Slides from the training on the topic "Python Programming Essentials"

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/SkillbrewTalent brewed by the
industry itself
Decorators
Pavan Verma
@YinYangPavan
Founder, P3 InfoTech Solutions Pvt. Ltd.
Python Programming Essentials

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What is a decorator?
 A decorator is a callable that takes a
function as an argument and returns a
replacement function
 Useful to wrap new capabilities inside a
function

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Decorator examples
@classmethod
@staticmethod
@property
@login_required

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Creating a decorator – our objective
>>> @logger
... def foo1(x, y=1):
... return x * y
>>> foo1(5, 4)
Arguments were: (5, 4), {}
20
>>> foo1(1)
Arguments were: (1,), {}
1

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Nested functions
>>> def outer():
... x = 1
... def inner():
... print x # 1
... inner() # 2
...
>>> outer()
1

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Functions are first class objects
# all objects in Python inherit from a common
baseclass
>>> issubclass(int, object)
True
>>> def foo():
... pass
>>> foo.__class__
<type 'function'>
>>> issubclass(foo.__class__, object)
True

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Functions can be passed as arguments
>>> def add(x, y):
... return x + y
>>> def sub(x, y):
... return x - y
>>> def apply(func, x, y):
... return func(x, y)
>>> apply(add, 2, 1)
3
>>> apply(sub, 2, 1)
1

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Functions can be returned from other functions
>>> def outer():
... def inner():
... print "Inside inner"
... return inner
...
>>> foo = outer()
>>> foo
<function inner at 0x...>
>>> foo()
Inside inner

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Function closures
>>> def outer():
... x = 1
... def inner():
... print x
... return inner
>>> foo = outer()
>>> foo.func_closure
(<cell at 0x...: int object at 0x...>,)

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Function closures (2)
>>> def outer(x):
... def inner():
... print x # 1
... return inner
>>> print1 = outer(1)
>>> print2 = outer(2)
>>> print1()
1
>>> print2()
2

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Simple decorator
>>> def outer(some_func):
... def inner():
... print "before some_func"
... ret = some_func()
... return ret + 1
... return inner
>>> def foo():
... return 1
>>> decorated = outer(foo)
>>> decorated()
before some_func
2

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Logger decorator
>>> def logger(func):
... def inner(*args, **kwargs):
... print "Arguments were: %s, %s" % (args,
kwargs)
... return func(*args, **kwargs)
... return inner

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Logger decorator usage
>>> @logger
... def foo1(x, y=1):
... return x * y
>>> @logger
... def foo2():
... return 2

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Logger decorator usage (2)
>>> foo1(5, 4)
Arguments were: (5, 4), {}
20
>>> foo1(1)
Arguments were: (1,), {}
1
>>> foo2() Arguments were: (), {}
2

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References
 http://simeonfranklin.com/blog/2012/jul/1/p
ython-decorators-in-12-steps/