Flowpoke Flowpoke - 1 year ago 78
Python Question

How to extract a floating number from a string in Python

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 Source

If your float is always expressed in decimal notation something like

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

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():
        # 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
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