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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_default_version(env):
 """Returns the default version string to use for MSVS. If no version was requested by the user through the MSVS environment variable, query all the available visual studios through get_installed_visual_studios, and take the highest one. Return ------ version: str the default version. """

    if 'MSVS' not in env or not SCons.Util.is_Dict(env['MSVS']):
        # get all versions, and remember them for speed later
        versions = [vs.version for vs in get_installed_visual_studios()]
        env['MSVS'] = {'VERSIONS' : versions}
    else:
        versions = env['MSVS'].get('VERSIONS', [])

    if 'MSVS_VERSION' not in env:
        if versions:
            env['MSVS_VERSION'] = versions[0] #use highest version by default
        else:
            debug('get_default_version: WARNING: no installed versions found, '
                  'using first in SupportedVSList (%s)'%SupportedVSList[0].version)
            env['MSVS_VERSION'] = SupportedVSList[0].version

    env['MSVS']['VERSION'] = env['MSVS_VERSION']

    return env['MSVS_VERSION']