I have this regex function to extract a specific word in a string
fileName = re.search(r'path1\w([A-Za-z\d]+)', self.fileList[0]).group(1)
path1 is an actual string
What if I would like to replace it by fileName variable where fileName = "path1"
I tried:
print re.search(r'\w([A-Za-z\d]+)' % fileName, self.fileList[0]).group(1)
I got this error:
TypeError: not all arguments converted during string formatting
Why did I get this error ? how to solve this problem
You need a %s in your regex :
print re.search(r'%s\w([A-Za-z\d]+)' % fileName, self.fileList[0]).group(1)
Or as a more pythoinc and flexible way you can use str.format function :
print re.search(r'{}\w([A-Za-z\d]+)'.format(fileName), self.fileList[0]).group(1)
Note that is second way if you have a list of file names you can loop over them and pass the file names to format.
One should be very careful when interpolating strings into languages like Regex. In this case, you should probably escape the string first:
expression = r'{}\w([A-Za-z\d]+)'.format(re.escape(fileName))
re.search(expression, self.fileList[0]).group(1)
It's maybe also worth noting regex's named lists:
import regex
expression = regex.compile(r'\L<filename>\w([A-Za-z\d]+)', filename=[fileName])
expression.search(self.fileList[0]).group(1)
This avoids having to regex-escape the literal, and works better if there are multiple options. (Plus regex is tons better anyway, so all the more reason to use it!)
