How Do I Truncate a Float to a Specific Number of Decimal Places Without Rounding?

How to Remove Digits from a Float

To remove digits from a float and retain a specific number of digits after the decimal point, follow these steps:

Implementation (Python 2.7 and 3.1 ):

def truncate(f, n):
    """Truncates/pads a float f to n decimal places without rounding"""
    s = '{}'.format(f)
    if 'e' in s or 'E' in s:
        return '{0:.{1}f}'.format(f, n)
    i, p, d = s.partition('.')
    return '.'.join([i, (d+'0'*n)[:n]])

Implementation (Older Versions of Python):

def truncate(f, n):
    """Truncates/pads a float f to n decimal places without rounding"""
    s = '%.12f' % f
    i, p, d = s.partition('.')
    return '.'.join([i, (d+'0'*n)[:n]])

Explanation:

1. Convert to String: Convert the float to a string at full precision using '{}'.
2. Handle Scientific Notation: If the string representation includes 'e' or 'E', use '{0:.{1}f}' to format it.
3. Split String: Partition the string into three parts: before the decimal point (i), the decimal point itself (p), and after the decimal point (d).
4. Truncate or Pad: Append '0's to d if necessary to obtain n decimal places, or truncate d if it contains more than n decimal places.

Special Considerations:

• Precision Considerations: For older versions of Python (up to 2.6 or 3.0), selecting a fixed precision (e.g., 12) for rounding may be necessary to avoid truncation errors.
• Rounding and Floating-Point Error: Some floating-point literals may represent the same binary value even though they appear different in code, leading to potential discrepancies in truncation.

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