2. Indentation

2.1. Python Indentation

Python uses indentation to indicate a block of code for selection and iteration and definition.
Indentation refers to the spaces at the beginning of a code line.
The number of spaces is flexible, but is usually 4 spaces for each indentation.
A tab press can be used instead of 4 spaces, with editors converting the tab to 4 spaces.
Errors result from not using the same number of spaces in the same block of code or for not applying indentation in blocks after a colon (:).

Indentation is required in any block of code where the header line starts with a keyword: (if, elif, else, for, while, def, class, try, except, finally, with) and ends with a colon (:).

Code examples showing indentation:

dice = "5"
if dice == "6":
    print("Win")
elif dice == "1":
    print("Loose")
else:
    print("Roll again.")

for x in "banana":
    print(x)

i = 10
while i > 0:
    print(i)
    i -= 1
print("Go.")

def my_function():
    print("Hello from a function")

Blocks of code nested within other blocks of code need to be indented to the same level of nesting.

num = 3
if num < 0:
    print("Negative number")
else:
    if num == 0:
        print("Zero")
    else:
        print("Positive number")

for x in "ABC":
    for y in "123":
        print(x, y)

2.2. Indenting with Conditionals

Question: The following sequence of code is supposed to check if a number is positive, negative, or zero, but it has indentation errors. Fix the indentation.

n= 10
if n > 0:
print("Positive")
elif n < 0:
print("Negative")
else:
print("Zero")

Solution:

n= 10
if n > 0:
    print("Positive")
elif n < 0:
    print("Negative")
else:
    print("Zero")

2.2.1. Practice Questions

Tasks

The following code is supposed to check if a number is positive, but it has indentation errors. Fix the indentation.
n = 5 if n > 0: print("Positive")
The following code is supposed to check if a number is even or odd, but it has indentation errors. Fix the indentation.
n = 4 if n % 2 == 0: print("Even") else: print("Odd")
The following code is supposed to check if a number is positive, negative, or zero, but it has indentation errors. Fix the indentation.
n = 0 if n > 0: print("Positive") elif n < 0: print("Negative") else: print("Zero")
The following code is supposed to check if a number is positive and even, but it has indentation errors. Fix the indentation.
n = 6 if n > 0: if n % 2 == 0: print("Positive and even")

The following code is supposed to check if a number is positive, negative, or zero, and if it is even or odd, but it has indentation errors. Fix the indentation.

n = -3
if n > 0:
if n % 2 == 0:
print("Positive and even")
else:
print("Positive and odd")
elif n < 0:
if n % 2 == 0:
print("Negative and even")
else:
print("Negative and odd")
else:
print("Zero")

2.3. Indenting with Loops

Question: The following code is supposed to print each character in the string “hello”, but it has indentation errors. Fix the indentation.

for char in "hello":
print(char)

Solution:

for char in "hello":
    print(char)

2.3.1. Practice Questions

Tasks

The following code is supposed to print each character in the string “goodbye”, but it has indentation errors. Fix the indentation.
for char in "goodbye": print(char)
The following code is supposed to print each item in the list [1, 2, 3, 4, 5], but it has indentation errors. Fix the indentation.
numbers = [1, 2, 3, 4, 5] for num in numbers: print(num)
The following code is supposed to print numbers from 1 to 5 using the range function, but it has indentation errors. Fix the indentation.
for i in range(1, 6): print(i)
The following code is supposed to print even numbers from 1 to 10, but it has indentation errors. Fix the indentation.
```
for i in range(1, 11):
if i % 2 == 0:
print(i)
```
The following code is supposed to print a 3x3 grid of numbers, but it has indentation errors. Fix the indentation.
for i in range(1, 4): for j in range(1, 4): print(i * j, end=" ") print()

2.4. Indenting with Functions

Question: The following function is supposed to print a greeting message, but it has indentation errors. Fix the indentation.

def greet(name):
print(f"Hello, {name}!")

Solution:

def greet(name):
    print(f"Hello, {name}!")

2.4.1. Practice Questions

Tasks

The following function, which adds two numbers, has indentation errors. Fix the indentation.
def add_numbers(a, b): result = a + b return result
The following function, which checks whether a number is even or not, has indentation errors. Fix the indentation.
def check_even(number): if number % 2 == 0: return True else: return False
The following function, which sums a list of numbers, contains indentation errors. Fix the indentation.
def sum_list(numbers): total = 0 for num in numbers: total += num return total

The following function, which categorizes an age into one of three categories, has indentation errors. Fix the indentation.

def categorize_age(age):
if age < 13:
category = 'Child'
elif age < 20:
category = 'Teenager'
else:
category = 'Adult'
return category

The following function, which returns the maximum number in a list, has indentation errors. Fix the indentation.

def find_max(numbers):
max_num = numbers[0]
for num in numbers:
if num > max_num:
max_num = num
return max_num