Python

20-hour Pareto plan targeting Python for backend development and data processing roles. Session 1 anchors the mental model; subsequent sessions build from core language features to concurrency, testing, and ecosystem. Python Mental Model: Objects, Names, and Scope Python's execution model differs fundamentally from many other languages. Understanding it prevents an entire class of subtle bugs. Everything is an Object In Python, everything — integers, functions, classes, modules — is an object with an identity (), a type (), and a value. Names, Not Variables Python has names that bind to objects, not variables that contain values. Assignment creates a binding, not a copy. LEGB Scope Rule Python resolves names in this order: Local → Enclosing → Global → Built-in Python's Data Model: Mutable vs Immutable Interview Q&A Q: What is the difference between and in Python? A: compares values (calls ). compares identity — whether two names refer to the exact same object in memory (). For small integers (-5 to 256) and interned strings, Python caches objects, so may return even for literals. Always use for value comparison; use only for checks (). Q: Why should you never use a mutable default argument? A: Default argument values are evaluated once when the function is defined, not each time it's called. A mutable default (like or ) is created once and shared across all calls that don't provide that argument. Mutations in one call persist to the next. Fix: use as default and create the mutable inside the function body. Q: What does Python's function return? A: The memory address of the object (CPython implementation). It's guaranteed to be unique among currently existing objects. After an object is deleted and garbage collected, a new object may get the same id. Use to verify if two names refer to the same object. Common Mistakes Java Implementation