在re.findall（）正则表达式函数中使用变量

Question

I have a list of regex patterns like k[az]p[az]+a and a list of words that can fit into these patterns. Now, the problem is that, when I use:

re.findall(r'k[a-z]p[a-z]+a', list)

Everything works properly, but when I replace the raw expression with a variable like:

pattern = "r'" + pattern + "'"

and then try:

re.findall(pattern, list)

or

re.findall(str(pattern), list)

It no longer works. How could I fix it?

Thanks! Spike

Answer 1

You are overthinking it. The r prefix is not part of the pattern string itself, it merely indicates that the following string should not use escape codes for certain characters.

This will work without adjusting your pattern:

re.findall(pattern, list)

If your pattern contains characters that do not need escaping (as they do not), you can add the prefix r to the pattern definition. Suppose you want to search for a different regex, then use

pattern = r'k\wp\wa'
re.findall(pattern, list)

and you don't need to escape it. Since pattern in itself is a perfectly ordinary string, you can concatenate it with other strings:

start = 'a'
middle = 'b'
end = 'c'
pattern = a + r'\w' + b + r'\w' + c
re.findall(pattern, list)