1. In Python, we can define a function **inside** another function.
2. In Python, a function can be **passed as parameter** to another function
3. In Python, a function can also **return another function**

```
# A Python program to demonstrate that a function
# can be defined inside another function and a
# function can be passed as parameter.

# Adds a welcome message to the string
def messageWithWelcome(str):

    # Nested function
    def addWelcome():
        return "Welcome to "

    # Return concatenation of addWelcome()
    # and str.
    return  addWelcome() + str

# To get site name to which welcome is added
def site(site_name):
    return site_name

print messageWithWelcome(site("GeeksforGeeks"))
```
Output:
```
Welcome to GeeksforGeeks
```