Python Advanced - Modifying External Variables Used in Closures

External Variables Introduction:

Modify external variables used inside the closure

1. External Variables .Modify the external variables used in the closure

Bad example for modifying an external variable used inside a closure:
# define an external function
def func_out (num1):
# define an inner function
def func_inner (num2):
# The original intention here is to modify the value of the external num1, in fact, a local variable num1 is defined in the internal function
num1 = 10
# The inner function uses the outer function's variable (num1)
result = num1 + num2
print("The result is: ", result)
print(num1)
func_inner ( 1 )
print(num1)
# The outer function returns the inner function, and the inner function returned here is the closure
return func_inner
# create the closure instance
f = func_out ( 1 )
# execute the closure
f( 2)
Bad example for modifying an external variable used inside a closure:
# define an external function
def func_out (num1):
# define an inner function
def func_inner (num2):
# The original intention here is to modify the value of the external num1, in fact, a local variable num1 is defined in the internal function
nonlocal num1 # Tell the interpreter that the external variable a is used here
# Modify the external variable num1
num1 = 10
# The inner function uses the outer function's variable (num1)
result = num1 + num2
print("The result is: ", result)
print(num1)
func_inner ( 1 )
print(num1)
# The outer function returns the inner function, and the inner function returned here is the closure
return func_inner
# create the closure instance
f = func_out ( 1 )
# execute the closure
f( 2)

2. External Variables Summary

•Modifying external function variables used inside a closure is done using the nonlocal keyword.