Ch 1 — Variables & Naming

Aryan wants to build a tool that watches his computer’s RAM usage in real time. Before he can read a single byte of memory data, he needs to understand how Python stores and names information. Variables are the foundation — every piece of RAM data the tool tracks will live in one.

Variables

A variable is a named container for a value. In Python you do not declare a type — you just assign and go.

total_ram = 16  # GB
used_ram = 6.4
label = "RAM Manager v0.1"

Python binds the name total_ram to the integer 16. Change the assignment and the binding updates instantly.

total_ram = 32   # upgraded RAM — same name, new value

Comments

Comments explain why, not just what. They start with # and are ignored by the interpreter.

# Total physical RAM installed on this machine (GB)
total_ram = 16

used_ram = 6.4  # updated every second by psutil

Good comments make a RAM manager readable six months later, even at 2 AM during an incident.

Indentation

Python uses indentation (4 spaces per level) instead of braces to define blocks. Mixing tabs and spaces causes IndentationError.

if used_ram > 12:
    print("Warning: RAM usage critical")   # indented block
    print("Consider killing background apps")

Keywords

Keywords are reserved words that Python owns. You cannot use them as variable names.

# BAD — 'if' is a keyword
# if = 10   → SyntaxError

# GOOD
threshold = 10

Common keywords: if, else, for, while, def, class, import, return, True, False, None, and, or, not, in, is.

Identifiers

An identifier is any name you invent — for variables, functions, or classes.

Rules:

• Start with a letter or underscore _
• Contain letters, digits, underscores — no spaces or hyphens
• Case-sensitive: Ram and ram are different names

_internal_counter = 0   # valid — leading underscore
ram2  = 8               # valid — digit after first char
# 2ram = 8              # INVALID — cannot start with digit

Dynamic Typing

Python figures out the type at runtime. The same name can point to different types across assignments.

status = "ok"         # str
status = 200          # now int — Python is fine with this
status = True         # now bool

For the RAM manager this means you can prototype fast, but you should still name variables clearly so the type is obvious from context.

Naming Conventions

MAX_RAM_GB = 16          # constant — won't change at runtime
used_ram_mb = 6553.6     # variable — updated every second
process_name = "chrome"  # descriptive snake_case

Concept Map

flowchart LR
    A[Python Program] --> B[Variables]
    B --> C[Name]
    B --> D[Value]
    D --> E[Integer]
    D --> F[Float]
    D --> G[String]
    D --> H[Boolean]
    C --> I[Naming Rules]
    I --> J[snake_case]
    I --> K[No keywords]
    I --> L[Letters / digits / _]

Variable Lifecycle in the RAM Manager

flowchart TD
    A[Program starts] --> B[total_ram = 16]
    B --> C[used_ram = psutil.read]
    C --> D{used_ram > threshold?}
    D -->|Yes| E[Trigger alert]
    D -->|No| F[Log to file]
    E --> C
    F --> C

Key Takeaways

• Variables bind a name to a value — no type declaration needed.
• Use # for comments; they are ignored at runtime but vital for humans.
• Python enforces indentation as syntax — 4 spaces per level.
• Keywords (if, for, def, …) are off-limits as variable names.
• Python is dynamically typed — the same name can hold different types over time.
• Follow snake_case for variables/functions, SCREAMING_SNAKE for constants, and PascalCase for classes.
• Clear, descriptive names (used_ram_mb vs x) make a RAM manager script self-documenting.