Regex to match less than 500 feet with decimal places in a string

Question

I am trying to use regular expressions to determine if a string contains a value of less than 500 feet. Importantly, there are some key constraints and assumptions to the matching:

• Can assume commas have been stripped. Decimals are guaranteed to be . and not ,
• Cannot assume the numeric value is preceded by a space.
• Can assume "feet" will be written as "ft" or "feet"
• Can assume lowercase
• Decimals can be any length
• There may be any number of spaces between the number and word "feet" or "ft"

My attempts thus far:

Attempt 1

\b[1-4]{0,1}[0-9]{1,2}(\.[0-9]{1,}}){0,1} {0,}(ft|feet)\b

This was good, but failed to account for decimals and matches values like 1000.5 ft (matching "5 ft")

Attempt 2

My next attempt was to include a negative lookbehind to make sure the match wasn't preceded by a . or any number.

(?<!(\.|[0-9]))([1-4]{0,1}[0-9]{1,2}(\.[0-9]{1,}}){0,1} {0,}(ft|feet))\b

Unfortunately, this doesn't match any decimals now (e.g., 5.5 ft should match but doesn't). I suspect I'm misunderstanding how negative lookbehind works.

I would appreciate any help understanding where I'm going wrong!

Test Cases:

• "1 ft tall" - match
• "1ft tall" - match
• "1.1ft tall" - match
• "He is 6 feet tall" - match
• "499.555 feet tall" - match
• "He is 2 m tall" - no match
• "500 feet tall" - no match
• "The building is 1000.405 ft tall" - no match

Answer 1

您可以使用

r"(?<!\d\.)(?<!\d)(?:[1-9]|[1-9]\d|[1-4]\d\d)(?:\.\d+)?\s*f(?:ee)?t\b"

请参见regex demo

详细信息

• (?<!\d\.)(?<!\d)-两个否定的隐含含义，以确保当前位置之前没有数字+点或仅一个数字
• (?:[1-9]|[1-9]\d|[1-4]\d\d)-一个数字
  • [1-9]-从1到9
  • [1-9]\d-从10到99
  • [1-4]\d\d-100至499
• (?:\.\d+)?-一个可选的非捕获组，匹配点的可选顺序，然后是1个以上的数字
• \s*-超过0个空格
• f(?:ee)?t-ft或feet（但不是fet）
• \b-单词边界。