Python’s syntax is known for being clean, readable, and highly expressive. In this section, we will cover the fundamental rules you need to follow when writing Python code.

---

1. Indentation rules

Indentation refers to the spaces at the beginning of a code line. Where in other programming languages the indentation in code is for readability only, the indentation in Python is very important.

Python uses indentation to indicate a block of code (like a loop, a function, or conditional statements).

Example of correct indentation:

if 5 > 2:
    print("Five is greater than two!") 

Example of a Syntax Error:

If you omit the indentation, Python will throw an error:

if 5 > 2:
print("Five is greater than two!") # IndentationError: expected an indented block

Important Rules:

• The number of spaces is up to you as a programmer, but it has to be at least one.
• Convention: The standard practice is to use 4 spaces for each indentation level.
• You have to use the same number of spaces in the same block of code, otherwise Python will give you an error.

# Correct
if 5 > 2:
    print("Five is greater than two!")
    print("This is also in the block.")

# Error
if 5 > 2:
    print("Five is greater than two!")
      print("This is also in the block.") # IndentationError

---

2. Comments (single-line, multi-line)

Comments are used to explain Python code, make the code more readable, and prevent execution when testing code.

Single-line Comments

Comments start with a #, and Python will ignore the rest of the line.

# This is a comment
print("Hello, World!") # This is a comment at the end of a line

Multi-line Comments

Python does not really have a distinct syntax for multi-line comments. To add a multiline comment you could insert a # for each line:

# This is a comment
# written in
# more than just one line
print("Hello, World!")

Alternatively, you can use multi-line strings (triple quotes """ or '''). Since Python will ignore string literals that are not assigned to a variable, you can use them as a multi-line comment:

"""
This is a comment
written in
more than just one line
"""
print("Hello, World!")

---

3. Statements and line continuation

Usually, a Python statement ends with a newline. However, Python allows you to write long statements over multiple lines using the line continuation character (\).

Explicit Line Continuation

total = 1 + 2 + 3 + \
        4 + 5 + 6 + \
        7 + 8 + 9

Implicit Line Continuation

Line continuation is implied inside parentheses (), brackets [], and braces {}. This is the preferred method over using the backslash.

# Implicit continuation (preferred)
total = (1 + 2 + 3 +
         4 + 5 + 6 +
         7 + 8 + 9)

days = ['Monday', 'Tuesday', 'Wednesday',
        'Thursday', 'Friday']

---

4. Case sensitivity

Python is a case-sensitive language. This means that variables, functions, class names, and all other identifiers must be typed with the exact same capitalization.

For example, my_variable, My_variable, and MY_VARIABLE are treated as three completely different identifiers.

age = 25
Age = 30
AGE = 35

print(age) # Outputs: 25
print(Age) # Outputs: 30

Also, Python keywords are case-sensitive. You must use if, while, True, False, None exactly as they are defined. Typing IF or true will result in a syntax error.