Python 101-Introduction to Python
Tags: python, programming
Published: 2021-07-24 21:52:17

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.

![image](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/pga0r1ri38iodq4nnea6.png)
##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:
```python
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.
```python
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:
```python
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.
```python
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.
```python
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.
```python
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.
```python
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:
```python
#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 [].
```python
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.
```python
person = {
    'first_name': 'John',
    'last_name': 'Doe',
    'age': 25,
    'favorite_colors': ['blue', 'green'],
    'active': True
}
print(person['first_name'])
print(person['last_name'])
```