Taking the floor of a float

Question

I have found two ways of taking floors in Python:

3.1415 // 1

and

import math
math.floor(3.1415)

The problem with the first approach is that it return a float (namely 3.0). The second approach feels clumsy and too long.

Are there alternative solutions for taking floors in Python?

Solution 1

As long as your numbers are positive, you can simply convert to an int to round down to the next integer:

>>> int(3.1415)
3

For negative integers, this will round up, though.

Solution 2

You can call int() on the float to cast to the lower int (not obviously the floor but more elegant)

int(3.745)  #3

Alternatively call int on the floor result.

from math import floor

f1 = 3.1415
f2 = 3.7415

print floor(f1)       # 3.0
print int(floor(f1))  # 3
print int(f1)         # 3
print int(f2)         # 3 (some people may expect 4 here)
print int(floor(f2))  # 3

http://docs.python.org/library/functions.html#int

Solution 3

The second approach is the way to go, but there's a way to shorten it.

from math import floor
floor(3.1415)

Solution 4

Beware that taking the floor and casting to an int are not the same thing with negative numbers. If you really want the floor as an integer, you should cast to an int after calling math.floor().

>>> int(-0.5)
0
>>> math.floor(-0.5)
-1.0
>>> int(math.floor(-0.5))
-1

Solution 5

Cast it to int if you don't want a float

int(3.1415 // 1)

View more solutions

Comments

[Karoly Horvath]

pick the second one. nothing wrong with it.

[Thomas Orozco]

You could always call int(3.1415), but rather than a floor, it rounds towards 0, which will yield a different result for numbers <0.

[wim]

uncyclopedia.wikia.com/wiki/Pi_equals_exactly_three

[Stam Kaly]

or you could do int(3.1415 // 1) which works like math.floor

[Randomblue]

Why would people expect 4 for int(f2)?

[Matt Alcock]

Because you may expect it to round to the nearest int not the lower int.

[Sven Marnach]

The OP is using Python 3.x, which isn't quite obvious from the post. In Python 3.x, math.floor() returns an int, so it's not necessary to convert the return value.

[Eugene Yarmash]

floor() returns an integer in python3, but in python2 it returns float.

[Mark Ransom]

@eugeney, I was just pointing out that there was a way to leave off the math. part. I wonder why they didn't complain about getting a float result back from floor in the first place? And thanks for informing me of that change from 2 to 3, I didn't know that one. It makes sense, floor couldn't return an int until arbitrary size integers were interchangeable with normal ints starting in 2.4.

[zezollo]

To get any number (positive as well as negative) to round down, there's still int(n // 1), like int(-3.14 // 1) that gives -4. Of course this is only useful if negative numbers might show up.

[Sven Marnach]

@zezollo Unless you want to confuse readers of your code, using int(math.floor(x)) is preferable over floor division by 1, since it's immediately obvious what it does.