The range() Function in Python

The range() function is a built-in Python function that generates a sequence of numbers. It’s commonly used in for loops to iterate a specific number of times.

Basic Syntax

There are three ways to use range():

1. range(stop)
2. range(start, stop)
3. range(start, stop, step)

1. range(stop) – One Parameter Form

Generates numbers from 0 up to (but not including) the stop value.

python

for i in range(5):
    print(i)

Output:

text

0
1
2
3
4

2. range(start, stop) – Two Parameter Form

Generates numbers from start up to (but not including) stop.

python

for i in range(3, 7):
    print(i)

Output:

text

3
4
5
6

3. range(start, stop, step) – Three Parameter Form

Generates numbers from start to stop, incrementing by step each time.

python

for i in range(0, 10, 2):
    print(i)

Output:

text

0
2
4
6
8

Negative Step

You can count backwards by using a negative step:

python

for i in range(5, 0, -1):
    print(i)

Output:

text

5
4
3
2
1

Important Characteristics

1. Memory Efficient: range() doesn’t create a list in memory – it generates numbers on demand.
2. Not Inclusive: The stop value is never included in the sequence.
3. Immutable Sequence: The sequence produced by range() cannot be modified.

Converting to a List

You can convert a range to a list to see all values:

python

numbers = list(range(1, 6))
print(numbers)  # Output: [1, 2, 3, 4, 5]

Common Use Cases

1. Looping a specific number of times:

python

for _ in range(3):
    print("Hello!")

2. Generating indices for sequences:

python

colors = ['red', 'green', 'blue']
for i in range(len(colors)):
    print(i, colors[i])

3. Creating mathematical sequences:

python

squares = [x**2 for x in range(10)]

Remember that range() creates a sequence of integers, so it’s not suitable for floating-point ranges. For that, you might use NumPy’s arange() or manually increment values in a loop.

For Loops in Python

A for loop in Python is used to iterate over a sequence (like a list, tuple, dictionary, set, or string) or other iterable objects. Here’s a basic explanation with simple examples:

Basic Syntax

python

for item in sequence:
    # code to execute for each item

Example 1: Looping through a list

python

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

Output:

text

apple
banana
cherry

Example 2: Looping through a string

python

for char in "hello":
    print(char)

Output:

text

h
e
l
l
o

Example 3: Using range() function

python

# Prints numbers 0 to 4
for i in range(5):
    print(i)

Output:

text

0
1
2
3
4

Example 4: Looping with index and value

python

colors = ["red", "green", "blue"]
for index, color in enumerate(colors):
    print(f"Index {index} has color {color}")

Output:

text

Index 0 has color red
Index 1 has color green
Index 2 has color blue

Example 5: Nested for loops

python

for i in range(3):
    for j in range(2):
        print(f"i={i}, j={j}")

Output:

text

i=0, j=0
i=0, j=1
i=1, j=0
i=1, j=1
i=2, j=0
i=2, j=1

Example 6: Looping with else clause

python

for num in range(3):
    print(num)
else:
    print("Loop completed!")

Output:

text

0
1
2
Loop completed!

Key Points:

• The for loop executes a block of code for each item in the sequence
• You can use break to exit the loop early
• You can use continue to skip to the next iteration
• The else clause executes after the loop completes normally (not when broken)