Generate random string from regex character set
python, regex, string
Solution
Paul McGuire, author of Pyparsing, has written an inverse regex parser, with which you could do this:
import invRegex
print(''.join(invRegex.invert('[a-z]')))
# abcdefghijklmnopqrstuvwxyz
If you do not want to install Pyparsing, there is also a regex inverter that uses only modules from the standard library with which you could write:
import inverse_regex
print(''.join(inverse_regex.ipermute('[a-z]')))
# abcdefghijklmnopqrstuvwxyz
Note: neither module can invert all regex patterns.
And there are differences between the two modules:
import invRegex
import inverse_regex
print(repr(''.join(invRegex.invert('.'))))
print(repr(''.join(inverse_regex.ipermute('.'))))
yields
'0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~'
'0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~ \t\n\r\x0b\x0c'
Here is another difference, this time pyparsing enumerates a larger set of matches:
x = list(invRegex.invert('[a-z][0-9]?.'))
y = list(inverse_regex.ipermute('[a-z][0-9]?.'))
print(len(x))
# 26884
print(len(y))
# 1100
Problem
I assume there's some beautiful Pythonic way to do this, but I haven't quite figured it out yet. Basically I'm looking to create a testing module and would like a nice simple way for users to define a character set to pull from. I could potentially concatenate a list of the various charsets associated with string, but that strikes me as a very unclean solution. Is there any way to get the charset that the regex represents? Example: ``` def foo(regex_set): re.something(re.compile(regex_set)) foo("[a-z]") >>> abcdefghijklmnopqrstuvwxyz ``` The compile is of course optional, but in my mind that's what this function would look like.