How to multiply in python

How do you multiply in Python?

Short answer: use the * operator. 7 * 3 returns 21. To square a number or raise it to a power, use **: 5 ** 2 returns 25. To multiply all the numbers of a list, use math.prod().

print(7 * 3)                       # 21
print(5 ** 2)                      # 25
 
import math
print(math.prod([1, 2, 3, 4, 5]))  # 120

* multiplies, ** raises to a power, math.prod() multiplies a whole list and a list comprehension multiplies each element.

Every way to multiply in Python

Multiply numbers with the * operator

price = 19
quantity = 3
total = price * quantity
print(total)  # 57

The type of the result depends on the numbers you multiply:

Two integers give an integer. As soon as one of them is a float, the result is a float. Floats can show tiny rounding errors, such as 0.1 * 3 returning 0.30000000000000004. Use round(0.1 * 3, 2) to show 0.3, or the decimal module when you work with money.

To multiply and update a variable at the same time, use *=:

score = 10
score *= 2
print(score)  # 20

Square a number in Python

To square a number, multiply it by itself or raise it to the power of 2. All of these return the square of 5:

import math
import numpy as np
 
print(5 ** 2)          # 25    exponent operator, the most common
print(pow(5, 2))       # 25    built-in function
print(5 * 5)           # 25    the number times itself
print(math.pow(5, 2))  # 25.0  always returns a float
print(np.power([1, 2, 3], 2))  # [1 4 9]  every item of an array

Be careful with negative numbers: -3 ** 2 returns -9, because Python applies ** before the minus sign. Write (-3) ** 2 to get 9. The same operator works for any power: 2 ** 10 is 1024, 2 ** -1 is 0.5 and 9 ** 0.5 is the square root, 3.0.

Multiply all the numbers in a list

math.prod() (Python 3.8 or newer) multiplies every number of a list:

import math
 
nums = [1, 2, 3, 4, 5]
print(math.prod(nums))  # 120

If you can't use it, a loop does the same. Start the result at 1, not 0, or everything will be zero:

result = 1
for n in nums:
    result *= n
print(result)  # 120

With NumPy, use np.prod(nums). With functools, use reduce(lambda x, y: x * y, nums).

Multiply each element of a list by a number

nums = [1, 2, 3]
 
print([n * 3 for n in nums])  # [3, 6, 9]
print(nums * 3)               # [1, 2, 3, 1, 2, 3, 1, 2, 3]

nums * 3 does not multiply the numbers: it repeats the list three times. To multiply each element, use a list comprehension, or a NumPy array:

import numpy as np
 
arr = np.array([1, 2, 3])
print(arr * 3)    # [3 6 9]
print(arr * arr)  # [1 4 9]   element by element

For matrix multiplication with NumPy, use @ (or np.dot()), not *.

Multiply strings and lists

The * operator repeats strings and lists when you multiply them by an integer:

print("ha" * 3)  # hahaha
print("-" * 20)  # --------------------
print([0] * 5)   # [0, 0, 0, 0, 0]

To create a grid, don't write [[0] * 3] * 3: the three rows are the same list, so changing one changes all of them. Use [[0] * 3 for _ in range(3)] instead.

Use AI to check your calculations

An assistant like ChatGPT, Claude or GitHub Copilot can explain an unexpected result if you give it your code and what you expected. These three prompts are ready to copy.

1. Explain a result

In Python, [paste your code] returns [the result] but I expected [what you expected].
Explain why and show me how to fix it.

2. Multiply data

I have this Python list: [paste the list]. Show me how to multiply [all the numbers / each element by X]
with plain Python and with NumPy, and explain which is faster for large lists.

3. Fix a TypeError

I get this error in Python: [paste the error]. This is my code: [paste the code].
Explain what types are being multiplied and how to convert them.

Run every answer yourself and check the result.

Common problems when multiplying in Python

Related guides

• What is a float in Python
• How to round in Python
• Python double slash (//) operator
• How to get the length of a list in Python
• How to comment out multiple lines in Python