正则表达式不允许在字符串中间出现两个连续的空格 [英] Regular Expression to disallow two consecutive white spaces in the middle of a string

问题描述

我需要一个正则表达式来满足以下要求:

I need a regex to meet the following requirements:

• 仅允许使用字母，句点和空格.
• 字符串的开头和结尾没有空格.
• 字符串中间的空格可以，但是不能连续两个空格.

比赛:

"Hello world."
"Hello World. This is ok."

不匹配:

" Hello World. "
"Hello world 123." 
"Hello  world."

在我看来，这是可行的

<asp:RegularExpressionValidator ID="revDescription" runat="server" 
                                ControlToValidate="taDescription" Display="Dynamic" ErrorMessage="Invalid Description." 
                                Text="&nbsp" 
                                ValidationExpression="^(?i)(?![ ])(?!.*[ ]{2})(?!.*[ ]$)[A-Z. ]{8,20}$"></asp:RegularExpressionValidator>

推荐答案

这是Python中的解决方案，使用锚和否定超前断言，以确保遵循空白规则:

Here's a solution in Python, using anchors and negative lookahead assertions to make sure the whitespace rules are followed:

regex = re.compile(
    """^          # Start of string
    (?![ ])       # Assert no space at the start
    (?!.*[ ]{2})  # Assert no two spaces in the middle
    (?!.*[ ]$)    # Assert no space at the end
    [A-Z. ]{8,20} # Match 8-20 ASCII letters, dots or spaces
    $             # End of string""", 
    re.IGNORECASE | re.VERBOSE)

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