Python Inner Functions
Last Updated :
25 Nov, 2019
In Python, functions are treated as first class objects. First class objects in a language are handled uniformly throughout. They may be stored in data structures, passed as arguments, or used in control structures. A programming language is said to support first-class functions if it treats functions as first-class objects. Python supports the concept of First Class functions.
Properties of first class functions:
- A function is an instance of the Object type.
- You can store the function in a variable.
- You can pass the function as a parameter to another function.
- You can return the function from a function.
- You can store them in data structures such as hash tables, lists, …
Note: To know more about first class objects click here.
Inner functions
A function which is defined inside another function is known as inner function or nested function. Nested functions are able to access variables of the enclosing scope. Inner functions are used so that they can be protected from everything happening outside the function. This process is also known as Encapsulation. To know more about encapsulation click here.
Example:
def outerFunction(text):
text = text
def innerFunction():
print(text)
innerFunction()
if __name__ == '__main__':
outerFunction('Hey !')
|
Output:
Hey!
In the above example, innerFunction() has been defined inside outerFunction(), making it an inner function. To call innerFunction(), we must first call outerFunction(). The outerFunction() will then go ahead and call innerFunction() as it has been defined inside it.
It is important that outer function has to be called, so that the inner function can execute. To demonstrate this consider the below example:
Example:
def outerFunction(text):
text = text
def innerFunction():
print(text)
innerFunction()
|
Output:
This code will return nothing when executed.
Scope of variable in nested function
The location where we can find a variable and also access it if required is called the scope of a variable.
It is known how to access a global variable inside a function, but, what about accessing the variable of an outer function? Let’s see an example:
def f1():
s = 'I love GeeksforGeeks'
def f2():
print(s)
f2()
f1()
|
Output:
I love GeeksforGeeks
In the above example, it can be seen that it is similar to accessing the global variable from a function. Now let’s suppose you want to change the variable of the outer function.
def f1():
s = 'I love GeeksforGeeks'
def f2():
s = 'Me too'
print(s)
f2()
print(s)
f1()
|
Output:
Me too
I love GeeksforGeeks
It can be seen the value of the variable of the outer function is not changed. However, the value of the variable of the outer function can be changed. There are different ways to change the value of the variable of the outer function.
- Using an iterable –
def f1():
s = ['I love GeeksforGeeks']
def f2():
s[0] = 'Me too'
print(s)
f2()
print(s)
f1()
|
Output:
['Me too']
['Me too']
- Using nonlocal keyword –
def f1():
s = 'I love GeeksforGeeks'
def f2():
nonlocal s
s = 'Me too'
print(s)
f2()
print(s)
f1()
|
Output:
Me too
Me too
- Value can also be changed as shown in the below example.
def f1():
f1.s = 'I love GeeksforGeeks'
def f2():
f1.s = 'Me too'
print(f1.s)
f2()
print(f1.s)
f1()
|
Output:
Me too
Me too
Python Closures
A Closure is a function object that remembers values in enclosing scopes even if they are not present in memory.
- It is a record that stores a function together with an environment: a mapping associating each free variable of the function (variables that are used locally, but defined in an enclosing scope) with the value or reference to which the name was bound when the closure was created.
- A closure—unlike a plain function—allows the function to access those captured variables through the closure’s copies of their values or references, even when the function is invoked outside their scope.
filter_none.
def outerFunction(text):
text = text
def innerFunction():
print(text)
return innerFunction
if __name__ == '__main__':
myFunction = outerFunction('Hey !')
myFunction()
|
Output:
Hey!
- As observed from above code, closures help to invoke function outside their scope.
- The function innerFunction has its scope only inside the outerFunction. But with the use of closures we can easily extend its scope to invoke a function outside its scope.
import logging
logging.basicConfig(filename ='example.log', level = logging.INFO)
def logger(func):
def log_func(*args):
logging.info(
'Running "{}" with arguments {}'.format(func.__name__, args))
print(func(*args))
return log_func
def add(x, y):
return x + y
def sub(x, y):
return x-y
add_logger = logger(add)
sub_logger = logger(sub)
add_logger(3, 3)
add_logger(4, 5)
sub_logger(10, 5)
sub_logger(20, 10)
|
Output:
6
9
5
10
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