file for parsing .env files in python

dotenv.py

"""
Utility for parsing .env files, as used by docker-compose and a few others.
"""
import re


QUOTED_STRING = r'("(?:(\\.|[^"\\])*)")'
SINGLE_QUOTED_STRING = r"('(?:(\\.|[^'\\])*)')"
VAL = fr'([^\s]+|{QUOTED_STRING}|{SINGLE_QUOTED_STRING})'
LINE = fr'^\s*(?P<key>{VAL})\s*=\s*(?P<val>{VAL})\s*(#.*)?$'


def _strip_quote(val):
  quotes = ('"', "'")
  for quote in quotes:
    if val[0] == quote and val[-1] == quote:
      return val[1:-1].replace("\\", "")
  return val


def parse_lines(lines):
  vals = {}
  for num, line in enumerate(lines):
    if not line.strip():
      continue  # skip blank lines
    match = re.match(LINE, line)
    if not match:
      if line.lstrip()[0] != '#':
        raise ValueError(f'could not parse line {num + 1}: {line}')
      continue
    groups = match.groupdict()
    vals[_strip_quote(groups['key'])] = _strip_quote(groups['val'])
  return vals


def parse_file(path):
  with open(path, encoding="utf-8") as file:
    return parse_lines(file)

dotenv_test.py

from unittest import TestCase
import dotenv


class DotEnvTest(TestCase):
  def test(self):
    assert dotenv.parse_lines([
      'a1 = b1',
      'a2 = b2 # ignore comment',
      ' a3=b3 ',
      'a4="b4\\" "',
      "a5='b5\\' '",
      ' # ...',  # ignore comment only line
      '  ',  # ignore blank line
    ]) == {'a1': 'b1', 'a2': 'b2', 'a3': 'b3', 'a4': 'b4" ', 'a5': "b5' "}

  def test_error(self):
    with self.assertRaises(ValueError):
      dotenv.parse_lines(['invalid line'])