blocks|key|2941989|text|你快到了！在regex中，*匹配给定字符的零或多个，总是匹配最长的序列。例如，A*将与AAAbcde匹配，匹配将是AAA。它还将与BCDE匹配空匹配，但仍然匹配。为了实现您想要的结果，您需要在模式的末尾添加$：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2941990|re.match("[a-zA-Z_][0-9a-zA-Z_]*$",name)|code-block|syntax|javascript|2941991|这要求模式与输入匹配，直到行尾，由$表示。|2941992|如果使用的是re.search，则需要使用%5E启动模式。但是，对于re.match，它不是必需的，因为它只匹配字符串的开头：Python3文档:搜索与匹配。|2941993|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.python.org/3/library/re.html#search-vs-match^0|D|1|13|2|17|7|1L|3|1T|4|2V|1|0|0|H|1|0|6|9|L|1|W|8|1P|F|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|19|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1A|8|@$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|1D|8|@$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]]|D|@$9|1K|A|1L|1|1M]]|E|$]]|$1|O|3|-4|5|6|7|1N|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

You are almost there! In regex, the <code>*</code> matches zero or more of the given character, always matching the longest sequence. For instance <code>A*</code> will match with <code>AAAbcde</code> and the match will be <code>AAA</code>. It would also match with <code>BCDE</code> wit an empty match, but a match nonetheless. To achieve what you want you need to add <code>$</code> at the end of your pattern:

<pre><code>re.match("[a-zA-Z_][0-9a-zA-Z_]*$",name)
</code></pre>

This requests for the pattern to match the input until the end of the line, represented by <code>$</code>

If you were using <code>re.search</code>, you would need to start the pattern with <code>^</code>. However it is not necessary with <code>re.match</code> since it only matches from the beginning of the string: <a href="https://docs.python.org/3/library/re.html#search-vs-match" rel="nofollow noreferrer">Python3 doc: search vs match</a>

blocks|key|1611979|text|您想要匹配完整的字符串才能成功。[a-zA-Z_][0-9a-zA-Z_]*与qq-q匹配，因为您应该在这里检查边界。看看例1，看看匹配的组是什么。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1611980|您可以添加类似于例2的边界。|1611981|entityMap|0|LINK|mutability|MUTABLE|url|https://regex101.com/r/RgVEVZ/2|1|https://regex101.com/r/RgVEVZ/1^0|G|M|13|4|1P|2|0|0|8|2|1|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@$9|W|A|X|1|Y]]|E|$]]|$1|F|3|G|5|6|7|Z|8|@]|D|@$9|10|A|11|1|12]]|E|$]]|$1|H|3|-4|5|6|7|13|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]|P|$5|K|L|M|E|$N|Q]]]]

You want to match the complete string to succeed. <code>[a-zA-Z_][0-9a-zA-Z_]*</code> matches <code>qq-q</code> because you should check for boundaries here. Look at <a href="https://regex101.com/r/RgVEVZ/2" rel="nofollow noreferrer">example 1</a> to see what the matching groups are. 

You can add boundaries like in <a href="https://regex101.com/r/RgVEVZ/1" rel="nofollow noreferrer">example 2</a>.

blocks|key|2904337|text|到大部分完整的字符串"[A-Za-z][A-Za-z\d_]*$",+name)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2904338|没有输出名称=‘qq’和名称='kri[shna0‘|2904339|编辑以匹配下划线|2904340|参见此链接|2904341|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/3361449/regex-to-check-the-string-contains-only-letter-and-numbers-but-not-only-numbers^0|A|U|0|0|0|3|2|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|X|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|Y|8|@]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|L|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|M|$N|$5|O|P|Q|E|$R|S]]]]

To much the complete string <code>"[A-Za-z][A-Za-z\d_]*$", name)</code>

no output for name='qq-q' and for name ='kri[shna0'

Edited to match underscore

see this <a href="https://stackoverflow.com/questions/3361449/regex-to-check-the-string-contains-only-letter-and-numbers-but-not-only-numbers">link</a>

blocks|key|1612022|text|你不知道为什么你认为它符合“-”和“[”？这是正确的行为。re.match基本上是查找在字符串开头指定的正则表达式。在这种情况下，它将是kri和qq，因为下一个字符不在您的正则表达式中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1612023|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Not sure why you think it matches '-' and '['?
This is the correct behavior. re.match basically looks for the regex you specified at beginning of the string. In this case it would be kri and qq because the next char is not in your regex.

blocks|key|2904403|text|如果您对regexen有问题，可以始终使用普通python方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2904404|>>>+import+string
>>>+string.ascii_letters
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
>>>+string.ascii_letters+%2B+string.digits+%2B+'_'
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_'
>>>+allowed+=+set(string.ascii_letters+%2B+string.digits+%2B+'_')
>>>+allowed
{'X',+'s',+'f',+'C',+'L',+'V',+'D',+'0',+'H',+'N',+'9',+'l',+'c',+'b',+'p',+'n',+'W',+'k',+'O',+'q',+'a',+'Q',+'J',+'r',+'3',+'g',+'h',+'P',+'8',+'T',+'2',+'u',+'w',+'5',+'R',+'Z',+'Y',+'m',+'e',+'_',+'1',+'j',+'t',+'S',+'v',+'G',+'o',+'d',+'A',+'B',+'F',+'M',+'y',+'z',+'E',+'7',+'x',+'I',+'6',+'K',+'U',+'i',+'4'}
>>>+name+=+'qq-q'
>>>+not+name[0].isdigit()+and+all(char+in+allowed+for+char+in+name)
False
>>>+name+=+'Aaf0fg5f0g0e'
>>>+not+name[0].isdigit()+and+all(char+in+allowed+for+char+in+name)
True|code-block|syntax|javascript|2904405|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If you have troubles with regexen, you can always use plain python methods :

<pre><code>&gt;&gt;&gt; import string
&gt;&gt;&gt; string.ascii_letters
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
&gt;&gt;&gt; string.ascii_letters + string.digits + '_'
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_'
&gt;&gt;&gt; allowed = set(string.ascii_letters + string.digits + '_')
&gt;&gt;&gt; allowed
{'X', 's', 'f', 'C', 'L', 'V', 'D', '0', 'H', 'N', '9', 'l', 'c', 'b', 'p', 'n', 'W', 'k', 'O', 'q', 'a', 'Q', 'J', 'r', '3', 'g', 'h', 'P', '8', 'T', '2', 'u', 'w', '5', 'R', 'Z', 'Y', 'm', 'e', '_', '1', 'j', 't', 'S', 'v', 'G', 'o', 'd', 'A', 'B', 'F', 'M', 'y', 'z', 'E', '7', 'x', 'I', '6', 'K', 'U', 'i', '4'}
&gt;&gt;&gt; name = 'qq-q'
&gt;&gt;&gt; not name[0].isdigit() and all(char in allowed for char in name)
False
&gt;&gt;&gt; name = 'Aaf0fg5f0g0e'
&gt;&gt;&gt; not name[0].isdigit() and all(char in allowed for char in name)
True
</code></pre>

I want to use regular expression('re') to find if variable names consist only of Latin letters, digits and underscores and they can't start with a digit.

I tried using 

<pre><code>In [3]: name='qq-q'

In [4]: re.match("[a-zA-Z_][0-9a-zA-Z_]*",name)
Out[4]: &lt;_sre.SRE_Match object; span=(0, 2), match='qq'&gt;

In [5]: name='kri[shna0'

In [6]: re.match("[a-zA-Z_][0-9a-zA-Z_]*",name)
Out[6]: &lt;_sre.SRE_Match object; span=(0, 3), match='kri'&gt;
</code></pre>

Can some one explain me why above expression matches '-' and '[' in above?

use RE to find string consisting only of Latin letters, digits and underscores and they can't start with a digit

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我想使用正则表达式(‘re’)来查找变量名是否仅由拉丁字母、数字和下划线组成，并且它们不能以数字开头。我试着用In [3]: name='qq-q'In [4]: re.match("[a-zA-Z_][0-9a-zA-Z_]*",name)Out[4]: <_sre.SRE_Match object; span=(0, 2), match='qq'>In [5]: name='kri[shna0

问使用RE查找仅由拉丁字母、数字和下划线组成的字符串，它们不能以数字开头
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回答 5

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