Python basics_ part1

Python Basics
Eng.Elaf Ahmed Saeed

What is Python?
Python is a popular programming language. It was created by Guido van
Rossum, and released in 1991.
It is used for:
• web development (server-side),
• software development,
• mathematics,
• system scripting.

What can Python do?
• Python can be used on a server to create web applications.
• Python can be used alongside software to create workflows.
• Python can connect to database systems. It can also read and modify files.
• Python can be used to handle big data and perform complex mathematics.
• Python can be used for rapid prototyping, or for production-ready software
development.

Why Python?
• Python works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc).
• Python has a simple syntax similar to the English language.
• Python has syntax that allows developers to write programs with fewer lines than
some other programming languages.
• Python runs on an interpreter system, meaning that code can be executed as soon
as it is written. This means that prototyping can be very quick.
• Python can be treated in a procedural way, an object-oriented way or a functional way.

Python Install
• Many PCs and Macs will have python already installed.
• To check if you have python installed on a Windows PC, search in the start bar
for Python or run the following on the Command Line (cmd.exe):
C:UsersYour Name>python –version
• If you find that you do not have python installed on your computer, then you
can download it for free from the following website: https://www.python.org/

Python Quickstart
• Python is an interpreted programming language, this means that as a developer
you write Python (.py) files in a text editor and then put those files into the
python interpreter to be executed.
• The way to run a python file is like this on the command line:
C:UsersYour Name>python helloworld.py
• Where "helloworld.py" is the name of your python file.

Python Quickstart
• helloworld.py, which can be done in any text editor:
print("Hello, World!")
 result: Hello, World!

The Python Command Line
• To test a short amount of code in python sometimes it is quickest and easiest
not to write the code in a file. This is made possible because Python can be run
as a command line itself.
• Type the following on the Windows, Mac or Linux command line:
C:UsersYour Name>python
• Or, if the "python" command did not work, you can try "py":
C:UsersYour Name>py

• Example 1:
Result: Hello, World!

• Comments can be used to explain Python code.
• Comments can be used to make the code more readable.
• Comments can be used to prevent execution when testing code.

• Single Line Comments
Comments starts with a #, and Python will ignore them:
Example1:
#This is a comment
Example2:
print("Hello, World!") #This is a comment

• Multi Line Comments
Example1:
#This is a comment
#written in
#more than just one line

• Multi Line Comments
Example2:
"""
This is a comment
written in
more than just one line
"""

Creating Variables
• Variables are containers for storing data values.
• Unlike other programming languages, Python has no command for declaring a variable.
• A variable is created the moment you first assign a value to it.
• Example:
x = 5
y = "John"
print(x)
print(y)

Variable Names
A variable can have a short name (like x and y) or a more descriptive name (age, carname,
total_volume). Rules for Python variables:
• A variable name must start with a letter or the underscore character
• A variable name cannot start with a number
• A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
• Variable names are case-sensitive (age, Age and AGE are three different variables)

Variable Names
Example:
#Legal variable names:
myvar = "John"
my_var = "John"
_my_var = "John"
myVar = "John"
MYVAR = "John"
myvar2 = "John"
#Illegal variable names:
2myvar = "John"
my-var = "John"
my var = "John"

Assign Value to Multiple Variables
Python allows you to assign values to multiple variables in one line:
Example
x, y, z = "Orange", "Banana", "Cherry"
print(x)
print(y)
print(z)

Assign Value to Multiple Variables
And you can assign the same value to multiple variables in one line:
Example
x = y = z = "Orange"
print(x)
print(y)
print(z)

Output Variables
The Python print statement is often used to output variables.
To combine both text and a variable, Python uses the + character:
Example:
x = "awesome"
print("Python is " + x)

Output Variables
You can also use the + character to add a variable to another variable:
Example:
x = "Python is "
y = "awesome"
z = x + y
print(z)

Output Variables
For numbers, the + character works as a mathematical operator:
Example:
x = 5
y = 10
print(x + y)

Output Variables
If you try to combine a string and a number, Python will give you an error:
Example:
x = 5
y = "John"
print(x + y)

Global Variables
• Variables that are created outside of a function (as in all of the examples above) are known as global
variables.
• Global variables can be used by everyone, both inside of functions and outside.
Example
Create a variable outside of a function, and use it inside the function
x = "awesome"
def myfunc():
myfunc()

Global Variables
Example
Create a variable inside a function, with the same name as the global variable
x = "awesome"
def myfunc():
x = "fantastic"
myfunc()
Result:
Python is fantastic
Python is awesome

The global Keyword
Example
If you use the global keyword, the variable belongs to the global scope:
def myfunc():
global x
x = "fantastic"
myfunc()
Result:
Python is fantastic

The global Keyword
Example
To change the value of a global variable inside a function, refer to the variable by using the global
keyword:
x = "awesome"
def myfunc():
global x
x = "fantastic"
myfunc()
Result:
Python is fantastic

Built-in Data Types
In programming, data type is an important concept.
Variables can store data of different types, and different types can do different things.
Python has the following data types built-in by default, in these categories:
Text Type: str
Numeric Types: int, float, complex
Sequence Types: list, tuple, range
Mapping Type: dict
Set Types: set, frozenset
Boolean Type: bool
Binary Types: bytes, bytearray, memoryview

Getting the Data Type
You can get the data type of any object by using the type() function:
Example
Print the data type of the variable x:
x = 5
print(type(x))
Result:
<class 'int'>

Python Numbers
There are three numeric types in Python:
• int
• float
• Complex
Variables of numeric types are created when you assign a value to them:
Example
x = 1 # int
y = 2.8 # float
z = 1j # complex

Python Numbers
To verify the type of any object in Python, use the type() function:
Example
Result:
<class 'int'>
<class 'float'>
<class 'complex'>

Python Numbers
Int
Int, or integer, is a whole number, positive or negative, without decimals, of unlimited length.
Example
Result:
<class 'int'>
<class 'int'>
<class 'int'>

Python Numbers
Float
Float, or "floating point number" is a number, positive or negative, containing one or more
decimals.
Example
Result:
<class 'float'>
<class 'float'>
<class 'float'>

Python Numbers
Complex
Complex numbers are written with a "j" as the imaginary part:
Example
Result:
<class 'complex'>
<class 'complex'>
<class 'complex'>

Python Numbers
Type Conversion
You can convert from one type to another with the int(), float(), and complex() methods:
Example
Result:
1.0
2
(1+0j)
<class 'float'>
<class 'int'>
<class 'complex'>

Python Numbers
Note: You cannot convert complex numbers into another number type.
Random Number
Python does not have a random() function to make a random number, but Python has a built-in
module called random that can be used to make random numbers:
Example
Result:
1.0
2
(1+0j)
<class 'float'>
<class 'int'>
<class 'complex'>

Python Numbers
Example
Result:
1

Eng. Elaf Ahmed Saeed
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