Truncate and round all elements of a list to 8 characters

I would use f-strings for string formatting. As the other user already answered check for the type:

• using isinstance() builtin function
• a custom defined function is_float(s) that returns True if value or string can be converted to float (without exception).

Then you can left-pad to a fixed-width string of 8 characters with the format literal :8 and even round-up to an integer representation with 0 decimal places using :.0f. Or use both combined: :8.0f - all inside the curly-braces appended to the expression to format (here: d or converted float(d)):

f"{float(d):8.0f}" if isinstance(d, float) or is_float(d) else f"{d:8}"

Including a bit debug-prints at the beginning:

import math data = [12452, "too much characters", 0.12457544512, -0.12457544512, "-1245154.8"] print(f"input: {data}") print(f"dt: {[type(d) for d in data]}") def is_float(s): try: float(s) except ValueError: return False return True processedData = [] for d in data: processedValue = f"{float(d):8.0f}" if isinstance(d, float) or is_float(d) else f"{d:8}" print(processedValue) if len(processedValue) > 8 and '.' in processedValue: decIndex = processedValue.index(".") processedValue = str(round(float(processedValue), 8 - (decIndex + 1))) elif len(processedValue) > 8: processedValue = processedValue[:8] processedData.append(processedValue.rjust(8, " ")) print(f"output: {processedData}") 

Prints as final line the expected:

input: [12452, 'too much characters', 0.12457544512, -0.12457544512, '-1245154.8'] dt: [<class 'int'>, <class 'str'>, <class 'float'>, <class 'float'>, <class 'str'>] 12452 too much characters 0 -0 -1245155 output: [' 12452', 'too much', ' 0', ' -0', '-1245155'] 

See also:

• How to truncate a string using str.format in Python?