Why is an r prefix not always required for regex in Python?

Python regex - r prefix

Some may wonder why the following regex works, even without the r prefix:

<code class="python">import re
print (re.sub('\s+', ' ', 'hello     there      there'))</code>

It is generally thought that the r prefix is required whenever escape sequences are used, but this example seems to contradict that.

Escape sequences and raw strings

The r prefix is used to create a "raw string", which means that the escape sequences in the string will not be interpreted as special characters. This can be useful when you want to use a character that is normally interpreted as an escape sequence, such as the backslash ().

In the example above, the escape sequence s is used to match one or more whitespace characters. Without the r prefix, this escape sequence would be interpreted as a tab character (t). However, because the r prefix is used, the escape sequence is interpreted literally and matches one or more whitespace characters.

Exceptions to the rule

There are a few exceptions to the rule that escape sequences must be used with the r prefix. One exception is the n escape sequence, which is used to represent a newline character. This escape sequence can be used without the r prefix, as shown in the following example:

<code class="python">print '\n'</code>

Another exception is the \ escape sequence, which is used to represent a backslash character. This escape sequence can also be used without the r prefix, as shown in the following example:

<code class="python">print '\'</code>

Conclusion

The r prefix is not always required when using escape sequences in Python. However, it is generally a good idea to use the r prefix to avoid any confusion or unexpected behavior.

The above is the detailed content of Why is an r prefix not always required for regex in Python?. For more information, please follow other related articles on the PHP Chinese website!