Best Practices
Objectives
In Python as in programming in general, it is important to understand and respect syntactic conventions, at the risk of getting errors or unexpected behavior from the program. In this page, you will find all the best practices to implement as early as possible when writing Python programs.
Indentation
In Python, indentation is crucial. Each code block that follows an if
, elif
, else
, while
, for
, def
, must be indented consistently.
Indeed, it is indentation that determines whether an instruction belongs to the current block or not. You can create indentation using the Tab
key.
- Example 1: correct indentation in an
if
block
x = 10
# Correct indentation
if x > 5:
print("x is greater than 5")
print("This message is part of the 'if' block")
print("This message is outside the 'if' block")
Explanation
The first two print
instructions are indented, so they are part of the if
block.
The last print instruction is not indented, it executes independently of the if
.
- Example 2: incorrect indentation in an
if
block
x = 10
# Incorrect indentation
if x > 5:
print("x is greater than 5")
print("This message is part of the 'if' block") # Bad indentation
Explanation
The second print
instruction is not indented, so it is not part of the if
block. It will therefore be executed, regardless of the value of x > 5
- Example 3: indentation error in nesting
x = 10
y = 5
if x > 5:
print("x is greater than 5")
if y > 3:
print("y is greater than 3") # Bad indentation
Explanations
The second print
instruction is not indented, so it is not part of the if y > 3
block.
Python will return an error, because at least one indented instruction is required after if
, elif
, else
, while
, for
, def
instructions.