Python 正则表达式验证有千位分隔符的数字

1. Mandatory integer and fraction
^[0-9]{1,3}(,[0-9]{3})*\.[0-9]+$

2. Mandatory integer and optional fraction. Decimal dot must be omitted if the fraction is omitted
^[0-9]{1,3}(,[0-9]{3})*(\.[0-9]+)?$

3. Optional integer and optional fraction. Decimal dot must be omitted if the fraction is omitted.
^([0-9]{1,3}(,[0-9]{3})*(\.[0-9]+)?|\.[0-9]+)$

4. The preceding regex, edited to find the number in a larger body of text
\b[0-9]{1,3}(,[0-9]{3])*(\.[0-9]+)?\b|\.[0-9]+\b