Python random.choices() Function: Usage and Examples

Draw several random selections with replacement and optional weights.

What It Does and Why It Matters

random.choices(population, weights=None, *, cum_weights=None, k=1) returns a list of k selections. Values may repeat; weights need not sum to one, but their total must be positive and finite. cum_weights expresses cumulative totals and cannot be combined with weights.

A weighted draw does not guarantee any exact frequency in a small sample.

Pseudorandom examples are suitable for simulation and tests. Use secrets instead for tokens, passwords and authentication.

Step-by-Step Example

Start with the complete example below. Read the inputs and predict what the final print statement will show before you run it.

import random
number_generator = random.Random(23)
selected_rewards = number_generator.choices(['small', 'large'], weights=[4, 1], k=6)
print(len(selected_rewards))
print(set(selected_rewards) <= {'small', 'large'})

How the Code Works

The imports make these standard-library tools available: random.
The name number_generator receives the value of random.Random(23). Changing this input lets you explore a different case.
The print calls display the results. Compare these results with the method’s documented return type and the input used.
The dedicated Random instance isolates the generator state from unrelated random calls. A fixed seed is useful here for repeatable demonstrations but must not be reused to generate secrets.

Expected output:

6
True

Each displayed line comes from the corresponding calculation or check. The output helps verify the return values before you adapt the example to your own input.

What to Notice

Pay attention to the accepted input types, the returned value and the boundary behavior. Predict what changes if you replace the example input with an empty, zero, negative or missing value, where that value is meaningful for this operation.

If the task uses a library function, inspect its documented exceptions and return type before reusing it inside a larger function.

Where You Would Use This

Use this in calculations, data summaries, simulations or validation when the numerical assumptions match the task. Check input domains, units and precision before interpreting a result. A single example output does not prove a statistical conclusion.

Practice Exercise

Sample 100 rewards with unequal weights and count the outcomes.

Before running your edited example, write down the result you expect. Then test at least one valid boundary or deliberately invalid value, using appropriate exception handling where necessary.

Reference: official Python documentation for the complete API contract and version notes.

Common Beginner Mistakes

Assuming choices() samples distinct items or mixing weights with cum_weights.
Overlooking the documented condition: values may repeat; weights need not sum to one, but their total must be positive and finite. cum_weights expresses cumulative totals and cannot be combined with weights.

Key Takeaways

Draw several random selections with replacement and optional weights.
random.choices(population, weights=None, *, cum_weights=None, k=1) returns a list of k selections.
Sample 100 rewards with unequal weights and count the outcomes.
Pseudorandom examples are suitable for simulation and tests. Use secrets instead for tokens, passwords and authentication.