Python MCQ Questions

Abstract base class (ABC): defines interface without implementation. Use abc module. Example: from abc import ABC, abstractmethod; class Base(ABC): @abstractmethod def method(self): pass. Subclasses must implement abstract methods. Cannot instantiate abstract class. Interface definition pattern.

Returns '1'. ('123')[0] indexes string '123' at position 0. Parentheses don't make tuple without comma. Just grouped expression. String indexing: first character is '1'. Not tuple access. Result: character '1' as string. Difference from ('123',)[0] which returns whole string '123'.

Use itertools.chain() to combine iterables. Example: chain([1, 2], [3, 4]) yields 1, 2, 3, 4. chain.from_iterable() for nested. Flattens sequences. Sequential combination.

Metaclass is class of a class. Defines class behavior. type is default metaclass. Custom metaclasses inherit from type. Control class creation. Override __new__, __init__. Example: class Meta(type): pass. Applied: class MyClass(metaclass=Meta): pass. Advanced feature for framework development. Metaclasses define how classes behave.

Use logging.basicConfig() to configure logging. Example: logging.basicConfig(level=logging.INFO). Levels: DEBUG, INFO, WARNING, ERROR, CRITICAL. logging.info('message') logs. Better than print() for production.

Use asyncio for asynchronous I/O: async def coroutine(): await async_operation(). Event loop manages execution. Non-blocking I/O. Example: asyncio.run(main()). async/await syntax (Python 3.5+). Cooperative multitasking. Single-threaded concurrency. Scalable I/O operations.

Fundamental difference: lists are mutable (changeable), tuples are immutable (unchangeable). Lists use [brackets], tuples use (parentheses). After creation, tuple elements cannot be added/removed/modified. Lists can be modified. Tuples faster, hashable (can be dict keys), safer for constant data. Lists for dynamic collections.

Use itertools.repeat(value, times) for repetition. Example: repeat('A', 3) yields 'A' three times. No times: infinite. Constant value generation. Repetition utility.

Strings delimited by single quotes 'text', double quotes "text", or triple quotes '''text''' or """text""". Single and double functionally identical. Triple quotes allow multi-line strings and docstrings. Escape quotes inside: 'it\'s' or "it's". Choose delimiter based on string content to avoid escaping.

Use re.split(pattern, string) to split by pattern. Example: re.split(r'\s+', 'a b c') gives ['a', 'b', 'c']. More flexible than str.split(). maxsplit limits splits. Pattern-based splitting.

Output: (-1+0j). 1j * 1J equals 1j * 1j. j and J both represent imaginary unit. Imaginary unit squared: j*j = -1. Result: -1 (complex number with real part -1, imaginary part 0). Complex number arithmetic. i² = -1 principle.

Use __call__(self, ...) to make object callable. Example: def __call__(self, x): return self.func(x). Enables obj(args) syntax. Objects as functions. Callable classes. Functor pattern. Check with: callable(obj).

Set comprehension: {expression for item in iterable}. Example: {x**2 for x in range(5)} creates {0, 1, 4, 9, 16}. Curly braces like sets. Automatically removes duplicates. Optional condition. Concise set creation from iterable. Set builder notation.

Use functools.reduce(function, iterable) for accumulation. Example: reduce(lambda x, y: x+y, [1, 2, 3, 4]) sums to 10. Binary function accumulates. Optional initializer. Folding operation.

string.lower('RR') is incorrect syntax. Correct: 'RR'.lower() returns 'rr'. Lower() is string method, not function. Call on string object: str_var.lower(). Module string exists but method syntax is str.lower(). Result of correct syntax: 'rr' (lowercase).

Use math.pow(x, y) for exponentiation. Example: math.pow(2, 3) = 8.0. Always returns float. Use ** operator or built-in pow() for integers. Power function.

Pickle is Python serialization format for converting objects to byte streams. pickle module serializes/deserializes Python objects. pickle.dump() saves objects, pickle.load() restores. Preserves object structure, types. Not secure with untrusted data. Used for saving: complex data, ML models, cache. Python-specific format.

Output: (Python 2) or (Python 3). type(lambda:None) returns function type. Lambda creates function object. type() returns object's type. Lambda is first-class object of function type. Demonstrates functions as objects.

Default recursion limit: 1000 (typically). Prevents infinite recursion stack overflow. sys.getrecursionlimit() returns current limit. Platform-dependent but usually 1000. Exceeding limit raises RecursionError. Limit protects against stack exhaustion. Most algorithms shouldn't require changing default.

Python 3: 3/2 = 1.5 (true division, float result). Python 2: 3/2 = 1 (integer division). Python 3 changed division behavior. All / operations return float. Use // for integer division: 3//2=1. Version determines result. Python 3 consistent floating-point division.

Python 3 equivalent: print('Smarterer', 'Tests', file=f, end=''). file parameter redirects output. end='' prevents newline (Python 2 trailing comma). print() function with file and end parameters. Python 3 print() is function requiring parameters.

Type of [' '] is list. Square brackets always denote list, even with one element. Contains single string element ' ' (space). Not string, not tuple. List with one element. Access: lst[0]. Lists can contain any type including empty strings or whitespace.

match() checks pattern at string start only, anchored to beginning. search() scans entire string finding first match anywhere. match() like ^pattern, search() finds pattern. Example: match(r'\d', 'a1') returns None, search(r'\d', 'a1') finds '1'. Use match for validation, search for finding.

Use urllib.request.urlopen(url) for HTTP GET. Returns response object. Example: with urlopen('http://example.com') as r: data = r.read(). Basic HTTP client. requests library more feature-rich.

Python exponentiation operator is ** (double asterisk). Example: 2**3 equals 8 (2 to power 3). Alternative: pow(2,3). Performs power/exponentiation calculation. Higher precedence than multiplication. Right-associative: 2**2**3 equals 2**(2**3)=256. Note: PHP uses ** too (PHP 5.6+).

Use math.sin(), math.cos(), math.tan() for trigonometry. Arguments in radians. Example: math.sin(math.pi/2) = 1.0. math.radians() converts degrees. math.degrees() converts to degrees. Trig functions.

Output: \nthing (literal backslash-n). Raw string r'' treats backslashes literally. No escape sequence interpretation. \n prints as two characters not newline. Raw strings useful for regex, file paths. r prefix disables escape processing. Literal backslash output.