Python Basics

Python
a programming language.
CLASS 1

What is Python?
 Python is a popular programming language.
 It was created in 1991 by Guido van Rossum.
 It is used for:
 web development (server-side),
 software development,
 mathematics,
 system scripting.
 Python can connect to database systems.

Python (cont...)
 Python works on different platforms
 Windows, Mac, Linux, Raspberry Pi, etc.
 Python has a simple syntax
 Python runs on an interpreter system
 meaning that, code can be executed as soon as it is written.
 Python can be treated in
 a procedural way,
 an object-orientated way,
 a functional way.

Python Syntax
 Python was designed for readability.
 Python uses new lines to complete a command
 as opposed to other programming languages which often use semicolons or parentheses.
 Python relies on indentation, using whitespace, to define scope; such as the scope
of loops, functions and classes.
 Other programming languages often use curly-brackets for this purpose.

Install python
 You can do it your own right?

Hello, World!
 print(“Hello, World!”)
 In terminal – command line.
 In file (saving with the extension “.py”).

Towards Programming
 In Python, the indentation is very important.
 Python uses indentation to indicate a block of code.
 Eg:
 Program
if 5 > 2:
print("Five is greater than two!")
 Output:
Error

Then what is the correct syntax?
 Program
if 5 > 2:
print("Five is greater than two!")
 Output:
Five is greater than two!

Comments
 Python has commenting capability for the purpose of in-code documentation.
 Comments start with a #, and Python will render the rest of the line as a comment:
 Eg:
#This is a comment.
print("Hello, World!")

Docstrings
 Python also has extended documentation capability, called docstrings.
 Docstrings can be one line, or multiline.
 Python uses triple quotes at the beginning and end of the docstring:
 Eg:
”””This is a
multiline docstring.”””
print("Hello, World!")

Exercise:
 Insert the missing part of the code below to output "Hello World".
 _____________(“Hello World”)
 _____This is a comment
 _____ This is a multiline comment”””

Python Variables
 Python has no command for declaring a variable
 A variable is created the moment you first assign a value to it.
 Eg:
 Program
x = 5
y = "John"
print(x)
print(y)
Output
5
John

Python Variables(cont…)
 Variables do not need to be declared with any particular type and can even change
type after they have been set.
 Eg:
Program:
x = 4 # x is of type int
x = "Sally" # x is now of type str
print(x)
Output:
Predict the output

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)

Output variables
 The Python “print” statement is often used to output variables.
 To combine both text and variable, Python uses the “+” character.
 Eg:
Program:
x = "awesome"
print("Python is " + x)
Output:
Python is awesome

Output Variables(cont…)
 You can also use the “+” character to add a variable to another variable.
 Eg:
Program:
x = "Python is "
y = "awesome"
z = x + y
print(z)
Output:
 Predict the output

Output Variables(cont…)
 For numbers, the “+” character works as a mathematical operator
 Eg:
Program:
x = 5
y = 10
print(x + y)
Output:
15

Try this…
 Program:
x = 5
y = "John"
print(x + y)
 Output:
Predict the output

Exercise:
 Create the variable named “carname” and assighn the value “Volvo” to it.
 Create a variable named “x” and assign the value 50 to it.
 Display the sum of “5+10” using two variables :”x” and “y”.
 Create a variable called “z”, assign “x+y” to it , and display the result.

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
 Eg:
x = 1 # int
y = 2.8 # float
z = 1j # complex

Python Numbers(cont…)
 To verify the type of any object in Python, use the type() function.
 Eg:
x = 1 # int
y = 2.8 # float
z = 1j # complex
print(type(x))
print(type(y))
print(type(z))

Python Numbers(cont…)
 Int
 Int, or integer, is a whole number, positive or negative, without decimals, of unlimited
length.
 Float
 Float, or "floating point number" is a number, positive or negative, containing one or
more decimals.
 Float can also be scientific numbers with an "e" to indicate the power of 10.
 Complex
 Complex numbers are written with a "j" as the imaginary part:

Python Casting
 Casting in python is therefore done using constructor functions:
 int() - constructs an integer number from an integer literal, a float literal (by rounding
down to the previous whole number), or a string literal (providing the string represents a
whole number)
 float() - constructs a float number from an integer literal, a float literal or a string literal
(providing the string represents a float or an integer)
 str() - constructs a string from a wide variety of data types, including strings, integer
literals and float literals

Python Casting(cont…)
 Eg: integers
x = int(1)
y = int(2.8)
z = int("3")
print(x)
print(y)
print(z)

Python Casting(cont…)
 Eg: Strings
x = str("s1")
y = str(2)
z = str(3.0)
print(x)
print(y)
print(z)

Strings
 String literals in python are surrounded by either single quotation marks, or
double quotation marks.
 ‘hello’ = “hello”
 Strings can be output to screen using the print function.
 Print(“hello”)
 Strings in Python are arrays of bytes.
 Python does not have a character data type
 a single character is simply a string with a length of 1

Strings(Cont…)
 Square brackets can be used to access elements of the string.
Eg1:
a = "Hello, World!“
print(a[1])
 Substring. Get the characters from position 2 to position 5 (not included):
Eg2:
b = "Hello, World!"
print(b[2:5])

Strings (Cont…)
 The strip() method removes any whitespace from the beginning or the end.
Eg:
a = " Hello, , World! "
print(a.strip()) # returns "Hello, World!"
 The len() method returns the length of a string
Eg:
a = "Hello, World!"
print(len(a))

Strings (cont…)
 The lower() method returns the string in lower case
Eg:
a = "Hello, World!"
print(a.lower())
 The upper() method returns the string in upper case
Eg:
a = "Hello, World!"
print(a.upper())

Strings(Cont…)
 The replace() method replaces a string with another string
Eg:
a = "Hello, World!"
print(a.replace("H", "J"))
 The split() method splits the string into substrings if it finds instances of the
separator
Eg:
a = "Hello, World!"
print(a.split(",")) # returns ['Hello', ' World!']

Exercise
 Method used to find the length of a string.
 Get the first character of the string txt
txt=“hello”
x=?
 Use of strip()?

Python Basics

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