# Python math.floor, import math Examples

Use the math.floor function to take floors of numbers. Remove a number's fractional part.**Floor.** With math.floor we reduce a number so that the fractional part is removed. Floor() will make all numbers smaller. Negative values will become more negative.

Math**With floor,** we get integers from floating-point numbers. Floor has no effect on integers. We must "import math" at the top of our programs.

**Initial example.** Here we use math.floor on some numbers. Note that the first number 100 is returned unchanged. Floor() does not modify integers.

**Rounding:** Floor does not round upon the value 100.9. Instead it always reduces the number to be less.

**Python program that uses math.floor**
import math*
# Some numbers to take floors of.
*value0 = 100
value1 = 100.1
value2 = 100.5
value3 = 100.9*
# Take floor of number.
*floor0 = __math.floor__(value0)
print(value0, *":"*, floor0)*
# Take other floors.
*print(value1, *":"*, math.floor(value1))
print(value2, *":"*, math.floor(value2))
print(value3, *":"*, math.floor(value3))
**Output**
100 : 100
100.1 : 100
100.5 : 100
100.9 : 100

**NameError.** Sometimes when writing Python programs I make this error. There is no "floor" in Python. We must use math.floor to use the floor function.

Error**Python program that causes NameError**
number = *78.6**
# This will not work.
*result = floor(number)
**Output**
Traceback (most recent call last):
File "C:\programs\file.py", line 5, in <module>
result = floor(number)
NameError: name 'floor' is not defined

**Negative floors.** With negative numbers, math.floor has the same logical result as with positive ones. Numbers are always reduced. Negative numbers will become more negative.

**Python program that uses math.floor on negative numbers**
import math*
# Use math.floor on a negative number.
*result = __math.floor__(*-1.1*)
print(result)
result = __math.floor__(*-1.9*)
print(result)
**Output**
-2
-2

**Benchmark, floor dictionary.** I wanted to test whether a dictionary lookup could be faster than a math.floor call. I found math.floor is fast—much faster than calling get().

Dictionary**Version 1:** This version of the code uses math.floor to get the floor of each number.

**Version 2:** Here we look up a value in a dictionary to get a cached floor value for a number.

**Result:** Using a dictionary to memoize (cache) the result of math.floor is a big slow down. Just use math.floor directly.

**Python program that benchmarks math.floor, dictionary**
import time, math*
# Floor dictionary.
*floor_dict = {100.5: 100}
print(time.time())*
# Version 1: use math.floor.
*for i in range(0, 100000000):
y = 100.5
z = __math.floor__(y)
if z != 100:
print(z)
break
print(time.time())*
# Version 2: use dictionary lookup, get method.
*for i in range(0, 100000000):
y = 100.5
z = floor_dict.__get__(y)
if z != 100:
print(z)
break
print(time.time())
**Output**
1454633830.142
1454633830.727 math.floor = *0.59 s*
1454633839.844 floor_dict.get = *9.12 s*
PyPy3 used

**A review.** In Python 3 we find many built-in functions like abs and round. With floor, though, we have to use the math module with an import statement.

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