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How to extract a floating number from a string [duplicate]

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How do you extract a floating number from a string in Python?

To extract a floating number from a string with Python, we call the re. findall method. import re d = re. findall("\d+\.

How do I extract a decimal from a string in Python?

Using RegEx module is the fastest way.

How do you convert a string to a float?

We can convert a string to float in Python using the float() function. This is a built-in function used to convert an object to a floating point number. Internally, the float() function calls specified object __float__() function.


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

You may like to try something like this which covers all the bases, including not relying on whitespace after the number:

>>> import re
>>> numeric_const_pattern = r"""
...     [-+]? # optional sign
...     (?:
...         (?: \d* \. \d+ ) # .1 .12 .123 etc 9.1 etc 98.1 etc
...         |
...         (?: \d+ \.? ) # 1. 12. 123. etc 1 12 123 etc
...     )
...     # followed by optional exponent part if desired
...     (?: [Ee] [+-]? \d+ ) ?
...     """
>>> rx = re.compile(numeric_const_pattern, re.VERBOSE)
>>> rx.findall(".1 .12 9.1 98.1 1. 12. 1 12")
['.1', '.12', '9.1', '98.1', '1.', '12.', '1', '12']
>>> rx.findall("-1 +1 2e9 +2E+09 -2e-9")
['-1', '+1', '2e9', '+2E+09', '-2e-9']
>>> rx.findall("current level: -2.03e+99db")
['-2.03e+99']
>>>

For easy copy-pasting:

numeric_const_pattern = '[-+]? (?: (?: \d* \. \d+ ) | (?: \d+ \.? ) )(?: [Ee] [+-]? \d+ ) ?'
rx = re.compile(numeric_const_pattern, re.VERBOSE)
rx.findall("Some example: Jr. it. was .23 between 2.3 and 42.31 seconds")

Python docs has an answer that covers +/-, and exponent notation

scanf() Token      Regular Expression
%e, %E, %f, %g     [-+]?(\d+(\.\d*)?|\.\d+)([eE][-+]?\d+)?
%i                 [-+]?(0[xX][\dA-Fa-f]+|0[0-7]*|\d+)

This regular expression does not support international formats where a comma is used as the separator character between the whole and fractional part (3,14159). In that case, replace all \. with [.,] in the above float regex.

                        Regular Expression
International float     [-+]?(\d+([.,]\d*)?|[.,]\d+)([eE][-+]?\d+)?

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

as described above, works really well! One suggestion though:

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

will also return negative int values (like -3 in the end of this string)


You can use the following regex to get integer and floating values from a string:

re.findall(r'[\d\.\d]+', 'hello -34 42 +34.478m 88 cricket -44.3')

['34', '42', '34.478', '88', '44.3']

Thanks Rex