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Identifiers in Python

Identifiers are the names used to identify variables, functions, classes, modules, or other objects in Python. They are user-defined names and play a significant role in making the code readable and meaningful.

1. Characteristics of Identifiers:

  1. Unique Names: They should uniquely represent variables, functions, or objects.
  2. Case-Sensitive: Python distinguishes between uppercase and lowercase letters. For example, name and Name are different identifiers.
  3. Must Start with a Letter or Underscore (_): The first character must be an alphabet (A-Z or a-z) or an underscore.
  4. Cannot Use Special Characters: Identifiers cannot contain symbols like @, #, $, %, etc.
  5. Can Include Letters, Digits, and Underscores: After the first letter, digits (0-9) can be used.
  6. Cannot Be a Keyword: Identifiers cannot be the same as Python’s reserved keywords.

2. Rules for Naming Identifiers:

a. Allowed Identifiers:

  • Must follow the naming conventions.
  • Examples:

age = 25

first_name = “John”

_temp = 100

b. Invalid Identifiers:

  • Start with a digit:

1name = “Invalid”  # SyntaxError

  • Contain special characters:

name@ = “Invalid”  # SyntaxError

  • Match Python keywords:

def = 10  # SyntaxError

3. Naming Conventions:

Adhering to conventions improves code readability and maintainability.

  1. Variables and Functions:
    1. Use lowercase letters.
    1. Separate words with underscores (snake_case).

student_name = “Alice”

calculate_sum = lambda x, y: x + y

  • Constants:
    • Use uppercase letters, separated by underscores.

PI = 3.14159

MAX_VALUE = 100

  • Classes:
    • Use CamelCase.

class Person:

    pass

  • Private Identifiers:
    • Use a single underscore prefix for non-public identifiers.

_private_var = 10

  • Special Identifiers:
    • Use double underscores for special methods or system-defined names (dunder methods).

def __init__(self):

    pass

4. Examples of Identifiers:

Valid Identifiers:

name = “Alice”

_age = 25

total_1 = 100

sum_of_values = 50

Invalid Identifiers:

1name = “Bob”       # SyntaxError: cannot start with a digit

total# = 10         # SyntaxError: special character not allowed

for = 15            # SyntaxError: ‘for’ is a keyword

5. Reserved Identifiers:

While identifiers are user-defined, some names are system-defined or reserved for specific functionalities (e.g., __name__, __main__). Avoid using them unless necessary.

6. Best Practices for Identifiers:

  • Use meaningful names to describe the purpose of the variable or function.

# Bad

x = 10

# Good

student_age = 10

  • Avoid overly long names; keep them concise yet descriptive.
  • Stick to one naming convention throughout the project for consistency.
  • Avoid single-character names unless in loops (i, j, k).

Conclusion:

Identifiers are the building blocks of Python programming, giving structure and clarity to the code. By adhering to naming conventions and rules, developers can write more readable, maintainable, and error-free programs.