Programming in Python (IT-605) - Important Questions

Explain the rules for naming Python identifiers. Give at least five examples of valid identifiers and five examples of invalid identifiers with brief explanations for each.

Write a Python program that reads a string from input and determines whether it is a valid Python identifier. Use appropriate standard library features (for example, $str.isidentifier()$) and display clear messages for valid and invalid cases.

Differentiate between Python identifiers and Python keywords. Show how to list all Python keywords programmatically and provide examples where a keyword cannot be used as an identifier.

Explain the significance of leading and trailing underscores in Python identifiers: single leading underscore (e.g. $_var$), single trailing underscore (e.g. $var\_$), double leading underscores (e.g. $__var$) and double leading and trailing underscores (e.g. $__init__$). Illustrate with examples showing name mangling and the use of special ("dunder") methods.

Describe PEP 8 naming conventions for Python identifiers. Explain recommended styles for variables, functions, classes, constants, and modules and why following these conventions is important.

Are Python identifiers case-sensitive? Explain with concise examples that demonstrate different identifiers differing only in case and their behavior.

Discuss whether Python identifiers may contain Unicode characters. Explain the rules, give examples of Unicode identifiers, and describe potential issues when using non-ASCII identifiers in source code.

Trace the output of the following code and explain each line of output with reference to identifier resolution and name mangling:

class A: def init(self): self.__x = 10

def get_x(self):
    return self.__x

obj = A() print(obj.get_x()) print(hasattr(obj, '_A__x')) print(getattr(obj, '_A__x'))