What exactly is the function of random seed in python

+7 votes

I am a bit confused on what random.seed() does in Python. For example, why does the below trials do what they do (consistently)?

>>> import random
>>> random.seed(9001)
>>> random.randint(1, 10)
>>> random.randint(1, 10)
>>> random.randint(1, 10)
>>> random.randint(1, 10)
>>> random.randint(1, 10)

I couldn't find good documentation on this. Thanks in advance!

Oct 12, 2018 in Python by charlie_brown
• 7,720 points

8 answers to this question.

+2 votes

Pseudo-random number generators work by performing some operation on a value. Generally this value is the previous number generated by the generator. However, the first time you use the generator, there is no previous value.

Seeding a pseudo-random number generator gives it its first "previous" value. Each seed value will correspond to a sequence of generated values for a given random number generator. That is, if you provide the same seed twice, you get the same sequence of numbers twice.

Generally, you want to seed your random number generator with some value that will change each execution of the program. For instance, the current time is a frequently-used seed. The reason why this doesn't happen automatically is so that if you want, you can provide a specific seed to get a known sequence of numbers.

Hope it works!!

If you are a beginner and need to know more about Python, It's recommended to go for Python Certification course today.


answered Oct 12, 2018 by aryya
• 7,450 points
+4 votes

The seed method is used to initialize the pseudorandom number generator in Python.

The random module uses the seed value as a base to generate a random number. if seed value is not present it takes system current time. if you provide same seed value before generating random data it will produce the same data. 


import random

random.seed( 30 )
print ("first number  - ", random.randint(25,50))  

random.seed( 30 )
print ("Second number- ", random.randint(25,50))


first number - 42
Second  number - 42

answered Oct 29, 2018 by Rahul

Hey @Rahul.. I get the same output when I run your code from a file but when I run the same code in the python console, I get different output. Can you please tell me why is that so?

You need to run random.seed(30) again to set the seed back to its previous value. Generally, the seed is the previous value generated by the generator. So, when you ran random.randint(25,50) second time, your seed was 42 and not 30. 

If you run random.seed(30) again, 42, 50,...will be the sequence of numbers generated.

Suppose I generate 10 values, will all these values be stored? If yes, where are these values stored? Thanks
No. the last value it generated will be stored because that value will work as the seed for next number
import random

for i in range(2):
    for i in range(20):

Use the above code to see a repeated output for yourself

ohh okayyy! Thanks, the example makes it clearer.
+1 vote
We dont really know
answered Mar 16, 2019 by anonymous
+1 vote
Check this link, but basically the seed is a reference to your random number and when you call it it will generate the same random number
answered Apr 16, 2019 by Yordan Ramshev
+1 vote
Random sequence generation starts with reference to the provided seed. So if same seed provided twice same sequence is obtained as the same algorithm works in background.
answered May 4, 2019 by Abhijit Choudhary
Is it like an XOR function? If you use it twice you get the same output again.
+1 vote

The seed() is one of the methods in Python's random module. It initializes the pseudorandom number generator. You should call it before generating the random number. If you use the same seed to initialize, then the random output will remain the same.



import random as r

r.seed( 13 )
print("First iteration  - ", r.randint(2, 40))  

r.seed( 13 )
print("Second iteration - ", r.randint(2, 40))


First iteration  -  18
Second iteration -  18
answered Aug 30, 2019 by Vani sharma
That's a really nice explanation. I've upvoted your answer.
What is 13  in seed(13) ??it indicates what
0 votes

How Does Random Work? Nearly all of the functions in this module depend on the basic random() function, which will generate a random float greater than or equal to zero and less than one. Python uses the Mersenne Twister to generate the floats. It produces 53-bit precision floats with a period of 2**19937-1.

The rand() function is used in C/C++ to generate random numbers in the range [0, RAND_MAX). Note: If random numbers are generated with rand() without first calling srand(), your program will create the same sequence of numbers each time it runs.

answered Dec 11, 2020 by Gitika
• 65,910 points
0 votes

Definition and Usage

The seed() method is used to initialize the random number generator.

The random number generator needs a number to start with (a seed value), to be able to generate a random number.

By default the random number generator uses the current system time.

Use the seed() method to customize the start number of the random number generator.

answered Dec 11, 2020 by Rajiv
• 8,910 points
Thanks for posting useful information.

Thanks, @cyberradarsystems for your contribution

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