如何从字符串中提取浮点数

Question

我有许多类似的字符串Current Level: 13.4 db.,我想提取浮点数.我说漂浮而不是十进制,因为它有时是完整的.RegEx能做到这一点还是有更好的方法？

Answer 1

如果你的浮点数总是以十进制表示法表示

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

可能就够了.

更强大的版本将是:

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

如果要验证用户输入,也可以通过直接踩到它来检查浮点数:

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

Answer 2

您可能想尝试这样的内容,涵盖所有基础,包括不依赖于数字后面的空格:

>>> 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']
>>>

轻松复制粘贴:

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")

Answer 3

Python文档的答案涵盖+/-和指数表示法

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

此正则表达式不支持国际格式,其中逗号用作整数和小数部分之间的分隔符(3,14159).在这种情况下,更换所有\.与[.,]在上述浮子正则表达式.

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

Answer 4

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

如上所述,效果很好!但有一个建议是:

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

也将返回负的int值(如此字符串末尾的-3)

Answer 5

您可以使用以下正则表达式从字符串中获取整数和浮点值：

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

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

谢谢雷克斯