2. 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.
3. 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.
4. 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.
7. 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
8. Then what is the correct syntax?
Program
if 5 > 2:
print("Five is greater than two!")
Output:
Five is greater than two!
9. 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!")
10. 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!")
11. Exercise:
Insert the missing part of the code below to output "Hello World".
_____________(“Hello World”)
_____This is a comment
_____ This is a multiline comment”””
12. 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
13. 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
14. 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)
15. 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
16. 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
17. Output Variables(cont…)
For numbers, the “+” character works as a mathematical operator
Eg:
Program:
x = 5
y = 10
print(x + y)
Output:
15
19. 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.
20. 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
21. 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))
22. 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:
23. 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
26. 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
27. 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])
28. 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))
29. 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())
30. 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!']
31. Exercise
Method used to find the length of a string.
Get the first character of the string txt
txt=“hello”
x=?
Use of strip()?
