Python Basics Part 5: Random Numbers, f-Strings, and Input/Output Explained

Python Basics – Part 5: Random Numbers, String Formatting, and Input/Output

In this lesson from my 5-week Python training series, we’ll explore three practical topics that bring programs to life:
random number generation, formatted strings (f-strings), and user input/output.
We’ll also end with an introduction to data visualization using Matplotlib.

Random Numbers in Python

Python’s random module provides a variety of functions for generating pseudo-random numbers.
Let’s start with the basics.

random()

Returns a float between 0 (inclusive) and 1 (exclusive).

from random import random

number = random()
print(number)

Example Output:

0.453443

randint(a, b)

Returns an integer between a and b (both inclusive).

from random import randint

print(randint(1, 6))  # simulating a dice roll

Example Output:

3

Repeated Random Rolls

for _ in range(5):
    print(randint(1, 6), end=' ')

Output:

5 2 6 1 3

Advanced Random Functions

You can import multiple functions at once:

from random import uniform, randrange, choice, sample, seed, gauss

uniform(a, b)

Returns a float between a and b.

print(uniform(2.222, 2.223))

Output:

2.22245685

randrange(start, stop, step)

Similar to range() but returns one random integer.

print(randrange(100, 201, 2))
print(randrange(1, 49 + 1))

choice(sequence)

Picks one random element from a list, tuple, or string.

print(choice([3, 6, 12, 18, 23, 42]))
print(choice(['ABC', 'DEF', 'GHI']))
print(choice('ABCDEFG'))

sample(sequence, k)

Returns a list of k unique elements.

print(sample('ABCDEFGKLMNOPRS', 3))

Output:

['C', 'R', 'D']

seed()

Sets the starting point for random number generation.
Using the same seed always produces the same sequence — helpful for testing.

from random import seed, randint

seed(42)
print(randint(1, 6))  # 6
print(randint(1, 6))  # 1
print(randint(1, 6))  # 1

Note:
Computers use pseudo-random algorithms — not truly random, but unpredictable enough for most applications.

gauss(mu, sigma)

Generates random numbers following a Gaussian (normal) distribution.

from random import gauss

mean = 100      # expected value
stdev = 50      # standard deviation

print(gauss(mean, stdev))

Example Output:

98.01132723714748

Bonus: Visualizing Random Data with Matplotlib

You can plot Gaussian-distributed data using the Matplotlib library.

# To install matplotlib, run this in your terminal:
# pip install matplotlib

import matplotlib.pyplot as plt
from random import gauss

mean = 100
stdev = 50

values = [gauss(mean, stdev) for _ in range(10_000)]

plt.hist(values, bins=100)
plt.title("Gaussian Distribution Example")
plt.xlabel("Value")
plt.ylabel("Frequency")
plt.show()

Note:
If you get an interpreter or import error, make sure you’ve installed Matplotlib and that your Python environment/interpreter is properly configured (e.g., in PyCharm: check File > Settings > Project Interpreter).

String Formatting (f-Strings)

Introduced in Python 3.6, f-strings are a concise way to embed variables or expressions directly in strings.

first_name = "Peter"
last_name = "Wellert"

output = f"My name is {first_name} {last_name}!"
print(output)

Output:

My name is Peter Wellert!

String Concatenation (Old Way)

output2 = "My name is " + first_name + " " + last_name + "!"
print(output2)

Expressions Inside f-Strings

You can include calculations directly inside {}:

a = 7
b = 8
print(f"The product is: {a * b}")

Output:

The product is: 56

Number Formatting

Format floats with a specific number of decimal places:

value = 1 / 6
print(f"Euro: {value:.2f}")

Output:

Euro: 0.17

Add thousands separators:

big_number = 12345.6789
print(f"{big_number:,.2f}")

Output:

12,345.68

Conditional Expressions in f-Strings

name = "Alex"
age = 20
print(f"{name} is {'an adult' if age >= 18 else 'a minor'}.")

Output:

Alex is an adult.

Input and Output

Output with print()

You can print multiple values separated by commas.

print(1, 2, "Three", 4)

Output:

1 2 Three 4

Custom Separators and End Characters

sep controls how printed items are separated.
end defines what is printed at the end (default is \n).

print(1, 2, 3, 4, sep="-")
print(1, 2, 3, 4, sep=", ")
print(1, end="---")
print(2)

Output:

1-2-3-4
1, 2, 3, 4
1---2

---

Line Breaks with \n

print("Hello\nWorld!")

Output:

Hello
World!

User Input with input()

input() pauses the program and waits for the user’s response.

name = input("Please enter your name: ")
print("Hello,", name)

All inputs are strings by default:

print(type(name))  # <class 'str'>

Convert to numbers if needed:

age = int(input("Enter your age: "))
print(f"Next year, you’ll be {age + 1}.")

Summary

In this lesson, we covered:

• Random number functions: random(), randint(), uniform(), choice(), sample(), seed(), gauss()
• String formatting with f-strings and advanced numeric formats
• Input/output operations (print(), input(), sep, end)
• Visualizing random data using Matplotlib

Next up: Type conversion, lists, and basic data structures in Python!