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What does Python's `//`

operator do?
How is it different from the `/`

operator?

`/`

operatorThe `/`

operator is the division operator in Python.

When `/`

is used between two numbers, you'll always get the exact (as exact as Python can manage) result back:

```
>>> 5 / 2
2.5
```

Unlike some programming languages, `/`

in Python does not act any differently when used between integers; in Python 3 that is.
In Python 2, division between two integers would would the result downward to the nearest integer:

```
>>> 5 / 2 # Python 2
2
```

But in Python 3, division between two integers **always returns a floating point number** with the exact result:

```
>>> 4 / 2
2.0
```

`//`

operator between integersThe `//`

operator is the floor division operator in Python.
When `//`

is used between two integers, you'll always get an integer back:

```
>>> 5 // 2
2
```

The `//`

operator provides divides while rounding the result down to the nearest integer.
This is often called **integer division** or **floor division**.

When using `//`

with a floating point number, you'll get a floating point number back:

```
>>> 5.0 // 2
2.0
```

But, just as with integers, that floating point number will *also* be **rounded down to the nearest integer**.

`//`

in Python?If you've ever seen code like this:

```
>>> n = 5
>>> int(n / 2)
2
```

Then you've likely witnessed an opportunity to use the `//`

operator.
If you're dividing and then immediately converting the result to an integer, you could probably use the `//`

operator instead.

In this `split_in_half`

function, we're using the `int`

function to make sure the `mid_point`

value is an integer:

```
def split_in_half(sequence):
"""Return two halves of given sequence (list, string, etc)."""
mid_point = int(len(sequence) / 2)
return sequence[:mid_point], sequence[mid_point:]
```

The numbers we're dividing are both integers, so we could use `//`

to force an integer result:

```
def split_in_half(sequence):
"""Return two halves of given sequence (list, string, etc)."""
mid_point = len(sequence) // 2
return sequence[:mid_point], sequence[mid_point:]
```

This is a bit more efficient than dividing to get an exact floating point number and then flooring that floating point number to get back to an integer.

`//`

always rounds downBefore you go about replacing all the uses of `int(a / b)`

in your code with `a // b`

, you should note that these two act differently when the result of the division is a negative number:

Let's say we divide and the result is `-2.5`

:

```
>>> a = -5
>>> b = 2
>>> a / 2
-2.5
```

When using `/`

and `int`

, we'll end up with `-2`

but when dividing with `//`

we'll get `-3`

instead:

```
>>> int(a / 2)
-2
>>> a // 2
-3
```

The `//`

operator **always rounds down**.
It acts less like the built-in `int`

function and more like `math.floor`

:

```
>>> from math import floor
>>> floor(a / 2)
-3
>>> a // 2
-3
```

Also remember that `a // b`

returns a floating point number when either `a`

or `b`

are floating point numbers.

```
>>> a = 52.0
>>> b = 4
>>> a // b
13.0
```

So you'll most likely want to stick to using `//`

only for **division between positive integers**.

`divmod`

insteadWhat if you want both integer division (with `//`

) and the remainder of that division (with `%`

):

```
>>> duration = 500
>>> minutes = duration // 60
>>> seconds = duration % 60
>>> print(f"{minutes}:{seconds}")
8:20
```

Instead of using `//`

and `%`

separately, you could use the `divmod`

function to get both results at once:

```
>>> duration = 500
>>> minutes, seconds = divmod(duration, 60)
>>> print(f"{minutes}:{seconds}")
8:20
```

In theory, this could be optimized to perform both operations at once, but in practice CPython doesn't perform that optimization so this is **primarily about readability**.

Sometimes `divmod`

can make for considerably more readable code.
For example here we're using `//`

and `%`

cleverly to get hours, minutes, and seconds:

```
>>> duration = 9907
>>> hours = duration // (60 * 60)
>>> minutes = (duration // 60) % 60
>>> seconds = duration % 60
>>> print(f"{hours}:{minutes:02d}:{seconds:02d}")
2:46:07
```

But we could use `divmod`

twice instead:

```
>>> duration = 9907
>>> minutes, seconds = divmod(duration, 60)
>>> hours, minutes = divmod(minutes, 60)
>>> print(f"{hours}:{minutes:02d}:{seconds:02d}")
2:46:07
```

I find that `divmod`

approach much clearer than the alternative uses of `//`

and `%`

.
If you need both the quotient (to use a math term) and the remainder of your division, consider using `divmod`

.

**Note**: if you're curious about that `:02d`

syntax above, see zero-padding in f-strings.

`//`

for integer divisionFor most uses of division in Python, you'll likely use `/`

because precise answers are often desirable:

```
>>> amount = 67
>>> groups = 9
>>> per_portion = amount / groups
>>> per_portion
7.444444444444445
```

But in rare moments when you want **floor division** (a.k.a. **integer division**) you'll want the `//`

operator.

```
>>> amount = 67
>>> groups = 9
>>> minimum_per_group = amount // groups
>>> minimum_per_group
7
```

If you want both a remainder `%`

and integer division `//`

, also keep Python's `divmod`

function in mind.

```
>>> duration = 784
>>> minutes, seconds = divmod(duration, 60)
>>> print(f"{minutes}m{seconds}s")
13m4s
```

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