Ndtyjky

I am building a regex checking tool using python, where the user creates the pattern, checks the flags he/she needs, and then tests different strings using the generated pattern. Python has 6 regex flags: re.I, re.M, re.S, re.U, re.L, and re.X, so writing an if-else statement would be a nightmare, thanks to all the combinations.

Is there a way to define the flags as just boolean values instead? Something like this:

re.compile(pattern, re.IGNORECASE=ignorecase, re.MULTILINE=multiline, ...)

The above code does not work, but hopefully it makes it clear. The pattern, ignorecase, and multiline are all variables defined by the user using a simple form containing an input for the patter, and checkboxes for the flags.

Any help is appreciated.

What you need is a convenient way to combine enabled flags into a single argument that you can pass. Instead of setting a different value for each flag, I would advise simply checking what is set (in whatever way you already do this), and immediately merging the corresponding flag into a single accumulator variable.

For example, supposing the flags were specified as command line arguments I might do it like this:

userchoices = 0

if "-a in opts:

    userchoices |= re.A

if "-i" in opts:

    userchoices |= re.I

if "-L" in opts:

    userchoices |= re.L

etc.



matcher = re.compile(pattern, flags=userchoices)

If you have already written the code that initializes each of your named variables to the corresponding re.? constant, you can simply collect them into an array and OR them together like this:

from operator import or_

from functools import reduce

userchoices = reduce(or_, [asciionly, ignorecase, multiline, ...])

Depending on how you detect the user's selections, you could streamline this further by e.g. using a dictionary to map the options of your form to python constants, etc.

PS. An alternative approach: each flag can be expressed by the corresponding letter and embedded in the regexp itself. So you could do something like this, and bypass the flags argument altogether:

userflags = "".join([asciionly, ignorecase, multiline, ...])

matcher = re.compile("(?%s)%s" % (userflags, pattern) )

I think this is kind of hacky, to be honest, but there may be a place for it since the regexp encapsulates the settings it is being used with.