Implementation of Closure
Let's consider the example of closure:
1234567891011121314151617def outer(argument): def inner(): nonlocal argument argument += 5 return argument return inner variable1 = outer(11) variable2 = outer(9) print("First variable1 returns", variable1()) print("Second variable1 returns", variable1()) print("First variable2 returns", variable2()) print("Second variable2 returns", variable2())
We can operate with the enclosed data: the nonlocal keyword provides the ability to change argument (similar to the global keyword).
Steps to create closure
Step 1:
Create the outer function with its local scope.
def outer():
a = 4
Step 2:
Create an inner function with local scope defined inside the outer function.
def outer():
a = 4
def inner():
Step 3:
Access the non-local (outer scope) data from within the inner local scope.
def outer():
a = 4
def inner():
nonlocal a
Step 4:
Return the inner function and assign it to the variable.
def outer():
a = 4
def inner():
nonlocal a
return inner
variable = outer()
Step 5:
The local scope of the outer function is removed once it has finished executing.
#def outer():
# a = 4
#
def inner():
nonlocal a
#
# return inner
variable = outer()
Step 6:
The inner function returned by the outer function is assigned to the variable and has an enclosing scope with data.
#def outer():
# a = 4
#
def inner():
nonlocal a
#
# return inner
variable = inner
variable() # is equal to inner()
The enclosing scope occupies less memory than the non-local scope because it contains only the dependent values. Enclosed variables/objects do not have names and are represented as memory addresses.
The closure and enclosing scope are commonly used in decorators.
Note
Every time the
outer()function is called, a newinner()function is defined.The returned
inner()functions are distinct and independent objects.
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Let's consider the example of closure:
1234567891011121314151617def outer(argument): def inner(): nonlocal argument argument += 5 return argument return inner variable1 = outer(11) variable2 = outer(9) print("First variable1 returns", variable1()) print("Second variable1 returns", variable1()) print("First variable2 returns", variable2()) print("Second variable2 returns", variable2())
We can operate with the enclosed data: the nonlocal keyword provides the ability to change argument (similar to the global keyword).
Steps to create closure
Step 1:
Create the outer function with its local scope.
def outer():
a = 4
Step 2:
Create an inner function with local scope defined inside the outer function.
def outer():
a = 4
def inner():
Step 3:
Access the non-local (outer scope) data from within the inner local scope.
def outer():
a = 4
def inner():
nonlocal a
Step 4:
Return the inner function and assign it to the variable.
def outer():
a = 4
def inner():
nonlocal a
return inner
variable = outer()
Step 5:
The local scope of the outer function is removed once it has finished executing.
#def outer():
# a = 4
#
def inner():
nonlocal a
#
# return inner
variable = outer()
Step 6:
The inner function returned by the outer function is assigned to the variable and has an enclosing scope with data.
#def outer():
# a = 4
#
def inner():
nonlocal a
#
# return inner
variable = inner
variable() # is equal to inner()
The enclosing scope occupies less memory than the non-local scope because it contains only the dependent values. Enclosed variables/objects do not have names and are represented as memory addresses.
The closure and enclosing scope are commonly used in decorators.
Note
Every time the
outer()function is called, a newinner()function is defined.The returned
inner()functions are distinct and independent objects.
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