sdf = 12.3456789  # Example float

# Method 1: Using f-strings (Python 3.6+) - Recommended
formatted_sdf = f"{sdf:.3f}"

# Method 2: Using str.format()
formatted_sdf = "{:.3f}".format(sdf)

# Method 3: Using % operator (older style, less preferred)
formatted_sdf = "%.3f" % sdf

# Method 4: Using round() (note: this returns a float, not a string)
rounded_sdf = round(sdf, 3) 
formatted_sdf = str(rounded_sdf) # Convert to string if needed

print(formatted_sdf)  # Output: 12.346 (for all methods except potentially round(), see below)


# Important note about round():
#  - `round()` can sometimes produce slightly unexpected results due to the way floating-point numbers are represented.  
#  - For example, `round(2.675, 2)` returns `2.67` instead of `2.68`. This is because 2.675 cannot be represented exactly in binary. 
#  - If precise rounding to a specific number of decimal places for display is crucial, f-strings or str.format() are generally preferred.


# Example with a list of floats:
sdf_list = [1.2345, 6.7890, 0.000123, 999.9999]

formatted_list = [f"{x:.3f}" for x in sdf_list] # List comprehension with f-strings
print(formatted_list) # Output: ['1.235', '6.789', '0.000', '1000.000']


# Example with a dictionary of floats:
sdf_dict = {"a": 1.2345, "b": 6.7890}
formatted_dict = {key: f"{value:.3f}" for key, value in sdf_dict.items()}
print(formatted_dict) # Output: {'a': '1.235', 'b': '6.789'}

sdf = 12.3456789  # Example value

# Method 1: Using f-strings (Python 3.6+) - generally preferred for readability
formatted_sdf = f"{sdf:.3f}"

# Method 2: Using str.format()
formatted_sdf = "{:.3f}".format(sdf)

# Method 3: Using % operator (older style, less preferred now)
formatted_sdf = "%.3f" % sdf

# Method 4: Using round() (useful if you need the rounded value for calculations, not just display)
rounded_sdf = round(sdf, 3)
formatted_sdf = str(rounded_sdf) # Convert to string for display if needed

print(formatted_sdf)  # Output: 12.346


# Handling potential errors (e.g., if sdf is not a number)

try:
    sdf = float(sdf)  # Attempt to convert to float if it's not already
    formatted_sdf = f"{sdf:.3f}"
    print(formatted_sdf)
except (ValueError, TypeError) as e:
    print(f"Error: Could not format '{sdf}' as a float. {e}")


# Example with a list of numbers:

sdf_list = [1.2345, 45.6789, 0.000123, 999.9999]

formatted_list = [f"{x:.3f}" for x in sdf_list]

print(formatted_list) # Output: ['1.235', '45.679', '0.000', '1000.000']

def format_to_3_decimal_places(sdf):
    """Formats a float or string representing a float to 3 decimal places.

    Args:
        sdf: The float or string to format.

    Returns:
        A string representing the number formatted to 3 decimal places, or the 
        original input if it cannot be converted to a float.
    """
    try:
        num = float(sdf)
        return "{:.3f}".format(num)
    except ValueError:
        return sdf  # Return original input if not a valid float


# Examples
print(format_to_3_decimal_places(12.34567))  # Output: 12.346
print(format_to_3_decimal_places(0.12345))   # Output: 0.123
print(format_to_3_decimal_places(12))        # Output: 12.000
print(format_to_3_decimal_places("123.4"))   # Output: 123.400
print(format_to_3_decimal_places("abc"))     # Output: abc (handles invalid input)
print(format_to_3_decimal_places(12.3455)) # Output: 12.346 (rounding)
print(format_to_3_decimal_places(-12.3455)) # Output: -12.346 (handles negatives)

def format_to_3_decimal_places(sdf):
    """Formats a float or string representing a float to 3 decimal places.

    Args:
        sdf: The float or string to format.

    Returns:
        A string representing the number formatted to 3 decimal places, 
        or the original input if it cannot be converted to a float.
    """
    try:
        num = float(sdf)  # Attempt to convert to float
        return f"{num:.3f}"  # Format to 3 decimal places
    except (ValueError, TypeError):
        return sdf  # Return original input if conversion fails


# Examples
print(format_to_3_decimal_places(12.34567))  # Output: 12.346
print(format_to_3_decimal_places("0.1234"))  # Output: 0.123
print(format_to_3_decimal_places("12"))  # Output: 12.000
print(format_to_3_decimal_places("abc"))  # Output: abc
print(format_to_3_decimal_places(None)) # Output: None




# Alternative using round (less robust, doesn't handle non-numeric inputs as gracefully)

def format_to_3_decimal_places_round(sdf):
    try:
        num = float(sdf)
        return str(round(num, 3))  # Round and convert back to string
    except (ValueError, TypeError):
        return sdf

sdf = 12.3456789  # Example float

# Method 1: Using f-strings (Python 3.6+) - Recommended
formatted_sdf = f"{sdf:.3f}" 

# Method 2: Using str.format()
formatted_sdf = "{:.3f}".format(sdf)

# Method 3: Using % operator (older style, less flexible)
formatted_sdf = "%.3f" % sdf

# Method 4: Using round() and then converting to string (less direct)
formatted_sdf = str(round(sdf, 3))

print(formatted_sdf) # Output: 12.346


# Handling potential errors (e.g., if sdf is not a number)
try:
    formatted_sdf = f"{float(sdf):.3f}" # Convert to float first
except (ValueError, TypeError):
    formatted_sdf = "Invalid input" # Or handle the error appropriately


# For a list of numbers:
numbers = [1.2345, 6.78901, 0.000123, 100]
formatted_numbers = [f"{num:.3f}" for num in numbers]
print(formatted_numbers) # Output: ['1.235', '6.789', '0.000', '100.000']