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
   

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3. @epochblue
   

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4. @epochblue
   

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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
   

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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
   

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7. What this talk
   is not
   

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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
   

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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())
   

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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())
    

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11. But
    first...
    

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12. Let’s talk
    about functions
    

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13. def example():

    print("I'm a function!")
    

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14. >>> example()
    I'm a function!
    def example():

    print("I'm a function!")
    

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15. First-Class
    Functions
    

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16. Save functions
    into variables
    

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17. def example():

    print("I'm a function!")
    

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18. def example():

    print("I'm a function!")
    >>> f = example
    >>> f()
    I'm a function!
    

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19. Pass functions
    as arguments
    

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20. def example():

    print("I'm a function!")
    

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21. def example():

    print("I'm a function!")
    def first_class(func):

    func()
    

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22. def example():

    print("I'm a function!")
    >>> first_class(example)
    I'm a function!
    def first_class(func):

    func()
    

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23. Return functions
    from functions
    

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24. def example():

    print("I'm a function!")
    

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25. def example():

    print("I'm a function!")
    def first_class2():

    return example
    

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26. def example():

    print("I'm a function!")
    >>> f = first_class2()
    >>> f()
    I'm a function!
    def first_class2():

    return example
    

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27. Nest functions
    inside of
    functions
    

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28. def first_class3():

    msg = "I'm a function!"

    

    def example():

    print(msg)

    

    example()
    

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29. def first_class3():

    msg = "I'm a function!"

    

    def example():

    print(msg)

    

    example()
    >>> first_class3()
    I'm a function!
    

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30. First-Class
    Functions
    

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31. Save functions
    into variables
    

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32. Return
    functions from
    functions
    Save functions
    into variables
    

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33. Pass functions
    as arguments
    Save functions
    into variables
    Return functions
    from functions
    

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34. Nest functions
    inside of
    functions
    Save functions
    into variables
    Pass functions
    as arguments
    Return functions
    from functions
    

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35. Return functions
    from functions
    Pass functions
    as arguments
    Nest functions
    inside of functions
    Save functions
    into variables
    

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36. Return functions
    from functions
    Pass functions
    as arguments
    Nest functions
    inside of functions
    Save functions
    into variables
    Decorators
    

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37. def example():

    print("I'm a function!")
    

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38. def decorator(func):

    def wrapper():

    print("I'm a wrapper.")

    func()

    

    return wrapper
    def example():

    print("I'm a function!")
    

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39. def decorator(func):

    def wrapper():

    print("I'm a wrapper.")

    func()

    

    return wrapper
    def example():

    print("I'm a function!")
    

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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!")
    

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41. >>> wrapped = decorator(example)
    >>> wrapped()
    I'm a wrapper.
    I'm a function!
    

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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!
    

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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!
    

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44. def decorator(f):

    def wrapper():

    print("I'm a wrapper.")

    f()

    

    return wrapper

    

    def example():

    print("I'm a function!")
    example = decorator(example)
    

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45. def decorator(f):

    def wrapper():

    print("I'm a wrapper.")

    f()

    

    return wrapper

    

    def example():

    print("I'm a function!")
    example = decorator(example)
    
    

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46. PEP 318
    

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47. example = decorator(example)
    

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48. example = decorator(example)
    example = decorator(example)
    @decorator

    def example():

    print("I'm a function!")
    

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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())
    

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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())
    

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51. def decorator(func):

    def wrapper():

    print("I'm a wrapper.")

    

    func()

    

    return wrapper
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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60. Remember...
    

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61. @login_required

    def get_user_profile():

    # ...
    ...is the same as...
    

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62. get_user_profile = login_required(get_user_profile)
    @login_required

    def get_user_profile():

    # ...
    ...is the same as...
    

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63. @role_required('admin')

    def create_user():

    # ...
    

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64. @role_required('admin')

    def create_user():

    # ...
    ...is the same as...
    

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65. create_user = role_required('admin')(create_user)
    @role_required('admin')

    def create_user():

    # ...
    ...is the same as...
    

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66. create_user = role_required('admin')(create_user)
    @role_required('admin')

    def create_user():

    # ...
    OR
    ...is the same as...
    

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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...
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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74. @login_required

    @role_required('admin')

    def create_user():
    # ...
    ...is the same as...
    

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75. @login_required

    @role_required('admin')

    def create_user():
    # ...
    ...is the same as...
    create_user = login_required(
    role_required('admin')(create_user)
    )
    

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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
    

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77. View Slide

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
    

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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
    

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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
    

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81. from functools import wraps
    

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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
    

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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
    

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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():

    # ...
    

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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__
    

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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’
    

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87. Recap
    

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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
    

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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
    

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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
    

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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
    

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92. Decorators
    

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93. Decorators
    @epochblue
    Questions?
    thank you!
    

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