python - Regular expression for letters, dash, underscore, numbers, and space

Question

This is my attempt

def matcher(ex):
    if re.match(r'^[\w|\d][A-Za-z0-9_-]+$', ex):
        print 'yes'

My goal is to match only submission that satisfy all the followings

1. begins with only a letter or a numeric digit, and
2. only letter, space, dash, underscore and numeric digit are allowed
3. all ending spaces are stripped

In my regex, matcher('__') is considered valid. How can I modify to achieve what I want really want? I believe \w also includes underscore. But matcher('_') is not matched...

Answer 1

def matcher(ex):
    ex = ex.rstrip()
    if re.match(r'^[a-zA-Z0-9][ A-Za-z0-9_-]*$', ex):
        print 'yes'

原始正则表达式中的问题：

1. |并不意味着字符类中的交替，而是字面上的管道字符。

2. 您用于+以下字符，表示一个或多个，因此一个字符的字符串'_'不匹配。

3. 你\w在你的第一个字符中使用了，它接受下划线。