Validating python regex flags specified in json

Question

I am writing a tool which accepts user configuration via a json file. One piece of this config is a python regular expression and some optional regex flags. Currently the configuration for the regex flags is an array of integers which will all be run through a bitwise or (|) and sent to the re compile method.

My question is how can I validate these integers to ensure that they are valid re flags?

EDIT: Or potentially another solution to my problem... Is it possible for the user to specify the actual re flags in the JSON? I.e., [re.DEBUG, re.IGNORECASE] etc etc and then somehow translate those from the JSON file in my python script?

It seems you may use if option in [2, 4, 8, 16, 32, 64, 128, 256] to validate these. Just note that re.ASCII (256) is only present in Python 3 re. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Sep 10, 2017 at 21:28
@WiktorStribiżew what about my edit? Do you think its possible to allow the user to specify the name of the flag instead? That would be a lot more descriptive and helpful — Ogen
– Ogen, Commented Sep 10, 2017 at 21:32
Then you may create a dictionary and map the names with the real flags, i.e. option_dct = { 're.I' : re.I, etc. } — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Sep 10, 2017 at 21:38

Wiktor Stribiżew · Accepted Answer · 2017-09-11 07:01:06Z

1

You can define a dictionary of all possible flags (they are really few, see re 6.2.2. Module Contents), and just get the value by the corresponding key.

A Python demo:

import re
re_flags = { 're.A' : re.A, 
    're.ASCII' : re.ASCII,
    're.DEBUG' : re.DEBUG,
    're.I' : re.I,
    're.IGNORECASE' : re.IGNORECASE,
    're.L' : re.L,
    're.LOCALE' : re.LOCALE,
    're.M' : re.M,
    're.MULTILINE' : re.MULTILINE,
    're.S' : re.S,
    're.DOTALL' : re.DOTALL,
    're.X' : re.X,
    're.VERBOSE' : re.VERBOSE }
flg = 're.I'                      # User input
if flg in re_flags:               # If the dict contains the key
    print(re_flags[flg])          # Print the value (re.I = 2)

If you still want to go with numbers instead:

import re
print(re.A)           # 256
print(re.ASCII)       # 256
print(re.DEBUG)       # 128
print(re.I)           # 2
print(re.IGNORECASE)  # 2
print(re.L)           # 4
print(re.LOCALE)      # 4
print(re.M)           # 8
print(re.MULTILINE)   # 8
print(re.S)           # 16
print(re.DOTALL)      # 16
print(re.X)           # 64
print(re.VERBOSE)     # 64

edited Sep 11, 2017 at 7:01

answered Sep 11, 2017 at 6:55

Wiktor Stribiżew

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1 Comment

Ogen Over a year ago

Yeah I assigned them to the raw numbers because i don't know whether my script will be being run in python 2 or 3 so if I try to use the re module there are some flags which do not exist in python 2 etc

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