everything_is_object.py

"""
You can assign functions to variables, store them in data structures,
pass them as arguments to other functions,
and even return them as values from other functions.
"""


def yell(text):
    return text.upper() + "!"


print(yell("Hello"))
# assign to a variable
"""
This line doesn’t call the function.
It takes the function object referenced by yell and creates a second name,
bark, that points to it.
"""
bark = yell
print(bark("woof"))
"""
You can delete the function’s original name (yell). Since
another name (bark) still points to the underlying function
"""
del yell
try:
    print(yell("Hello"))
except Exception as err:
    print("yell function is deleted")
print(bark("woof"))
# Python attaches a string identifier to every function at
# creation time for debugging purposes.
print(bark.__name__)
# Functions Can Be Stored in Data Structures
funcs = [bark, str.lower, str.capitalize]
for f in funcs:
    print(f, f("Hey there !"))


# Functions can be passed to other functions.
def greet(func):
    greeting = func("Hi, I am a Python program")
    print(greeting)


greet(bark)
# Functions that can accept other functions as arguments are also called higher-order functions.
# map function
high_list = list(map(bark, ["Hello", "hey", "hi"]))
print(high_list)


# Functions Can Be Nested
def speak(text):
    print(text)

    # inner function
    def whisper(text):
        if text == "Hello":
            print("Hi")
        else:
            print("Hello")

    # inner function call
    whisper(text)


speak("Hi")


# Functions Can Capture Local State
def make_adder(n):

    def add(x):
        return x + n

    return add


plus_3 = make_adder(3)
print(plus_3(4))  # expected -> 3 + 3