python - How to extract a floating number from a string

Question

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Answer 1

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