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Python Basics 102- Python Functions.

Preston — Mon, 02 Aug 2021 09:23:54 +0000

In the previous post I introduced you to Python programming language, python installation and python fundamentals.
In this post we will go through Python functions

FUNCTIONS IN PYTHON

A function is a block of organized, reusable code that is used to perform a single, related action.
Functions minimize the repetition of code, hence they are reusable.
Below are the rules to define a function in Python.

Function blocks begin with the keyword def followed by the function name and parentheses ( ( ) ).
Any input parameters or arguments should be placed within these parentheses. You can also define parameters inside these parentheses.
In the body start with a """docstring""", to explain what the function does.
The code block within every function starts with a colon (:) and is indented. Check Pep 8
The statement return [expression] exits a function, optionally passing back an expression to the caller. A return statement with no arguments is the same as return None.

Function syntax

def functionname( parameters ):
   "function_docstring"
   function_suite
   return [expression]

Function Example

# define a function that says Hello World.
def greet():
    print("Hello World")

#calling the function
greet()
#prints> Hello World

Calling a Function

When you want to use a function, you just need to call it. A function call instructs Python to execute the code inside the function.

Returning a value

A function can perform a task like the greet() function. Or it can return a value. The value that a function returns is called a return value.
To return a value from a function, you use the return statement inside the function body.

Python Parameters and Arguments

It’s important to distinguish between the parameters and arguments of a function.

A parameter is a piece of information that a function needs. And you specify the parameter in the function definition.
An argument is a piece of data that you pass into the function.

Here is an Example to help us differentiate a parameter and an argument.

def sum(a, b):
    return a + b


total = sum(10,20)
print(total)

In this example, the sum() function has two parameters a and b, and returns the sum of them.
In the following function call, a will be 10 and b will be 20 inside the function body. These values 10 and 20 are called arguments.

Python Decorator.

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.

Syntax for a python decorator

from fastapi import FastAPI

app = FastAPI()

#Here is the decorator 
@app.get("/")
async def root():
    return {"message": "Hello World"}

Python Recursive Functions

A recursive function is a function that calls itself and always has condition that stops calling itself.

Python recursive function examples

1.Count Down to Zero
Suppose you need to develop a countdown function that counts down from a specified number to zero.
The following defines the count_down() function:

def count_down(start):
    """ Count down from a number  """
    print(start)

Example

def count_down(start):
    """ Count down from a number  """
    print(start)

    # call the count_down if the next
    # number is greater than 0
    next = start - 1
    if next > 0:
        count_down(next)


count_down(3)

Output:

3
2
1

Using a recursive function to calculate the sum of a sequence

Suppose that you need to calculate a sum of a sequence e.g., from 1 to 100. A simple way to do this is to use a for loop with the range() function:

def sum(n):
    total = 0
    for index in range(n+1):
        total += index

    return total


result = sum(100)
print(result)

Output:

Python Lambda Expressions

Lambda Function, also referred to as 'Anonymous function' is same as a regular python function but can be defined without a name. While normal functions are defined using the def keyword, anonymous functions are defined using the lambda keyword.

lambda expression syntax:

lambda arguments: expression

Lambda functions can have any number of arguments but only one expression. The expression is evaluated and returned. Lambda functions can be used wherever function objects are required.

Example:

double = lambda x: x * 2

print(double(5))

#sum of numbers
sum = lambda x: x+5
print(sum(5))
#> 5+5= 10

#multiple args
product = lambda x, y: x*y
print(product(5, 10))
#> 5*10 = 50

I hope this was helpful. Let's engage in a discussion on anything that I should add to make this article better.
Stay safe
Mask up
Coders gonna code!

Python 101-Introduction to Python

Preston — Sat, 24 Jul 2021 21:52:17 +0000

Python is a high-level, general-purpose, interpreted programming language.
Python is a general-purpose language. It means that you can use Python in various domains including: Web applications, Desktop software, mobile apps, Data science, machine learning, and AI.

Python programs have the extension .py and can be run from the command line by typing python file_name.py.

Install Python on Windows

First, download the latest version of Python from the download page.

Second, double-click the installer file to launch the setup wizard.

In the setup window, you need to check the Add Python 3.8 to PATH and click the Install Now to begin the installation.

Python Hello World

First, create a new folder called helloworld.

Second, launch the VS code and open the helloworld folder.

Third, create a new app.py file and enter the following code and save the file:

print('Hello, World!')

The print() is a built-in function that displays a message on the screen. In this example, it’ll show the message 'Hello, Word!'.

Python Basics

Section 1. Fundamentals

Python Variables

A variable is a label that you can assign a value to it. The value of a variable can change throughout the program.
Use the variable_name = value to create a variable.
The variable names should be as concise and descriptive as possible. Also, they should adhere to Python variable naming rules.

message = 'Hello, World!'
print(message)

In this example, message is a variable. It holds the string 'Hello, World!'. The print() function shows the message Hello, World! to the screen.

Python String

A string is a series of characters. In Python, anything inside quotes is a string. And you can use either single quotes or double-quotes. For example:

message = 'This is a string in Python'
message = "This is also a string"
#multiline string
help_message = '''
Usage: mysql command
    -h hostname     
    -d database name
    -u username
    -p password 
'''

Python Numbers

Python supports common numeric types including integers, floats, and complex numbers.

age = 10 # int
pi = 3.14 # float
total = age + pi # float
print(type(age), type(pi), type(total)) # <class 'int'> <class 'float'> <class 'float'>

Python Boolean

Python boolean data type has two values: True and False.

a = True
b = False
if a is True and b is False:
  print("Okay")

Section 2. Operators

Comparison, Logical, and Conditional Operators.

Comparison: ==, !=, <, >, <=, >=
Logical: and, or, not
Conditionals: if, else, elif

Section 3. Control flow

For Loops

Use the for loop statement to run a code block a fixed number of times.

for index in range(5):
    print(index)

Section 4. Functions

Python Functions

A Python function is a reusable named block of code that performs a task or returns a value.
Use the def keyword to define a new function. A function consists of function definition and body.

def greet(name):
    return f"Hi {name}"
greeting = greet('John')
print(greeting)
#multiple parameters
def sum(a, b):
    return a + b


total = sum(10,20)
print(total)

Section 5. Lists

Python Lists

A list is an ordered collection of items.
Python uses the square brackets ([]) to indicate a list. The following shows an empty list:

#list of numbers
numbers = [1, 3, 2, 7, 9, 4]
print(numbers)
#list of strings
colors = ['red', 'green', 'blue']
print(colors)
#Accessing elements in a list
numbers = [1, 3, 2, 7, 9, 4]
print(numbers[1])
#Adding elements in a list
numbers = [1, 3, 2, 7, 9, 4]
numbers.append(100)

print(numbers)
#Inserting elements to a list
numbers = [1, 3, 2, 7, 9, 4]
numbers.insert(2, 100)

print(numbers)
#Removing elements from a list
numbers = [1, 3, 2, 7, 9, 4]
del numbers[0]

print(numbers)

numbers = [1, 3, 2, 7, 9, 4]
last = numbers.pop()

print(last)
print(numbers)

Python Tuples

Tuples are immutable lists.
Use tuples when you want to define a list that cannot change.
A tuple is like a list except that it uses parentheses () instead of square brackets [].

rgb = ('red', 'green', 'blue')
print(rgb)

Section 6. Dictionaries

Python Dictionaries

A Python dictionary is a collection of key-value pairs, where each key has an associated value.
They are surrounded by {} and the value can have any data type.

person = {
    'first_name': 'John',
    'last_name': 'Doe',
    'age': 25,
    'favorite_colors': ['blue', 'green'],
    'active': True
}
print(person['first_name'])
print(person['last_name'])