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How to Get the Number of Digits in Integers and Floats in Python

This guide explains how to determine the number of digits in an integer or the length of a float's string representation in Python.

We'll cover the most efficient and Pythonic methods for integers, using math.log10(), and clarify how to handle floats, where we're actually measuring the string representation.

Getting the Number of Digits in an Integer​

The most efficient way to get the number of digits in an integer without converting it to a string is to use the math.log10() function.

import math

def get_integer_length(integer):
    if integer > 0:
        return int(math.log10(integer)) + 1
    elif integer == 0:
        return 1  # Special case: 0 has 1 digit
    else:
        return int(math.log10(-integer)) + 1 # Correctly handles negatives

print(get_integer_length(100))    # Output: 3
print(get_integer_length(12345))  # Output: 5
print(get_integer_length(-1234))  # Output: 4
print(get_integer_length(0))      # Output: 1
  • math.log10(integer): Calculates the base-10 logarithm of the integer. This essentially tells you how many powers of 10 are needed to reach the number.
  • int(...) + 1: We take the integer part of the logarithm and add 1 to get the number of digits. (e.g., log10(100) is 2, and 100 has 3 digits).
  • Handling Zero and Negative Numbers: The function includes:
    • if integer > 0: The core logic for positive numbers.
    • elif integer == 0: return 1: Zero has 1 digit.
    • else: return int(math.log10(-integer)) + 1: For negative numbers, we take the logarithm of the absolute value (-integer). The number of digits is the same, regardless of the sign.

Using String Conversion (Less Efficient)​

While less efficient, you can convert the integer to a string and get its length:

my_int = 1234
my_str = str(my_int)
print(len(my_str))  # Output: 4

my_int = -1234
if my_int < 0:
    result = len(str(my_int)) - 1 # Subtract 1 for negative sign
else:
    result = len(str(my_int))
print(result)
  • str(my_int): Converts the integer to a string.
  • len(my_str): Gets the length of the string (which is the number of digits, plus the sign if negative).
  • Important: If the number is negative, you usually don't want to count the minus sign as a digit. The example code subtracts 1 in this case.

Getting the Length of a Float's String Representation​

When dealing with floats, you're not getting the "number of digits" in the same way as with integers. Floats are stored in a binary format, and their "length" isn't directly meaningful. Instead, you're getting the length of their string representation.

my_float = 3.14
my_str = str(my_float)
print(len(my_str))  # Output: 4 (includes the decimal point)
print(len(my_str.replace('.', ''))) # Output: 3 (without the decimal)
  • To count only the digits without including the decimal separator you can use the replace() method.
my_float = 3.14

if my_float < 0:
    result = len(str(my_float)) - 1
else:
    result = len(str(my_float))
print(result) # Output 4
  • If you need to also count the sign, make sure to add the condition to account for negative numbers.

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