Python’s multiplication operator `*`

multiplies two objects. The semantics of the multiplication depends on the operands’ data types. For example, multiplying two integers performs arithmetic multiplication whereas multiplying a list with an integer performs list concatenation. The specific return value of the multiplication operator is defined in a data types’ `__mul__()`

magic method.

Have a look at the following examples!

Table of Contents

## Examples

The `*`

operator on integer operands yields another integer—the mathematical product of both operands:

>>> 2 * 2 4 >>> 2 * 3 6 >>> 2 * 4 8 >>> 16 * 16 256

If at least one of the operands is a float value, the result is also a float—float is infectious!

>>> 2.0 * 44 88.0 >>> 4 * 2.2 8.8 >>> 2.2 * -2.2 -4.840000000000001

We can also multiply a string with an integer that performs string concatenation, concatenating the same string *n* times assuming *n* is the second integer operand:

>>> 'boom! ' * 10 'boom! boom! boom! boom! boom! boom! boom! boom! boom! boom! '

In fact, you can multiply other sequence types with integers as well such as lists. The result is the same sequence appended to itself *n* times. The original lists remain unchanged.

>>> [1, 2] * 3 [1, 2, 1, 2, 1, 2] >>> ('Alice', 'Bob') * 5 ('Alice', 'Bob', 'Alice', 'Bob', 'Alice', 'Bob', 'Alice', 'Bob', 'Alice', 'Bob')

What if two operands have an incompatible data type—unlike floats and integers?

>>> 'hello' * 'hi' Traceback (most recent call last): File "<pyshell#11>", line 1, in <module> 'hello' * 'hi' TypeError: can't multiply sequence by non-int of type 'str'

The result of incompatible addition is a `TypeError`

. You can fix it by using only compatible data types for the operation.

Can you use the multiplication operator on custom objects? Yes!

## Python Addition Magic Method

To use the multiplication operator on custom objects, define the `__mul__()`

*“dunder” *or *magic method* that takes two arguments: `self`

and `other`

and returns the result of `self * other`

. The method can use the attributes from the two operand instances.

In the following code, you define the multiplication magic method on a custom data type called `Network`

that quantifies a value of a given network. If you combine two networks, the value multiplies!

class Network: def __init__(self, value): self.value = value def __mul__(self, other): return Network(self.value * other.value) # Create two networks: my_network = Network(2) your_network = Network(4) # Multiply two custom Network instances: our_network = my_network * your_network print(our_network.value) # 8

Consequently, the new Network created by multiplying your network with my network has value 2*4 = 8.

## Python Multiplication Operator Chaining

You can chain together two multiplication operators. For example, the expression

would first multiply **x * y * z**`x`

and `y`

and then multiply z with the result. Thus, it is semantically identical to

.**((x * y) * z)**

Here’s a minimal example:

>>> x = 10 >>> y = 5 >>> z = 2 >>> x * y * z 100 >>> ((x * y) * z) 100

## Arithmetic Operators

Arithmetic operators are syntactical shortcuts to perform basic mathematical operations on numbers.

Operator | Name | Description | Example |
---|---|---|---|

+ | Addition | Calculating the sum of the two operands | `3 + 4 == 7` |

– | Subtraction | Subtracting the second operand from the first operand | `4 - 3 == 1` |

* | Multiplication | Multiplying the first with the second operand | `3 * 4 == 12` |

/ | Division | Dividing the first by the second operand | `3 / 4 == 0.75 ` |

% | Modulo | Calculating the remainder when dividing the first by the second operand | `7 % 4 == 3` |

// | Integer Division, Floor Division | Dividing the first operand by the second operand and rounding the result down to the next integer | `8 // 3 == 2` |

** | Exponent | Raising the first operand to the power of the second operand | `2 ** 3 == 8` |

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