Core Syntax, Variables, and Comments

3 min read

1. Python’s Core Syntax: Indentation

Unlike many programming languages that use curly braces ({}) or keywords to define blocks of code (like functions or loops), Python uses whitespace and indentation. This is Python’s most distinctive syntactic feature and is mandatory.

Rule: Code within the same block (e.g., inside an if statement or a function) must be indented by the same amount. The standard is four spaces.
Best Practice: Always use four spaces (not tabs, although some editors can convert tabs to spaces).

Example: Indentation

# The print() statement is inside the if block because it is indented.
if 5 > 2:
    print("Five is greater than two!") 
    print("This is also part of the block.")
    
# This statement is outside the if block.
print("Finished check.")

2. Variables

A variable is a name given to a memory location that stores data. In Python, variables are created the moment you first assign a value to them.

Assignment Operator: The equals sign (=) is used to assign a value to a variable.
Dynamic Typing: You do not need to declare the variable type (e.g., integer, string) before using it. Python figures out the type at runtime.

A. Variable Rules and Conventions

Start Character: Must start with a letter (a-z, A-Z) or an underscore (_).
Case-Sensitive: myVar is different from myvar.
Convention: Use snake_case (lowercase with underscores) for variable names (e.g., user_name, total_price).

B. Variable Reassignment

You can change the value and even the type of a variable at any point.

# Assignment
x = 10 
greeting = "Hello"

# Reassignment (changing the value)
x = x + 5 # x is now 15

# Dynamic Type Change (changing the type)
x = "Now I am a string"

3. Basic Output and Input

A. Output with `print()`

The print() function is used to display output to the console. It can accept variables, values, and combinations thereof.

name = "Charlie"
age = 30
print(name)           # Output: Charlie
print("Age:", age)    # Output: Age: 30

B. Input with `input()`

The input() function allows a program to pause and wait for the user to type in data from the console.

Crucial Note: The input() function always returns the user’s entry as a string (str), even if the user types numbers.

user_name = input("Enter your name: ")
print("Welcome, " + user_name)

# Example of string input for numbers (requires conversion later)
raw_age = input("Enter your age: ") 
# raw_age is currently a string, e.g., "25"

4. Comments and Docstrings

Comments are lines of code that the Python interpreter ignores. They are essential for humans to understand the code’s purpose and logic.

A. Single-Line Comments

Use the hash symbol (#).

# This is a comment, explaining the next line.
result = 42

B. Multi-Line Comments (Docstrings)

Use three double-quotes ("""...""") or three single-quotes ('''...''').
When placed immediately after a function or class definition, these are called docstrings and are used for documentation that can be programmatically accessed.

"""
This is a multi-line comment,
used here as a docstring to explain the file's purpose.
It is standard practice for professional code.
"""
def add(a, b):
    """Adds two numbers and returns the result."""
    return a + b

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