Generating random numbers in Python is a fairly straightforward activity which can be done in a few lines. There maybe many variations which you need to do ranging from decimal places, random numbers between a start and end number, and many more. We’ll go through many useful examples in this article.

The most basic way to generate random numbers in python is with the random library:

import random

num = random.random()

print( f"Random number between 0.0 and 1.0 ={num}\n")

Output as follows:

You’ll see that each time it is run it has a new random number.

Generating the same random number each time and why this matters

Sometimes, you may want to generate some random numbers, but then be able to generate the same random numbers each time. Now this may sound counter intuitive as the whole point of getting random numbers is so that, well, they are random. One scenario where you would like to regenerate the same random numbers is during testing. You may find some unusual behaviour and this is where you may want to replicate that behaviour for which you’l l need the same input. This is where you’d want to generate the same random number and you can do that in python using the seed function from the random library.

The idea behind the seed function is that you can think of it as a specific key which can be used to generate a series of random numbers which stems from a given key. Use a different seed and you’ll generate a different set of random numbers.

See the following example code which generates a random number between 1 and 0:

import random

random.seed(1)

for i in range(1,5):
    num = random.random()
    print( f"Random number between 0.0 and 1.0 ={num}\n")

Output as follows:

No matter how many times it is run, since the seed is the same each time, it generates the same numbers.

Python Random Number Between 1 and 10

Now that we know how to generate random numbers, how do you do it between two numbers? This is easily done in with either randint() for whole numbers or with uniform() for decimal numbers.

import random

num_int = random.randint(1,10)
print( f"Random whole number between 1 and 10 ={num_int}\n")

num_uni = random.uniform(1,10)
print( f"Random decimal number between 1 and 10 ={num_uni}\n")

Python Generate Random Numbers From A Range

Suppose you needed to generate random numbers from a range of data whether that be numbers, names or even a pack of cards. This can be done through selecting the random element in an array by choosing the index randomly. For example, if you had an array of 5 items, then you can randomly chose and index from 0 to 4 (where 0 is the index of the first item).

There is another and shorter way in python which is to use the random.choice() function. If you pass it an array, it will then randomly return one of the elements.

Here’s an example to randomly select a name from a list with both using the index (to show you how it works), and the much most efficient random.choice() library function:

import random

###### Selecing numbers from a range
names_list = [ "Judy", "Harry", "Sarah", "Tom", "Gloria"]

rand_index = random.randint( 0, len(names_list)-1 )

print( f"Randomly selected person 1 is = { names_list[ rand_index] }\n")
print( f"Randomly selected person 2 is = { random.choice( names_list) }\n")

And the output is different each time:

Generate Random String Of Length n in Python

If you want to generate a specific length string (e.g. to generate a password), both the random and the string libraries can come in handy where you can use it to create an easy password generator as follows:

import random, string

###### Create a random password
def generate_password( pass_len=10):
    password = "" 

    for i in range(1,pass_len+1):
        password = password + random.choice( string.ascii_letters + string.punctuation )
    return password

print( f"Password generated = [{ generate_password(10) }] ")

This will output a new password each time between square brackets:

If there are specific characters you want to include or exclude, you can simply replace the string.punctuation with your own list/array of specific characters to be included

Random Choice Without Replacement In Python

Suppose you wanted to randomly select items from a list without repeating any items. For example, you have a list of students and you have to select them in a random order to go first in a specific activity. In many programming languages you may need to generate a random list and remember the previously selected items to prevent any repeated selections. In the random library, there is a function called random.sample() that will do all that for you:

import random

#### Select unique random elements
students = ["John", "Tom", "Paul", "Sarah", "July", "Rachel"]

random_order = random.sample( students, 6)
print(random_order)

This will generate a unique list without repeating any selections:

Generate Date Between Two Dates in Python

In order to generate a date between two dates, this can be done by converting the dates into days first. This can be combined with the random.randint() in addition to the days of the date differences then adding back to the start date:

import random, datetime  

#### Select a random date between two dates: 
d1 = datetime.date( 2013,  2, 26 )
d2 = datetime.date( 2015, 12, 15 )
diff = d2 - d1 
new_date_days = random.randint( 0, diff.days )

print( f"Random date is {   d1 + datetime.timedelta( days=new_date_days ) }")

The output would be as follows:

Generate Random Temporary Filename in Python

A common need is to generate a random filename often for temporary storage. This might be for a log file, a cache file or some other scenario and can be easily done with the similar string generation as above. First a letter should be determined and then the remaining letters can be added with also numbers as well.

import random, string

def generate_random_filename( filename_len=10):
    filename = "" 
    filename = filename + random.choice( string.ascii_lowercase  )

    for i in range(2, filename_len+1):
        filename = filename + random.choice( string.ascii_lowercase + string.digits )
    return filename

print( f"Random filename = [{ generate_random_filename( 10) }.txt]")

Output as follows:

There is in fact a specific python library though that does this which is even simpler:

import tempfile

filename = tempfile.NamedTemporaryFile( prefix="temp_" , suffix =".txt" )

print( f" Temporary filename is [{ filename.name }] ")

Output of the temporary filename generator is:

Conclusion

The random library has many uses from generating numbers to specific strings with a given length for password generation. Typically, these use cases sometimes have specialised libraries as there can be nuances (e.g for passwords, you may not want a repeating sequence which may be possible through random luck) which you can search for through pypi.org. However, many can be created with simple lines of code as demonstrated above. Send comments below or email me to ask further questions.

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