Source code for uw.local.deploy.environment

"""Environment-related routines for system deployment.

This includes functions for combining environment settings from various
sources and updating the OS environ accordingly.
"""

import os
import re

env_re = re.compile ('^\s*(?P<var>\w+)\s*=\s*(?P<value>[-.\w]*)\s*$', flags=re.A)

def parse_environment (fp, fname):
    """Parse a file for environment settings.

    :param fp: An iterable of text lines.
    :param fname: The filename, for use in error reporting.
    :return: A dictionary of environment settings parsed from the file.
    """
    result = {}

    for i, line in enumerate (fp, start=1):
        m = env_re.match (line)
        if m is not None:
            result[m.group ('var')] = m.group ('value')
        else:
            raise ValueError ('Unable to parse line %d of environment file "%s"' % (i, fname))

    return result

def combine_environment (*args):
    """Combine environment settings from various sources.

    :param \*args: Sources of environment settings, either a filename to parse
        or a dictionary of predetermined settings.
    :return: A dictionary of the combined settings.

    Combine the given predetermined settings and settings parsed from the
    specified files into a single dictionary.
    """
    result = {}
    for source in args:
        if isinstance (source, dict):
            # Pre-determined environment values
            d = source
        elif isinstance (source, str):
            # Filename to parse
            d = parse_environment (open (source), source)
        else:
            raise TypeError ('combine_environment() args must be dict or str')
        result.update (d)
    return result

def import_environment (*args):
    """Update the OS environ from settings.

    :param \*args: Sources of environment settings, either a filename to parse
        or a dictionary of predetermined settings.

    Use :func:`combine_environment` to combine the sources and update the OS
    environ from the combined settings.
    """
    os.environ.update (combine_environment (*args))