python - What is the difference between '/' and '//' when used for division?

Question

Is there a benefit to using one over the other? In Python 2, they both seem to return the same results:

>>> 6/3
2
>>> 6//3
2

Answer 1

In Python 3.x, 5 / 2 will return 2.5 and 5 // 2 will return 2. The former is floating point division, and the latter is floor division, sometimes also called integer division.

In Python 2.2 or later in the 2.x line, there is no difference for integers unless you perform a from __future__ import division, which causes Python 2.x to adopt the 3.x behavior.

Regardless of the future import, 5.0 // 2 will return 2.0 since that's the floor division result of the operation.

You can find a detailed description at https://docs.python.org/whatsnew/2.2.html#pep-238-changing-the-division-operator

Answer 2

Python 2.x Clarification:

To clarify for the Python 2.x line, / is neither floor division nor true division.

/ is floor division when both args are int, but is true division when either of the args are float.

Answer 3

// implements "floor division", regardless of your type. So 1.0/2.0 will give 0.5, but both 1/2, 1//2 and 1.0//2.0 will give 0.

See https://docs.python.org/whatsnew/2.2.html#pep-238-changing-the-division-operator for details

Answer 4

/ --> Floating point division

// --> Floor division

Lets see some examples in both python 2.7 and in Python 3.5.

Python 2.7.10 vs. Python 3.5

print (2/3)  ----> 0                   Python 2.7
print (2/3)  ----> 0.6666666666666666  Python 3.5

Python 2.7.10 vs. Python 3.5

  print (4/2)  ----> 2         Python 2.7
  print (4/2)  ----> 2.0       Python 3.5

Now if you want to have (in python 2.7) same output as in python 3.5, you can do the following:

Python 2.7.10

from __future__ import division
print (2/3)  ----> 0.6666666666666666   #Python 2.7
print (4/2)  ----> 2.0                  #Python 2.7

Where as there is no differece between Floor division in both python 2.7 and in Python 3.5

138.93//3 ---> 46.0        #Python 2.7
138.93//3 ---> 46.0        #Python 3.5
4//3      ---> 1           #Python 2.7
4//3      ---> 1           #Python 3.5

Answer 5

As everyone has already answered, // is floor division.

Why this is important is that // is unambiguously floor division, in all Python versions from 2.2, including Python 3.x versions.

The behavior of / can change depending on:

• Active __future__ import or not (module-local)
• Python command line option, either -Q old or -Q new

Answer 6

>>> print 5.0 / 2
2.5

>>> print 5.0 // 2
2.0

Answer 7

Python 2.7 and other upcoming version of python:

• Division (/)

Divides left hand operand by right hand operand

Example: 4 / 2 = 2

• Floor Division (//)

The division of operands where the result is the quotient in which the digits after the decimal point are removed. But if one of the operands is negative, the result is floored, i.e., rounded away from zero (towards negative infinity):

Examples: 9//2 = 4 and 9.0//2.0 = 4.0, -11//3 = -4, -11.0//3 = -4.0

Both / Division and // floor division operator are operating in similar fashion.

Answer 8

The double slash, //, is floor division:

>>> 7//3
2

Answer 9

// is floor division, it will always give you the integer floor of the result. The other is 'regular' division.

Answer 10

The answer of the equation is rounded to the next smaller integer or float with .0 as decimal point.

>>>print 5//2
2
>>> print 5.0//2
2.0
>>>print 5//2.0
2.0
>>>print 5.0//2.0
2.0

Answer 11

The above answers are good. I want to add another point. Up to some values both of them result in the same quotient. After that floor division operator (//) works fine but not division (/) operator:

>>> int(755349677599789174 / 2) # wrong answer
377674838799894592

>>> 755349677599789174 // 2     # correct answer
377674838799894587

Answer 12

• // is floor division, it will always give you the floor value of the result.
• And the other one / is the floating-point division.

Followings are the difference between / and //; I have run these arithmetic operations in Python 3.7.2

>>> print (11 / 3)
3.6666666666666665

>>> print (11 // 3)
3

>>> print (11.3 / 3)
3.7666666666666667

>>> print (11.3 // 3)
3.0

Answer 13

Python 3.x Clarification

Just to complement some previous answers.

It is important to remark that:

a // b

• Is floor division. As in:

  math.floor(a/b)

• Is not int division. As in:

  int(a/b)

• Is not round to 0 float division. As in:

  round(a/b,0)

As a consequence, the way of behaving is different when it comes to positives an negatives numbers as in the following example:

1 // 2 is 0, as in:

math.floor(1/2)

-1 // 2 is -1, as in:

math.floor(-1/2)

Answer 14

Python 3

Operation	Result	Notes
x / y	quotient of x and y
x // y	floored quotient of x and y	(1)

Notes:

1. Also referred to as integer division. The resultant value is a whole integer, though the result’s type is not necessarily int. The result is always rounded towards minus infinity: 1//2 is 0, (-1)//2 is -1, 1//(-2) is -1, and (-1)//(-2) is 0.

Python 2

Operation	Result	Notes
x / y	quotient of x and y	(1)
x // y	(floored) quotient of x and y	(4)(5)

Notes:

1. For (plain or long) integer division, the result is an integer. The result is always rounded towards minus infinity: 1/2 is 0, (-1)/2 is -1, 1/(-2) is -1, and (-1)/(-2) is 0. Note that the result is a long integer if either operand is a long integer, regardless of the numeric value.

4. Deprecated since version 2.3: The floor division operator, the modulo operator, and the divmod() function are no longer defined for complex numbers. Instead, convert to a floating point number using the abs() function if appropriate.

5. Also referred to as integer division. The resultant value is a whole integer, though the result’s type is not necessarily int.

Answer 15

5.0//2 results in 2.0, and not 2 because the return type of the return value from // operator follows python coercion (type casting) rules.

Python promotes conversion of lower datatype (integer) to higher data type (float) to avoid data loss.