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14_Day/14_higher_order_function.md
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@ -19,13 +19,13 @@
![30DaysOfPython](../images/30DaysOfPython_banner3@2x.png)
- [📘 Day 14](#%f0%9f%93%98-day-14)
- [Higher Order Functions](#higher-order-functions)
- [Function as a parameter](#function-as-a-parameter)
- [Function as a return value](#function-as-a-return-value)
- [Python closures](#python-closures)
- [Python decorators](#python-decorators)
- [Function as a Parameter](#function-as-a-parameter)
- [Function as a Return Value](#function-as-a-return-value)
- [Python Closures](#python-closures)
- [Python Decorators](#python-decorators)
- [Creating Decorators](#creating-decorators)
- [Applying Multiple Decorators to a Single Function](#applying-multiple-decorators-to-a-single-function)
- [Accepting parameters in Decorator Functions](#accepting-parameters-in-decorator-functions)
- [Accepting Parameters in Decorator Functions](#accepting-parameters-in-decorator-functions)
- [Built-in Higher Order Functions](#built-in-higher-order-functions)
- [Python - Map Function](#python---map-function)
- [Python - Filter Function](#python---filter-function)
@ -49,11 +49,11 @@ In this section, we will cover:
2. Returning functions as return value from other functions
3. Using python closures and decorators
### Function as a parameter
### Function as a Parameter
```py
def sum_numbers(nums): # normal function
return sum(nums)
return sum(nums) # a sad function abusing the built-in sum function :<
def higher_order_function(f, *args): # function as a parameter
summation = f(*args)
@ -62,7 +62,7 @@ result = higher_order_function(sum_numbers, [1, 2, 3, 4, 5])
print(result) # 15
```
### Function as a return value
### Function as a Return Value
```py
def square(x): # a square function
@ -72,14 +72,12 @@ def cube(x): # a cube function
return x ** 3
def absolute(x): # an absolute value function
if x == 0:
if x >= 0:
return x
elif x < 1:
return -(x)
else:
return x
return -(x)
def higher_order_function(type): # a higher order function returning function
def higher_order_function(type): # a higher order function returning a function
if type == 'square':
return square
elif type == 'cube':
@ -97,9 +95,9 @@ print(result(-3)) # 3
You can see from the above example that the higher order function is returning different functions depending on the passed parameter
## Python closures
## Python Closures
Python allows a nested function to access the outer scope of the enclosing function. This is is known as a Closure. Let’s have a look at how closures works in Python. In Python, closure is created by nesting a function inside another encapsulating function and then returning the inner function. See the example below.
Python allows a nested function to access the outer scope of the enclosing function. This is is known as a Closure. Let’s have a look at how closures work in Python. In Python, closure is created by nesting a function inside another encapsulating function and then returning the inner function. See the example below.
**Example:**
@ -116,13 +114,13 @@ print(closure_result(5)) # 15
print(closure_result(10)) # 20
```
## Python decorators
## Python Decorators
A decorator is a design pattern in Python that allows a user to add new functionality to an existing object without modifying its structure. Decorators are usually called before the definition of a function you want to decorate.
### Creating Decorators
To create a decorator function, we need an outer function, inner wrapper function.
To create a decorator function, we need an outer function with an inner wrapper function.
**Example:**
@ -139,10 +137,10 @@ def uppercase_decorator(function):
g = uppercase_decorator(greeting)
print(g()) # WELCOME TO PYTHON
## Lets implement the above to a decorator
## Lets implement the example above with a decorator
'''This decorator function is a higher order
which is take function as a parameter'''
'''This decorator function is a higher order function
that takes a function as a parameter'''
def uppercase_decorator(function):
def wrapper():
func = function()
@ -161,7 +159,7 @@ print(greeting()) # WELCOME TO PYTHON
```py
'''These decorator functions are higher order functions
which take function as parameters'''
that take functions as parameters'''
# First Decorator
def uppercase_decorator(function):
@ -179,15 +177,16 @@ def split_string_decorator(function):
return wrapper
@uppercase_decorator
@split_string_decorator
@uppercase_decorator # order with decorators is important in this case - .upper() function does not work with lists
def greeting():
return 'Welcome to Python'
print(greeting()) # WELCOME TO PYTHON
```
### Accepting parameters in Decorator Functions
### Accepting Parameters in Decorator Functions
Most of the time we need our functions to take parameters, so we might need to define a decorator that accepts parameters.
@ -200,7 +199,7 @@ def decorator_with_parameters(function):
@decorator_with_parameters
def print_full_name(first_name, last_name, country):
print("I am {} {}. I love teaching".format(
print("I am {} {}. I love to teach.".format(
first_name, last_name, country))
print_full_name("Asabeneh", "Yetayeh",'Finland')
@ -208,12 +207,12 @@ print_full_name("Asabeneh", "Yetayeh",'Finland')
## Built-in Higher Order Functions
Some of the builtin higher order function which we cover in the part are _map()_, _filter_, and _reduce_.
Lambda function can be passed a parameter and the best use case of lambda function is in function like map, filter and reduce.
Some of the built-in higher order functions that we cover in this part are _map()_, _filter_, and _reduce_.
Lambda function can be passed as a parameter and the best use case of lambda functions is in functions like map, filter and reduce.
### Python - Map Function
The map() function is a built-in function which takes a function and iterable as parameter.
The map() function is a built-in function that takes a function and iterable as parameters.
```py
# syntax
@ -257,11 +256,11 @@ names_upper_cased = map(lambda name: name.upper(), names)
print(list(names_upper_cased)) # ['ASABENEH', 'LIDIYA', 'ERMIAS', 'ABRAHAM']
```
What actually map do is mapping a list. For instance it changes the names to upper case and return a new list.
What actually map does is iterating over a list. For instance, it changes the names to upper case and returns a new list.
### Python - Filter Function
The filter() function calls the specified function which returns boolean for each item of the specified iterable (list). It filters the items which the satisfied with the filtering criteria.
The filter() function calls the specified function which returns boolean for each item of the specified iterable (list). It filters the items that satisfy the filtering criteria.
```py
# syntax
@ -311,7 +310,7 @@ print(list(long_names)) # ['Asabeneh']
### Python - Reduce Function
The _reduce()_ function is defined in the functools module and we should import it from this module.Like map and filter it takes two parameters, a function and an iterable. However, it doesn't return another iterable, instead it returns a single value.
The _reduce()_ function is defined in the functools module and we should import it from this module. Like map and filter it takes two parameters, a function and an iterable. However, it doesn't return another iterable, instead it returns a single value.
**Example:2**
@ -333,28 +332,27 @@ numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
```
1. Explain the difference between map, filter, and reduce.
1. Explain the difference between higher order function, closure and decorator
1. Define a call function before map, filter or reduce, see examples.
1. Use for loop to print each country in the countries list.
1. Use for to print each name in the names list.
1. Use for to print each number in the numbers list.
1. Use map to create a new list by changing each country to uppercase in the countries list
1. Use map to create a new list by changing each number to square in the numbers list
1. Use map to change to each name to uppercase in the names list
1. Use filter to filter out countries containing land.
1. Use filter to filter out countries having six character.
1. Use filter to filter out countries containing six letters and more in the country list.
1. Use filter to filter out country start with 'E'
1. Chain two or more list iterators(eg. arr.map(callback).filter(callback).reduce(callback))
1. Declare a function called get_string_lists which takes an list as a parameter and then returns an list only with string items.
1. Use reduce to sum all the numbers in the numbers list.
1. Use reduce to concatenate all the countries and to produce this sentence: Estonia, Finland, Sweden, Denmark, Norway, and IceLand are north European countries
1. Declare a function called categorize_countries which returns an list of countries which have some common pattern(you find the [countries list](https://github.com/Asabeneh/30-Days-Of-Python/blob/master/data/countries.py) in this repository as countries.js(eg 'land', 'ia', 'island', 'stan')).
1. Create a function which return a list of dictionary, which is the letter and the number of times the letter used to start a name of a country.
1. Declare a get_first_ten_countries function and return an list of ten countries from the countries.js list in the data folder.
1. Declare a get_last_ten_countries function which which returns the last ten countries in the countries list.
1. Find out which letter is used many times as initial for a country name from the [countries list](https://github.com/Asabeneh/30-Days-Of-Python/blob/master/data/countries-data.py)(eg. Finland, Fiji, France etc)
1. Use the countries_data.py file information, in the data folder.
2. Explain the difference between higher order function, closure and decorator
3. Define a call function before map, filter or reduce, see examples.
4. Use for loop to print each country in the countries list.
5. Use for to print each name in the names list.
6. Use for to print each number in the numbers list.
7. Use map to create a new list by changing each country to uppercase in the countries list
8. Use map to create a new list by changing each number to its square in the numbers list
9. Use map to change each name to uppercase in the names list
10. Use filter to filter out countries containing 'land'.
11. Use filter to filter out countries having exactly six characters.
12. Use filter to filter out countries containing six letters and more in the country list.
13. Use filter to filter out countries starting with an 'E'
14. Chain two or more list iterators (eg. arr.map(callback).filter(callback).reduce(callback))
15. Declare a function called get_string_lists which takes a list as a parameter and then returns a list containing only string items.
16. Use reduce to sum all the numbers in the numbers list.
17. Use reduce to concatenate all the countries and to produce this sentence: Estonia, Finland, Sweden, Denmark, Norway, and Iceland are north European countries
18. Declare a function called categorize_countries that returns a list of countries with some common pattern (you can find the [countries list](https://github.com/Asabeneh/30-Days-Of-Python/blob/master/data/countries.py) in this repository as countries.js(eg 'land', 'ia', 'island', 'stan')).
19. Create a function returning a dictionary, where keys stand for starting letters of countries and values are the number of country names starting with that letter.
20. Declare a get_first_ten_countries function - it returns a list of first ten countries from the countries.js list in the data folder.
21. Declare a get_last_ten_countries function that returns the last ten countries in the countries list.
23. Use the countries_data.py (https://github.com/Asabeneh/30-Days-Of-Python/blob/master/data/countries-data.py) file and follow the tasks below:
- Sort countries by name, by capital, by population
- Sort out the ten most spoken languages by location.
- Sort out the ten most populated countries.