Data Science Python Programming Syllabus

What is a Python dictionary and how is it written?

A mutable, unordered collection of key-value pairs written with curly braces, e.g., {'name': 'Ann', 'age': 30}; keys must be unique and hashable.

What distinguishes a set from a list in Python?

A set is an unordered collection of unique elements (no duplicates) written with curly braces {} or set(); it does not support indexing.

What is indexing, and what index refers to the first and last element of a sequence?

Indexing accesses an element by position; index 0 is the first element and index -1 is the last element.

What does the slice my_list[1:4] return?

Elements at indices 1, 2, and 3 (the stop index 4 is excluded).

What is the syntax for assigning a variable in Python?

variable_name = value; no type declaration is needed because Python is dynamically typed.

What does multiple assignment a, b = 1, 2 do?

It unpacks values, assigning a = 1 and b = 2 simultaneously (tuple unpacking).

What naming convention is recommended for Python variables?

snake_case (lowercase words separated by underscores); names must start with a letter or underscore and cannot be a reserved keyword.

In Python, what does the variable actually store when you write x = [1, 2, 3]?

It stores a reference (pointer) to the list object in memory, not a copy of the object itself.

What is the augmented assignment operator and give an example?

An operator that combines an operation with assignment, e.g., x += 1 is shorthand for x = x + 1.

What is the basic syntax of an if/elif/else statement in Python?

if condition:\n block\nelif other_condition:\n block\nelse:\n block — each clause ends with a colon and its block is indented.

List Python's six comparison operators.

Equal $==$, not equal $\neq$ (!=), greater than $>$, less than $<$, greater-or-equal $\geq$ (>=), and less-or-equal $\leq$ (<=).

What are Python's three logical operators?

and, or, and not, used to combine or negate boolean expressions.

What is the ternary (conditional) expression syntax in Python?

value_if_true if condition else value_if_false, e.g., 'even' if n % 2 == 0 else 'odd'.

Which values are considered 'falsy' in Python?

None, False, zero ($0$, $0.0$), and empty containers (empty string '', [], {}, (), set()); everything else is truthy.

What is the difference between == and is in Python?

== compares whether two values are equal; is compares whether two references point to the same object in memory (identity).

What are the two main loop types in Python and their typical uses?

The for loop iterates over a sequence/iterable; the while loop repeats as long as a condition remains True.

What does range(2, 10, 2) generate?

The sequence 2, 4, 6, 8 — start at 2, stop before 10, step by 2.

What do the break and continue statements do in a loop?

break exits the loop entirely; continue skips the rest of the current iteration and moves to the next one.

What is the purpose of a loop's else clause in Python?

The else block runs after the loop completes normally (i.e., not terminated by a break).

Write the list comprehension that produces the squares of numbers 0 through 4.

[x**2 for x in range(5)], which yields [0, 1, 4, 9, 16].

What keyword defines a function in Python, and what keyword returns a value?

def defines a function; return sends a value back to the caller (a function with no return returns None).

What is the difference between a positional argument and a keyword argument?

A positional argument is matched by order; a keyword argument is matched by name, e.g., func(x=5).

How do you give a function parameter a default value, and why be careful with mutable defaults?

Write it as def f(x=10):. Avoid mutable defaults like def f(x=[]): because the same list is shared across all calls.

What do *args and **kwargs allow in a function definition?

*args collects extra positional arguments into a tuple; **kwargs collects extra keyword arguments into a dictionary.

What is a lambda function in Python?

An anonymous, single-expression function, e.g., square = lambda x: x**2; it returns the expression's value automatically.

What is variable scope, and what does the LEGB rule stand for?

Scope is the region where a name is accessible. LEGB is the lookup order: Local, Enclosing, Global, Built-in.

What is a Python decorator?

A function that takes another function and extends or modifies its behavior, applied with the @decorator syntax above a function definition.

What is a generator function and which keyword creates one?

A function that yields values lazily one at a time using the yield keyword, producing an iterator instead of returning all results at once.

What is the Python Standard Library?

A large collection of modules and packages bundled with Python (e.g., math, os, sys, random, datetime, json) available without separate installation.

How do you compute $\sqrt{16}$ and access $\pi$ using the standard library?

Import the math module: math.sqrt(16) returns $4.0$, and math.pi returns approximately $3.14159$.

What is the difference between import module and from module import name?

import module brings in the whole module (access via module.name); from module import name brings a specific object directly into the namespace.

What is a Python module?

A single .py file containing Python definitions and statements that can be imported and reused in other programs.

What does the if __name__ == '__main__': idiom do in a module?

It runs the indented code only when the file is executed directly, not when it is imported as a module.

What is a Python package, and what file traditionally marks a directory as one?

A package is a directory of related modules; an __init__.py file traditionally marks the directory as a package (optional since Python 3.3 namespace packages).

What is the difference between an absolute import and a relative import?

An absolute import uses the full path from the project root (import mypackage.module); a relative import uses dots relative to the current package (from . import module).

What is the recommended way to open a file so it closes automatically?

Use a with statement (context manager): with open('file.txt') as f: — the file is closed automatically when the block ends.

What are the file modes 'r', 'w', 'a', and 'r+'?

'r' read (default), 'w' write (truncates/creates), 'a' append (adds to end), and 'r+' read and write.

What is the difference between read(), readline(), and readlines()?

read() returns the entire file as one string; readline() returns the next single line; readlines() returns a list of all lines.

What is the difference between text mode and binary mode when opening a file?

Text mode ('t', default) reads/writes str and handles encoding; binary mode ('b', e.g., 'rb') reads/writes raw bytes without decoding.

What methods write data to a file in Python?

f.write(string) writes a single string, and f.writelines(list) writes a list of strings; neither adds newline characters automatically.

Why might you call f.flush() when writing to a file?

To force buffered data to be written to disk immediately, rather than waiting for the buffer to fill or the file to close.

Which standard library module is the modern, object-oriented way to handle file paths?

pathlib, whose Path class provides cross-platform path manipulation (e.g., Path('data') / 'file.txt').

What does os.path.join('folder', 'file.txt') do and why use it?

It joins path components with the correct OS-specific separator, ensuring code works across Windows and Unix systems.

How do you check whether a file or directory exists using the standard library?

Use os.path.exists(path) or, with pathlib, Path(path).exists().

What is the difference between an absolute path and a relative path?

An absolute path specifies the location from the root of the filesystem; a relative path is specified relative to the current working directory.

What is an exception in Python?

An error detected during execution that disrupts the normal flow of the program; if unhandled, it terminates the program with a traceback.

What is the difference between a syntax error and an exception?

A syntax error is detected before execution when the code cannot be parsed; an exception (runtime error) occurs while the program is running.

What is the base class of (almost) all built-in exceptions in Python?

BaseException, though user-defined and most catchable exceptions inherit from Exception.

Name three common built-in exception types and when they occur.

ValueError (right type, wrong value), TypeError (wrong type), and ZeroDivisionError (division by zero). Others include KeyError, IndexError, and FileNotFoundError.

What is the basic try/except syntax for handling an exception?

try:\n risky_code()\nexcept SomeError:\n handle_it() — code in try is attempted, and except catches the named error.

What is the purpose of the else and finally clauses in a try statement?

else runs if no exception occurred in the try block; finally always runs (cleanup), whether or not an exception was raised.

How do you manually trigger an exception in Python?

Use the raise statement, e.g., raise ValueError('invalid input').

How can you catch an exception and access its error message in the except block?

Use as to bind it, e.g., except ValueError as e:, then use str(e) or print(e) to read the message.