Python - random.seed( ) method

The random.seed() method in Python is used to initialize the random number generator so that it produces the same sequence of random numbers every time a program is run. By setting a fixed seed value, randomness becomes reproducible, which is essential for debugging, testing and scientific experiments.

• Ensures consistent results across multiple executions
• Helps in debugging and verifying program output
• Supports reproducible experiments in machine learning and simulations
• Useful for controlled randomness in game development and testing

Let's understand with an example.

import random
for i in range(2):
    print(random.randint(1, 1000))

for i in range(2):
    random.seed(0)
    print(random.randint(1, 1000))

21
537
865
865

Explanation: Notice that generating random numbers without using the .seed() method results in different outputs on each run, whereas using it ensures consistent results every time.

Syntax

random.seed(a=None, version=2)

Parameters

• a (Optional): it's the seed value (integer, float, str, bytes or bytearray). If None, the system time is used.
• version(Optional): defaults value is 2, using a more advanced seeding algorithm. version=1 uses an older method.

Return Type

random.seed() method does not return any value.

Let's look at some of the examples.

Reproducing Same Random Lists

We can produce the same random list for multiple executions using random.seed() method.

import random

random.seed(9)
print(random.sample(range(1, 50), 6))

[30, 40, 24, 18, 9, 12]

Explanation:

• random.seed(9) sets the seed value to 9. It ensures that random values generated are same for every run.
• random.sample(range(1,50), 6) creates a sequence of numbers from 1 to 49 and randomly selects 6 unique numbers from it.

Reproducible Data Splitting

In machine learning, we often split data into training and testing sets. Using a seed ensures that the split remains the same across multiple runs.

import random
a = list(range(10))
random.seed(10)
random.shuffle(a)
print(a)

[5, 2, 7, 1, 8, 4, 3, 6, 0, 9]

Explanation:

• list(range(10) gives us a list of integers from 0 to 9.
• random.seed(10) sets the seed to 10 ensuring consistant results in each run.
• random.shuffle(a) shuffles the list 'a' randomly but because of the seed() method we get the same shuffled list every time.