():
 print("I'm a function!") def first_class(func):
 func()
22. def example():
 print("I'm a function!") >>> first_class(example) I'm a function! def first_class(func):
 func()
23. Return functions from functions
24. def example():
 print("I'm a function!")
25. def example():
 print("I'm a function!") def first_class2():
 return example
26. def example():
 print("I'm a function!") >>> f = first_class2() >>> f() I'm a function! def first_class2():
 return example
27. Nest functions inside of functions
28. def first_class3():
 msg = "I'm a function!"
 
 def example():
 print(msg)
 
 example()
29. def first_class3():
 msg = "I'm a function!"
 
 def example():
 print(msg)
 
 example() >>> first_class3() I'm a function!
30. First-Class Functions
31. Save functions into variables
32. Return functions from functions Save functions into variables
33. Pass functions as arguments Save functions into variables Return functions from functions
34. Nest functions inside of functions Save functions into variables Pass functions as arguments Return functions from functions
35. Return functions from functions Pass functions as arguments Nest functions inside of functions Save functions into variables
36. Return functions from functions Pass functions as arguments Nest functions inside of functions Save functions into variables Decorators
37. def example():
 print("I'm a function!")
38. def decorator(func):
 def wrapper():
 print("I'm a wrapper.")
 func()
 
 return wrapper def example():
 print("I'm a function!")
39. def decorator(func):
 def wrapper():
 print("I'm a wrapper.")
 func()
 
 return wrapper def example():
 print("I'm a function!")
40. >>> 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!")
41. >>> wrapped = decorator(example) >>> wrapped() I'm a wrapper. I'm a function!
42. >>> wrapped = decorator(example) >>> wrapped() I'm a wrapper. I'm a function! >>> wrapped = decorator(example) >>> wrapped() I'm a wrapper. I'm a function!
43. >>> example = decorator(example) >>> example() I'm a wrapper. I'm a function! >>> wrapped = decorator(example) >>> wrapped() I'm a wrapper. I'm a function!
44. def decorator(f):
 def wrapper():
 print("I'm a wrapper.")
 f()
 
 return wrapper
 
 def example():
 print("I'm a function!") example = decorator(example)
45. def decorator(f):
 def wrapper():
 print("I'm a wrapper.")
 f()
 
 return wrapper
 
 def example():
 print("I'm a function!") example = decorator(example)
46. PEP 318
47. example = decorator(example)
48. example = decorator(example) example = decorator(example) @decorator
 def example():
 print("I'm a function!")
49. 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())
50. 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())
51. def decorator(func):
 def wrapper():
 print("I'm a wrapper.")
 
 func()
 
 return wrapper
52. def decorator(func):
 def wrapper():
 user_id = session.get('user_id')
 if user_id is None:
 return redirect('/login', code=302)
 
 func()
 
 return wrapper
53. 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
54. @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
55. @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
56. 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(403)
 
 data = request.get_json()
 newbie = users.create(**data)
 return jsonify(user=newbie.to_json()), 201
57. 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(403)
 
 data = request.get_json()
 newbie = users.create(**data)
 return jsonify(user=newbie.to_json()), 201
58. @login_required def create_new_user(): user = users.get(session.get('user_id'))
 if not user.has_role('admin'):
 abort(403)
 
 data = request.get_json()
 newbie = users.create(**data)
 return jsonify(user=newbie.to_json()), 201
59. @login_required
 def create_new_user():
 user = users.get(session.get('user_id'))
 if not user.has_role('admin'):
 abort(403)
 
 data = request.get_json()
 newbie = users.create(**data)
 return jsonify(user=newbie.to_json()), 201
60. Remember...
61. @login_required
 def get_user_profile():
 # ... ...is the same as...
62. get_user_profile = login_required(get_user_profile) @login_required
 def get_user_profile():
 # ... ...is the same as...
63. @role_required('admin')
 def create_user():
 # ...
64. @role_required('admin')
 def create_user():
 # ... ...is the same as...
65. create_user = role_required('admin')(create_user) @role_required('admin')
 def create_user():
 # ... ...is the same as...
66. create_user = role_required('admin')(create_user) @role_required('admin')
 def create_user():
 # ... OR ...is the same as...
67. 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...
68. def admin_required(func): 
 def wrapper(*args, **kwargs):
 user = users.get(session.get('user_id'))
 if not user.has_role('admin'):
 abort(403) 
 return func(*args, **kwargs)
 
 return wrapper
69. def admin_required():
 def decorator(func): 
 def wrapper(*args, **kwargs):
 user = users.get(session.get('user_id'))
 if not user.has_role('admin'):
 abort(403) return func(*args, **kwargs) 
 return wrapper
 return decorator
70. 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(403)
 return func(*args, **kwargs) 
 return wrapper
 return decorator
71. @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 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(403)
 return func(*args, **kwargs) 
 return wrapper
 return decorator
72. @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 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(403)
 return func(*args, **kwargs) 
 return wrapper
 return decorator
73. @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
74. @login_required
 @role_required('admin')
 def create_user(): # ... ...is the same as...
75. @login_required
 @role_required('admin')
 def create_user(): # ... ...is the same as... create_user = login_required( role_required('admin')(create_user) )
76. @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
78. @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
79. @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
80. @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
81. from functools import wraps
82. 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
83. 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
84. 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():
 # ...
85. 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__
86. 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’
87. Recap
88. 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(403)
 
 data = request.get_json()
 new_user = users.create(**data)
 return jsonify(user=new_user.to_json()), 201
89. 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(403)
 
 data = request.get_json()
 new_user = users.create(**data)
 return jsonify(user=new_user.to_json()), 201
90. 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(403)
 return func(*args, **kwargs) 
 return wrapper
 return decorator
91. @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
92. Decorators
93. Decorators @epochblue Questions? thank you!