Python identifiers follow some basic rules: 1. They can include letters, numbers, and underscores. 2. They cannot start with a number. 3. Keywords like "if" cannot be used. 4. Identifiers are case-sensitive. Of the given options, valid Python identifiers include: total1234, _abc_abc_, _p. Invalid ones include: 123total (can't start with number), java2share (contains special character), ca$h (contains special character), def (is a keyword).

1. Identifiers :
An identifier is a name given to a variable,function,class.
Eg: a = 20
It is a valid Python statement.
Here 'a' is an identifier.
Rules to define identifiers in Python:
1. The only allowed characters in Python are
Alphabet symbols(either lower case or upper case)
Digits(0 to 9)
Underscore symbol(_).
Ex: total_1234 = 22 # Valid

2. 2. An Identifier can be begin with an alphabet and underscoret(A-Z and a-z
and_)
Ex: _abc_abc_ = 22 # Valid
3. Identifier cannot starts with digit but is allowed everywhere else.
Ex: plus1=10 #valid
1plus=10 # In valid
SyntaxError: invalid syntax
3.One cannot use spaces and special symbols like ! @ # $ % etc….
as identifiers.
Ex: cash$ = 10 # '$'is a special character invalid identifier
SyntaxError: invalid syntax
4. Identifiers are case sensitive. Of course Python language itself is case
sensitive language.
Ex: total=10
TOTAL=999
print(total) o/p : 10
print(TOTAL) o/p : 999

3. 4.Keywords cannot be used as identifiers.
Ex: x = 10 # Valid
if = 33 # In valid if is a keyword in Python
SyntaxError: invalid syntax
5. Identifiers can be of any length.
Ex : Abcedwrtyyhfdg123_=10
Q. Which of the following are valid Python identifiers?
123total = 22
total1234 = 22
java2share = 'Java‘
ca$h = 33
_abc_abc_ = 22
def = 44
for = 3
_p = 33

4. Keywords:
1. In Python some words are reserved to represent some
meaning or functionality. Such type of words are called
Reserved words or keywords.
2. There are 33 reserved words available in Python.
List of keywords in python:
and as not
assert finally or
break for pass
class from nonlocal
continue global raise
def if return
del import try
elif in while
else is with
except lambda yield
False True None

5. 2. All 33 keywords contains only alphabets symbols.
3. Except the following 3 reserved words, all contain only
lowercase alphabet symbols.
True
False
None
4. True and False are Boolean values , For Boolean values,
compulsory you need to use capital letter 'T' in True and
capital letter 'F' in False.
Ex: a = True # Valid
A=true # In valid
NameError: name 'true' is not defined

6. Statements and Expressions:
A statement is an instruction or statement is a unit of code that can be executed by
python interpreter.
Eg: z = 1 // this iExamples: Y=x + 17 >>> x=10 >>> z=x+20 >>> z 30 s an assignment
statement
Expression:
An expression is a combination of values, variables, and operators which are evaluated
to make a new value b.
>>> 20 # A single value
>>> z # A single variable
>>> z=10 # A statement
But expression is a combination of variable, operator and value which is evaluated by
using assignment operator in script mode.
Examples: Y=x + 17
>>> x=10 >>> z=x+20 >>> z o/p : 30
When the expression is used in interactive mode, is evaluated by the interpreter and
the result is displayed instantly.
Eg:
>>> 8+2
10

7. Variables:
Variables are nothing but reserved memory locations to store
values. That means when you create a variable some space is
reserved in memory.
• One of the most powerful features of a programming language
is the ability to manipulate variables.
• A variable is a name that refers to a value. An assignment
statement creates new variables and gives them values:
• The general format for assigning values is as follows.
• Variable name = expression
• The equal sign (=) also known as simple assignment operator
is used to assign values to variables.
• In general format, the operand to the left of the = operator is
the name of the variable and operator to the right of the =
operator is the expression which can be a value.

8. Eg:1. >>>name=‘python’
>>> number=100
>>> miles=1000.0
>>> name
Python
>>> number
100
>>> miles
1000
• This example makes three assignment statements.
• Integer type assigned to a variable number, float type assigned
to a variable miles ,string type value is assigned to a variable
name and print the value assigned to these variables.

9. 2. In python not only the value of variable may change during program
execution but also the type of data that is assigned.
In Python, We don't need to specify the type of variable because
Python is a loosely typed language.
>>>Century=100
>>> Century = “hundred”
>>> Century
‘hundred’
3. Python allows you to assign value to several variables
simultaneously.
1. >>> a=b=c=1 4.Assign multiple values to multiple variables
2.>>> a
1 a,b,c=5,50, 15
3.>>> b >>> a 5
1 >>>b 50
4.>>> c >>>c 15
1

10. Operators in Python
• The operator can be defined as a symbol which is responsible
for a particular operation between two operands.
• Python provides a variety of operators described as follows.
• Arithmetic operators :
• + (addition) eg: a=20; b=10 then a + b=30
• - (subtraction) eg: a=20; b=10 then a - b=10
• *(multiplication) eg: a=20; b=10 then a * b=200
• / (divide) eg: a=20; b=10 then a / b=2
• %( reminder) eg: a=20; b=10 then a % b=0
• // (floor division) eg: a=24; b=7 then a // b=3
• ** (exponent) eg: a=2; b=3 then a ** b=8

12. Operators in Python
• Assignment operators :
• = (Assigns to)
• += (Assignment after Addition)
• -= (Assignment after Subtraction)
• *= (Assignment after Multiplication)
• /= (Assignment after Division)
• %= (Assignment after Modulus)
• **= (Assignment after Exponent)
• //= (Assignment after floor division)

14. • Comparison operators :
• == (Equal to)
• != (Not equal to)
• <= (Less than or equal)
• >= (Greater than or equal)
• < (Less than)
• > (Greater than)

15. • Logical operators :
• and (logical and)
• or (logical or)
• not (logical not)

16. • Bitwise operators :
• & (binary and)
• | (binary or)
• ^ (binary xor)
• ~ (negation)
• << (left shift)
• >> (right shift)
• Membership operators :
• in (True, If the value is present in the data structure)
• not in (True, If the value is not present in the data structure)
• Identity operators :
• is (Returns true if both variables are the same object)
• is not (Returns true if both variables are not the same object)

18. Precedence and Associativity

19. Comments in Python
• In general, Comments are used in a programming language
to describe the program or to hide the some part of code
from the interpreter.
• Comments in Python can be used to explain any program
code. It can also be used to hide the code as well.
• Comment is not a part of the program, but it enhances the
interactivity of the program and makes the program
readable.
Python supports two types of comments:
• Single Line Comment
• Multi Line Comment

20. Comments in Python
• Single Line Comment:
In case user wants to specify a single line comment, then comment must start
with ‘#’
Example:
# This is single line comment
print "Hello Python"
Output:
Hello Python
• Multi Line Comment:
Multi lined comment can be given inside triple quotes.
Example:
'''This is
Multiline
Comment'''
print "Hello Python"
Output:
Hello Python

21. • Data types:
• Data types specify the type of data like numbers and characters to be stored
and manipulated with in a program. Basic data type of python are
• Numbers
• Boolean
• Strings
• None
Numbers:
• Integers, floating point numbers and complex numbers fall under python
numbers category. They are defined as int, float and complex class in
python.
1. integer:
• Int, or integer, is a whole number, positive or negative, without decimals,
of unlimited length, it is only limited by the memory available.
Example:
a=10
b=-12
c=123456789

22. 2. float:
• Float or "floating point number" is a number, positive or negative, containing
one or more decimals.
Example:
• X=1.0
• Y=12.3
• Z= -13.4
3. complex:
• Complex numbers are written in the form , “x+yj" where x is the real part and
y is the imaginary part.
Example:
A=2+5j
B=-3+4j
C=-6j
Boolean:
Booleans are essential when you start using conditional statements.
Python Boolean type is one of the built-in data types provided by Python,
which represents one of the two values i.e. True or False. The boolean
values, True and False treated as reserved words.

23. String:
• The string can be defined as the sequence of characters
represented in the quotation marks. In python, we can use single,
double, or triple quotes to define a string.
• In the case of string handling, the operator + is used to concatenate
two strings as the operation "hello"+" python" returns "hello
python".
Example:
EX : S1=‘Welcome’ #using single quotes
S1 Output: ‘Welcome’
print(S1) Output: Welcome
Ex: S2=“To” #using double quotes
S2 Output: 'to'
print(S2) Output: to
Ex: S3=‘’’Python’’’ #using triple quotes
S3 Output: "'python'"
print(S3) Output: 'python‘
Ex: Name1= ‘Hello’
Name2=‘python’
Name1 + Name2 Output: ‘Hellopython’
print(Name1 + Name2) Output: Hellopython

24. Example:
a=10
b=“Python"
c = 10.5
d=2.14j
e=True
print("Data type of Variable a :",type(a))
print("Data type of Variable b :",type(b))
print("Data type of Variable c :",type(c))
print("Data type of Variable d :",type(d))
print(“Data type of Variable e :”,type(e))
Output:
• Data type of Variable a : <class 'int'>
• Data type of Variable b : <class 'str'>
• Data type of Variable c : <class 'float'>
• Data type of Variable d : <class 'complex'>
• Data type of Variable e : <class 'bool'>

25. Indentation:
• In Python it is a requirement and not a matter of style to indent the
program. This makes the code cleaner and easier to understand and
read.
• If a code block has to be deeply nested, then the nested statements
need to be indented further to the right.
• Block 2 and Block 3 are nested under Block 1. 4 white spaces are
used for indentation and are preferred over tabs.
• Incorrect indentation will result in IndentationError.
Block 1
Block 2
Block 3
Block 2, Continuation
Block 1, Continuation

26. • Reading Input :
• Input() function is used to gather data from the user.
• Syntax : variable_name = input([prompt])
• Where prompt is a string written inside parenthesis.
• The prompt gives an indication to the user of the value that needs
to be entered through the keyboard.
• When user presses Enter key, the program resumes and input
function returns what the user typed as a string.
• Even if the user inputs a number, it is treated as a string and the
variable_name is assigned the value of string.
1. >>> person = input(“what is your name?”)
2. What is your name? John
3. >>>person
4. ‘John’

27. Print Output
• Print() function allows a program to display text onto the console.
• Print function prints everything as strings.
>>>print(“Hello World”)
Hello World
There are two major string formats which are used inside the print() function to display
the contents on to the console.
1. str.format()
2. f-strings
str.format() method:
• The format() method returns a new string with inserted values.
• syntax: str.format(p0,p1,p2…..k0=v0, k1=v1,…)
• Where p0,p1 are called as positional arguments and k0,k1 are keyword arguments
with their assigned values of v0,v1..
• Positional arguments are a list of arguments that can be accessed with an index of
argument inside curly braces like {index}. Index value starts from zero.
• Keyword arguments are a list of arguments of type keyword = value, that can be
accessed with the name of the argument inside curly braces like {keyword}.
Eg: country = input(“which country do you live in”)
print(“I live in {0}”.format(country))

28. • Print Output
Eg:
a = 10
b = 20
Print(“the values of a is {0} and b is {1}”.format(a,b))
Print(“the values of b is {1} and a is {0}”.format(a,b))
f-strings:
A f-string is a string literal that is prefixed with “f”. These strings
may contain replacement fields ,and are enclosed within
curly braces { }.
Eg: country = input(“which country do you live in”)
Print(f”I live in {country}”)

29. Type Conversion in Python:
• Python provides Explicit type conversion functions to directly convert
one data type to another. It is also called as Type Casting in Python
• Python supports following functions
1. int () : This function convert a float number or a string to an integer.
• Eg: float_to_int = int(3.5)
string_to_int = int(“1”) // number is treated as string
print(float_to_int) o/p: 3
print(string_to_int) o/p: 1 will be displayed.
2. float( ) :
• This function convert integer or a string to floating point number using the
float() function.
• Eg: int_to_float = float(8)
string_to_float = float(“1”) // number is treated as string
print(int_to_float)
print(string_to_float)
8.0
1.0 get displayed

30. • The str() Function : The str() function returns a string which is fairly human
readable.
Eg: int_to_string =str(8)
float_to_string = str(3.5)
Print(int_to_string) prints ‘8’
Print(float_to_string) prints ‘3.5’
• The chr() Function : This function converts an integer to a string of one
character whose ASCII is the same integer used in chr() function. The
integer value should be in the range of 0-255.
Eg: ascii_to_char = chr(100)
Print(“equivalent character for ASCII value of 100 is {ascii_to_char}”)
Output: equivalent character for ASCII value of 100 is d
An integer value corresponding to an ASCII code is converted to character
and printed.
(ASCII A-Z =65 to 90 ; a-z = 97 to 122; 0-9 = 48 to 57)

31. • The Complex() Function:
• complex() function is used to print a complex number with a real part and
imag*j part.
• If the first argument for the function is a string, it is interpreted as complex
number and the function is called without 2nd parameter.
• If imag is omitted, it defaults to zero
• Eg: complex_with_string = complex(“1”)
– complex_with_number = complex(5,8)
Print(f“result after using string in real part{complex_with_string}”)
– Print(f”result after using numbers in real and imaginary
part{complex_with_number}”)
– Output: result after using string in real part (1+0j)
– result after using numbers in real and imaginary part (5+8j)

32. The ord() function:
• The ord() function returns an integer representing Unicode
code point for the given Unicode character.
• Eg: 1. unicode_for_integer = ord('4')
print(f“ Unicode code point for integer value of 4 is
{unicode_for_integer}")
Output: Unicode code point for integer value of 4 is 52.
The hex() function:
• Convert an integer number (of any size) to a lowercase
hexadecimal string prefixed with “0x” using hex() function.
• 1. int_to_hex = hex(255)
• 2. print(int_to_hex )
• Output: 0xff

33. The oct() function:
• Convert an integer number (of any size) to an octal string prefixed with “0o” using
oct() function.
Eg: int_to_oct = oct(255)
print(int_to_oct)
Output: 0o377.
Dynamic and strongly typed language:
• Python is a dynamic language as the type of the variable is determined during run-
time by the interpreter.
• Python is also a strongly typed language as the interpreter keeps track of all the
variables types
• In a strongly typed language, you are simply not allowed to do anything that’s
incompatible with the type of data you are working with.
• For example, Parts of Python Programming Language
>>> 5 + 10
15
>>> 1 + "a“
Traceback (most recent call last):
• when you try to add 1, which is an integer type with "a" which is string type, then
it results in Traceback as they are not compatible.
• In Python, Traceback is printed when an error occurs.

34. The type() function and is operator:
The syntax for type() function is,
type(object)
The type() function returns the data type of the given object.
1. >>> type(1)
<class ‘int’>
2. >>> type(6.4)
<class ‘float’>
3. >>> type("A")
<class ‘str’>
4. >>> type(True)
<class ‘bool’>
The type() function comes in handy if you forget the type of
variable or an object during the course of writing programs.