Python building block Part 1

1.2 Python building block 

Python, like any programming language, has fundamental elements that form the foundation of its programs. These building blocks include basic syntax, data types, control structures, and functions, among others. Understanding these is key to writing efficient and effective Python code.

1. Indentation :-

Why Is Indentation Important?

• Defines Code Blocks: Indentation indicates a block of code, such as within loops, functions, or conditionals.
• Improves Readability: Indented code is easier to read and understand.
• Mandatory: Python will throw an error if the indentation is incorrect.

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Rules of Indentation in Python

1.    Consistent Indentation: Use the same number of spaces or tabs throughout a block of code.

2.    Preferred Style: Use 4 spaces for each level of indentation (as recommended by PEP 8, Python's style guide).

3.    No Mixing: Do not mix tabs and spaces in the same file, as this can cause errors.

2. Identifiers in Python

Identifiers in Python are the names used to identify variables, functions, classes, modules, and other objects. They are user-defined names that must follow specific rules and conventions.

Rules for Naming Identifiers

1.    Allowed Characters:

o   Can contain letters (a-z, A-Z), digits (0-9), and underscores (_).

o   Must not start with a digit.

valid_name = 10  # Valid

2nd_name = 20    # Invalid

2.    Case Sensitivity:

o   Identifiers are case-sensitive, meaning Name and name are different.

Name = "Alice"

name = "Bob"

print(Name)  # Outputs: Alice

print(name)  # Outputs: Bob

3.    No Reserved Words:

o   Keywords (reserved words) cannot be used as identifiers.

def = 5  # Invalid: 'def' is a reserved word in Python

4.    Special Characters:

o   Cannot contain special characters like @, $, %, etc.

my$name = 50  # Invalid

5.    No Spaces:

o   Spaces are not allowed in identifiers. Use underscores _ instead.

first_name = "Alice"  # Valid

first name = "Bob"    # Invalid

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Examples of Valid and Invalid Identifiers

Valid Identifiers	Invalid Identifiers
my_var	my-var
value1	1value
_temp	temp!
user_name	user name

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Conventions for Naming Identifiers

Although Python does not enforce these, following conventions improves code readability and maintainability:

1.    Variable Names:

o   Use lowercase letters, and separate words with underscores (snake_case).

max_value = 100

user_name = "Alice"

2.    Function Names:

o   Use lowercase letters with underscores between words.

def calculate_area(radius):

    return 3.14 * `radius * radius

3.    Class Names:

o   Use PascalCase (capitalize the first letter of each word).

class Circle:

    pass

4.    Constant Names:

o   Use all uppercase letters with underscores.

PI = 3.14159

MAX_LIMIT = 100

5.    Private Identifiers:

o   Prefix with a single underscore (_) to indicate a non-public identifier.

_internal_data = 42

6.    Special Identifiers:

o   Prefix and suffix with double underscores (__) for special methods.

def __init__(self):

    pass

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Built-in Functions and Identifiers

Python provides many built-in functions like print(), len(), etc. Avoid using their names for your identifiers, as it can overwrite these functions.

Example:

print = 5  # Avoid doing this

print("Hello")  # This will raise an error

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Good Practices

·        Choose meaningful names:

# Bad

x = 50

# Good

max_speed = 50

·        Follow conventions for consistent and readable code.

·        Avoid overly long names.

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Example: Identifiers in a Program

# Valid identifiers

user_name = "Alice"

age = 25

# Function with a proper identifier

def calculate_age_in_days(age):

    return age * 365

# Calling the function

print(f"{user_name} is {calculate_age_in_days(age)} days old.")

Variable

• Variables: Used to store data.

x = 10  # Integer

y = 3.14  # Float

name = "Python"  # String

is_active = True  # Boolean

• Data Types:
• Numeric: int, float, complex
• Sequence: str, list, tuple
• Set: set, frozenset
• Mapping: dict
• Boolean: True, False
• NoneType: None

2. Operators

• Arithmetic Operators: +, -, *, /, %, //, **

Used to perform basic mathematical operations.

Operator	Description	Example
+	Addition	5 + 3 = 8
-	Subtraction	5 - 3 = 2
*	Multiplication	5 * 3 = 15
/	Division	5 / 2 = 2.5
%	Modulus (remainder)	5 % 2 = 1
**	Exponentiation (power)	5 ** 3 = 125
//	Floor division(integer value)	5 // 2 = 2

• Comparison Operators: ==, !=, >, <, >=, <=
  Relational (Comparison Operator): Used to compare two values and return a Boolean result (True or False).

Operator	Description	Example
==	Equal to	5 == 3 → False
!=	Not equal to	5 != 3 → True
>	Greater than	5 > 3 → True
<	Less than	5 < 3 → False
>=	Greater than or equal to	5 >= 3 → True
<=	Less than or equal to	5 <= 3 → False

• Logical Operators: and, or, not
  Logical Operator are used to combine conditional statements.

Operator	Description	Example
and	Returns True if both conditions are True	(5 > 3 and 2 > 1) → True
or	Returns True if at least one condition is True	(5 > 3 or 2 < 1) → True
not	Reverses the result	not(5 > 3) → False

• Bitwise Operator: Operate at the binary level.
  

Operator	Description	Example
&	AND	5 & 3 → 1
`	`	OR
^	XOR	5 ^ 3 → 6
~	Complement	~5 → -6
<<	Left shift	5 << 1 → 10
>>	Right shift	5 >> 1 → 2

• Assignment Operators: =, +=, -=, *=, /=, etc.

Assignment Operator used to assign values to variables.

Operator	Description	Example
=	Assign	x = 5
+=	Add and assign	x += 3 → x = x + 3
-=	Subtract and assign	x -= 3 → x = x - 3
*=	Multiply and assign	x *= 3 → x = x * 3
/=	Divide and assign	x /= 3 → x = x / 3
%=	Modulus and assign	x %= 3 → x = x % 3
**=	Exponentiate and assign	x **= 3 → x = x ** 3
//=	Floor divide and assign	x //= 3 → x = x // 3

• Membership Operators: in, not in,range

Membership Operator: Used to test if a value is in a sequence (like a list, string, or tuple).

Operator	Description	Example
in	Returns True if the value is present in the sequence	"a" in "apple" → True
not in	Returns True if the value is not present in the sequence	"b" not in "apple" → True

• Identity Operators: is, is not

Identity Operator used to compare the memory locations of two objects.

Operator	Description	Example
is	Returns True if both variables point to the same object	x is y → True
is not	Returns True if both variables point to different objects	x is not y → True

# Arithmetic Operators

a, b = 5, 3

print("Addition:", a + b)        # 8

print("Exponentiation:", a ** b)  # 125

# Comparison Operators

print("Is a greater than b?", a > b)  # True

# Logical Operators

print("Logical AND:", a > 2 and b < 5)  # True

# Membership Operators

lst = [1, 2, 3, 4, 5]

print("Is 3 in the list?", 3 in lst)   # True

# Identity Operators

x = [1, 2, 3]

y = [1, 2, 3]

print("x is y:", x is y)  # False (different objects in memory)