How to extract a floating number from a string in Python
Question: I have a number of strings similar to `Current Level: 13.4 db.` and I would
like to extract just the floating point number. I say floating and not decimal
as it's sometimes whole. Can RegEx do this or is there a better way?


Answer: If your float is always expressed in decimal notation something like

    
    
    >>> import re
    >>> re.findall("\d+\.\d+", "Current Level: 13.4 db.")
    ['13.4']
    

may suffice.

A more robust version would be:

    
    
    >>> re.findall(r"[-+]?\d*\.\d+|\d+", "Current Level: -13.2 db or 14.2 or 3")
    ['-13.2', '14.2', '3']
    

If you want to validate user input, you could alternatively also check for a
float by stepping to it directly:

    
    
    user_input = "Current Level: 1e100 db"
    for token in user_input.split():
        try:
            # if this succeeds, you have your (first) float
            print float(token), "is a float"
        except ValueError:
            print token, "is something else"
    
    # => Would print ...
    #
    # Current is something else
    # Level: is something else
    # 1e+100 is a float
    # db is something else
    

