Rounding numbers in Python is a common task that can be accomplished using several different methods. One of the most basic ways to round a number down in Python is to use the builtin floor()
function, which is part of the math
module. This function takes a single argument, the number to be rounded down, and returns the largest integer that is less than or equal to the input number.
Here is an example of how to use the floor()
function to round down a number in Python:
import math
# The number to be rounded down
x = 3.14
# Round down x using the floor() function
rounded_x = math.floor(x)
# Print the result
print(rounded_x)
This code will output the integer value 3, which is the largest integer that is less than or equal to 3.14.
Another way to round down a number in Python is to use the builtin int()
function. This function takes a single argument, the number to be rounded down, and converts it to an integer by truncating any decimal places.
Here is an example of how to use the int()
function to round down a number in Python:
# The number to be rounded down
x = 3.14
# Round down x using the int() function
rounded_x = int(x)
# Print the result
print(rounded_x)
This code will also output the integer value 3, which is the largest integer that is less than or equal to 3.14.
You can also use the math.trunc()
to do the same thing as int()
function.
import math
# The number to be rounded down
x = 3.14
# Round down x using the math.trunc() function
rounded_x = math.trunc(x)
# Print the result
print(rounded_x)
In addition to these builtin functions, you can also use the decimal
module to round a number down in Python. The decimal
module provides more precise decimal arithmetic and allows you to control the precision of the result.
Here is an example of how to use the decimal
module to round down a number in Python:
from decimal import Decimal
# The number to be rounded down
x = Decimal('3.14')
# Round down x using the quantize() method of the Decimal class
rounded_x = x.quantize(Decimal('1'), rounding='floor')
# Print the result
print(rounded_x)
This code will also output the integer value 3.
In conclusion, there are multiple ways to round a number down in Python using the builtin math.floor()
, int()
, math.trunc()
functions or decimal
module. All of these methods can be used to round a number down to the nearest integer, but the decimal
module provides more precise decimal arithmetic and allows you to control the precision of the result.
One important thing to note when rounding numbers in Python is that some methods may produce unexpected results when working with negative numbers. For example, the math.floor()
function will round negative numbers down to the next lowest negative integer, while the int()
and math.trunc()
functions will truncate the decimal places and round towards zero.
Here is an example to illustrate this difference:
import math
x = 3.14
# Using math.floor()
rounded_x = math.floor(x)
print(rounded_x) # Output: 4
# Using int()
rounded_x = int(x)
print(rounded_x) # Output: 3
# Using math.trunc()
rounded_x = math.trunc(x)
print(rounded_x) # Output: 3
As you can see, math.floor()
returns 4 while both int()
and math.trunc()
returns 3.
Another important thing to note is that when using the decimal
module, you can also control the precision of the result. By default, the quantize()
method of the Decimal
class rounds to the nearest representable decimal, but you can use the rounding
parameter to specify a different rounding algorithm.
Here is an example of how to use the quantize()
method to round a number down to two decimal places:
from decimal import Decimal
x = Decimal('3.14159')
# Round down x to two decimal places
rounded_x = x.quantize(Decimal('0.01'), rounding='floor')
print(rounded_x) # Output: 3.14
As you can see, the quantize()
method rounds the number down to two decimal places and returns 3.14.
In addition to these functions and modules, Python also has a builtin round()
function which rounds a number to the nearest integer or to a specified number of decimal places. However, it rounds to the nearest even number if the number to be rounded is exactly halfway between two others.
In conclusion, Python provides several ways to round numbers, each with its own behavior and use cases. The math.floor()
function is useful for rounding down to the next lowest integer, while the int()
and math.trunc()
functions are useful for truncating decimal places and rounding towards zero. The decimal
module provides more precise decimal arithmetic and allows you to control the precision of the result. And the round()
function rounds a number to the nearest integer or to a specified number of decimal places but rounds to the nearest even number if the number to be rounded is exactly halfway between two others.
Popular questions

How can I round a number down to the next lowest integer in Python?
Answer: You can use themath.floor()
function to round a number down to the next lowest integer. For example:import math; x = 3.14; rounded_x = math.floor(x); print(rounded_x)
will output 3. 
How can I truncate decimal places and round towards zero in Python?
Answer: You can use theint()
ormath.trunc()
functions to truncate decimal places and round towards zero. For example:x = 3.14; rounded_x = int(x); print(rounded_x)
will output 3. 
How can I control the precision of the result when rounding a number in Python?
Answer: You can use thedecimal
module to control the precision of the result when rounding a number. Thequantize()
method of theDecimal
class allows you to specify the desired precision and rounding algorithm. For example:from decimal import Decimal; x = Decimal('3.14159'); rounded_x = x.quantize(Decimal('0.01'), rounding='floor'); print(rounded_x)
will output 3.14 
How can I round a number to the nearest integer or to a specified number of decimal places in Python?
Answer: You can use the builtinround()
function to round a number to the nearest integer or to a specified number of decimal places. For example:x = 3.14; rounded_x = round(x); print(rounded_x)
will output 3. 
How can I make Python's builtin
round()
function to always round down?
Answer: Python's builtinround()
function rounds to the nearest even number if the number to be rounded is exactly halfway between two others. If you want to always round down, you can subtract a small value from the number before rounding and then add it back. Or use the math.floor() function as mentioned above.
Tag
Rounding