如何从 Python 中的字符串中提取数字？

Question

你如何从字符串中提取一个数字来操作它？该数字可以是 anint或 a float。例如，如果字符串是"flour, 100, grams"or"flour, 100.5, grams"然后提取数字100或100.5.

代码：

string  = "flour, 100, grams"
numbers = [int(x) for x in string.split(",")]
print(numbers)

输出：

Traceback (most recent call last):
  File "/Users/lewis/Documents/extracting numbers.py", line 2, in <module>
    numbers = [int(x) for x in string.split(",")]
 File "/Users/lewis/Documents/extracting numbers.py", line 2, in <listcomp>
   numbers = [int(x) for x in string.split(",")]
ValueError: invalid literal for int() with base 10: 'flour'

Answer 1

给定字符串的结构，当您使用str.split将字符串拆分为三个字符串的列表时，您应该只取三个元素之一：

>>> s = "flour, 100, grams"
>>> s.split(",")
['flour', ' 100', ' grams']
>>> s.split(",")[1] # index the middle element (Python is zero-based)
' 100'

然后，您可以使用float将该字符串转换为数字：

>>> float(s.split(",")[1])
100.0

如果您不能确定字符串的结构，您可以使用re（正则表达式）来提取数字map并将它们全部转换：

>>> import re
>>> map(float, re.findall(r"""\d+ # one or more digits
                              (?: # followed by...
                                  \. # a decimal point 
                                  \d+ # and another set of one or more digits
                              )? # zero or one times""",
                          "Numbers like 1.1, 2, 34 and 15.16.",
                          re.VERBOSE))
[1.1, 2.0, 34.0, 15.16]