Python language beginners notes

1. Python

2. Introduction
History:
Author : Guido van Rossum
Year:1991
use:
1.Web Development
2.Software Development
3.Mathematics
4.System Scripting
What?
• It is used on a server to create web applications.
• It create workflows
• It connects with database system, to read and modify files.
• It handles Big data and performs Complex mathematical operations.
• It is used for rapid-prototyping.

3. Escape Characters
Code Result
' Single Quote
Backslash
n New Line
r Carriage Return
t Tab
b Backspace
f Form Feed
ooo Octal value
xhh Hex value

4. Special Operators -Escape
• "t" is a tab,
• “n “ New Line

5. Arithmetic Operators
Operator Name Example
+ Addition x + y
- Subtraction x - y
* Multiplication x * y
/ Division x / y
% Modulus x % y
** Exponentiation x ** y
// Floor division x // y

6. Ex
x = 5
y = 3
print(x + y)
print(x - y)
print(x * y)
print(x / y)
print(x % y)
print(x ** y)
print(x //y)

7. Assignment Operators
Operator Example Same As
= x = 5 x = 5
+= x += 3 x = x + 3
-= x -= 3 x = x - 3
*= x *= 3 x = x * 3
/= x /= 3 x = x / 3
%= x %= 3 x = x % 3
//= x //= 3 x = x // 3
**= x **= 3 x = x ** 3
&= x &= 3 x = x & 3
|= x |= 3 x = x | 3
^= x ^= 3 x = x ^ 3
>>= x >>= 3 x = x >> 3
<<= x <<= 3 x = x << 3

8. Comparison Operators
Operator Name Example
== Equal x == y
!= Not equal x != y
> Greater than x > y
< Less than x < y
>= Greater than or equal to x >= y
<= Less than or equal to x <= y

9. Booleans
Boolean Values:
• When you compare two values, the expression is
evaluated and Python returns the Boolean answer:
Example:
print(10 > 9)
print(10 == 10)
print(10 < 9)

10. a = 200
b = 33
if b > a:
print("b is greater than a")
else:
print("b is not greater than a")

11. Evaluate Values and Variables
• The bool() function allows you to evaluate any
value, and give you True or False in return,
• Ex:
print(bool("Hello"))
print(bool(15))
x = "Hello"
y = 15
print(bool(x))
print(bool(y))

12. True:
bool("abc")
bool(123)
bool(["apple", "cherry", "banana"])
False:
bool(False)
bool(None)
bool(0)
bool("")
bool(())
bool([])
bool({})

13. String Coding's
Concatenation
Upper
Lower
Count
Find
Center
Title
Split
IsalNum
Len
Replace
Strip
Rfind
Isdigit
Expandtabs
endswith

14. Python Data Types
Types
• List
• Tuple
• Set
• Dictionary
Declaration
• List Variable Name =[“ “,----]
• Tuple Variable Name = (“ “,-----------)
• Set Variable Name = {“ “, ------------- }
• Dict Variable Name = {Key:Value,------------}

15. List
• Lists are used to store multiple items in a single variable.
Ex:
List Items:
1. Ordered
2. Changeable
3. Allow duplicates

16. List Coding’s
Ratio [::]
Append
Extend
Remove
Pop
Len
Sort
Reverse
Clear
Copy
Join

17. Sets
• Sets are used to store multiple items in a single variable.
• Set Items are:
Unordered
Unindexed
Unchangeable
Duplicates not allowed
• Sets are written with curly [ { } ]brackets.

18. Set Coding’s
Type
Add
Update
Remove
Union
Intersection_update
Symmetric _update [It will keep only the
elements that are NOT present in both sets.]

19. Tuples
• Tuples are used to store multiple items in a single variable.
• Tuple items :
1.Ordered
2.Unchangeable
3.Allow Duplicate values

20. Tuples Coding’s
Type
Len
Min
Max
Join
Change data Type
Multiple [Asterisk* - you can the * Operator the
values will be assigned Multi Times ]

21. Dictionaries
• It is used to store data values in key:value pairs.
• Dictionary Items are:
Ordered
Changeable
Duplicates not allowed
A={"brand": “Window 10,"model": “DellArm", "year": 2020
}
print(A)

22. Dictionary Coding’s
Insert
Update
Pop – [Removes the item with the specified key name]
PopItems – [It removes the last inserted item]
Del
Copy
Clear
Get

23. Functions
• A function is a block of code which only runs
when it is called.
• Parameters which contains the arguments.
• Return the result as data.
Ex:
def my_function():
print("Hello from a function")

24. Function Call
def my_function():
print("Hello from a function")
my_function()
Arguments:
def my_function(fname):
print(fname + " Refsnes")
my_function("Emil")
my_function("Tobias")
my_function("Linus")

25. Return
def my_function(x):
return 5 * x
print(my_function(3))
print(my_function(5))
print(my_function(9))

26. Pass
• function definitions cannot be empty.
• But due to some reason have a function
definition without content, use pass
statement to avoid an error.
Ex:
def myfunction():
pass

27. Class and object
• It is an Object Oriented Programming.
• Class:
Collection of objects.
Blueprint for creating objects.
• Object:
Basic Run time entity.

28. Class creation:
class MyClass:
x = 5
print(MyClass)
Object Creation:
c1=Myclass
Ex:
class MyClass:
x = 5
c1 = MyClass()
print(c1.x)

29. __init__()
• All classes have a function called __init__()
• It is executed when the class is being initiated.
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
p1 = Person("John", 36)
print(p1.name)
print(p1.age)

30. Object methods
• Objects can also contain methods.
• Methods in objects are functions that belong to the object.
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
def myfunc(self):
print("Hello my name is " + self.name)
p1 = Person("John", 36)
p1.myfunc()

31. Inheritance
• a class that inherits all the methods and properties
from another class.
• Parent class is the class being inherited from, also
called base class.
• Child class is the class that inherits from another
class, also called derived class.

32. Parent Class:
class Person:
def __init__(self, fname, lname):
self.firstname = fname
self.lastname = lname
def printname(self):
print(self.firstname, self.lastname)
x = Person("John", "Doe")
x.printname()
Child Class:
class Student(Person):
pass

33. class Person:
def __init__(self, fname, lname):
self.firstname = fname
self.lastname = lname
def printname(self):
print(self.firstname, self.lastname)
class Student(Person):
pass
x = Student("Mike", "Olsen")
x.printname()

34. __init__() Function
• add the __init__() function to the child class (instead of
the pass keyword).
Ex:
class Student(Person):
def __init__(self, fname, lname):
class Student(Person):
def __init__(self, fname, lname):
Person.__init__(self, fname, lname)

35. super() Function
• super() function that will make the child class inherit all the
methods and properties from its parent:
class Student(Person):
def __init__(self, fname, lname):
super().__init__(fname, lname)

36. Iterators
• An iterator is an object that contains a countable number of values.
• Methods to iterate:
__iter__()
__next__()
Iterator vs Iterable
Lists, tuples, dictionaries, and sets are all iterable objects.
Ex:
mytuple = ("apple", "banana", "cherry")
myit = iter(mytuple)
print(next(myit))
print(next(myit))
print(next(myit))

37. Looping Through an Iterator
• for loop to iterate through an iterable object:
mytuple = ("apple", "banana", "cherry")
for x in mytuple:
print(x)
mystr = "banana"
for x in mystr:
print(x)

38. Create an Iterator
• __iter__() and __next__() methods used to create an
object/class as an iterator.
• __init__() used to do some initialization when an object being
created.
• __iter__() - you can do operations (initializing etc.), but must
always return the iterator object itself.
• __next__() - method also allows you to do operations, and
must return the next item in the sequence.

39. StopIteration
• To prevent the iteration to go on forever, we can use
the StopIteration statement.
• __next__() – Add an termination condition to raise an error, if
the iteration is done a specified number of times.

40. class MyNumbers:
def __iter__(self):
self.a = 1
return self
def __next__(self):
if self.a <= 20:
x = self.a
self.a += 1
return x
else:
raise StopIteration
myclass = MyNumbers()
myiter = iter(myclass)
for x in myiter:
print(x)

41. Scope of Variables
• A variable is only available from inside the
region it is created. This is called scope.
• Two types:
Local
Global

42. Local:
A variable created inside a function, and can be used
inside the function.
Ex:
def myfunc():
x = 300
print(x)
myfunc()

43. Function Inside Function [Inner Func]
def myfunc():
x = 300
def myinnerfunc():
print(x)
myinnerfunc()
myfunc()

44. Global Scope:
A variable created in the main body of the Python code is
a global variable.
Ex:
x = 300
def myfunc():
print(x)
myfunc()
print(x)

45. Naming Variables:
When we use the same variable name inside and outside
of a function, Python will treat them as two separate variables.
x = 300
def myfunc():
x = 200
print(x)
myfunc()
print(x)

46. Global Keyword:
It represents a Global Scope.
The keyword used to change the value of a global
variable.
def myfunc():
global x
x = 300
myfunc()
print(x)

47. File Handling
• File handling is an important part of any web
application.
• Functions:
Creating
Reading
Updating
Deleting

48. File Open
• Function : open()
• Parameters: filename, and mode.
• Modes:
“r” – Read
“a” – Append
“w” – Write
“x” – Create
• Syntax:
f = open(“SS.txt")
f = open(“SS.txt", "rt")

49. Read Files:
• Function: read()
• f = open("demofile.txt", "r")
print(f.read())
• f = open("D:myfileswelcome.txt", "r")
print(f.read())
Reading a part of file:
• f = open("demofile.txt", "r")
print(f.read(5))
Read Lines
• f = open("demofile.txt", "r")
print(f.readline())

50. readline()
• f = open("demofile.txt", "r")
print(f.readline())
print(f.readline())
Loop:
• f = open("demofile.txt", "r")
for x in f:
print(x)

51. Close Files:
• f = open("demofile.txt", "r")
print(f.readline())
f.close()

52. Write to an Existing File
• "a" - Append
• "w" - Write
• f = open("demofile2.txt", "a")
f.write("Now the file has more content!")
f.close()
f = open("demofile2.txt", "r")
print(f.read())
• f = open("demofile3.txt", "w")
f.write("Woops! I have deleted the content!")
f.close()
f = open("demofile3.txt", "r")
print(f.read())

53. Create a New File
• "x" - Create - will create a file, returns an error if
the file exist
• f = open("myfile.txt", "x")
• "a" - Append - will create a file if the specified file
does not exist
• "w" - Write - will create a file if the specified file
does not exist
• f = open("myfile.txt", "w")

54. Delete File
• To delete a file, you must import the OS module.
• Function: os.remove()
• import os
os.remove("demofile.txt")
Check if File exist:
import os
if os.path.exists("demofile.txt"):
os.remove("demofile.txt")
else:
print("The file does not exist")

55. Delete Folder
• To delete an entire folder, use
the os.rmdir() method:
• import os
os.rmdir("myfolder")