code: def parse_env_var(s):
      
      parts = s.split('=', 1)
      if len(parts) == 2:
          k, v = parts
          return (k, v)
  
      k = parts[0]
      return (k, os.getenv(k, ''))
docs: Parse an environment variable string
  
      Returns a key-value tuple
  
      Apply the same logic as `docker run -e`:
      "If the operator names an environment variable without specifying a value,
      then the current value of the named variable is propagated into the
      container's environment