Question

How do I check if a string represents a numeric value in Python?

def is_number(s):     try:         float(s)         return True     except ValueError:         return False 

The above works, but it seems clunky.

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_{If what you are testing comes from user input, it is still a string even if it represents an int or a float. See How can I read inputs as numbers? for converting the input, and Asking the user for input until they give a valid response for ensuring that the input represents an int or float (or other requirements) before proceeding.}

Answer 1

Which, not only is ugly and slow

I’d dispute both.

A regex or other string parsing method would be uglier and slower.

I’m not sure that anything much could be faster than the above. It calls the function and returns. Try/Catch doesn’t introduce much overhead because the most common exception is caught without an extensive search of stack frames.

The issue is that any numeric conversion function has two kinds of results

• A number, if the number is valid
• A status code (e.g., via errno) or exception to show that no valid number could be parsed.

C (as an example) hacks around this a number of ways. Python lays it out clearly and explicitly.

I think your code for doing this is perfect.