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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 _check_cron_env(user,
                    name,
                    value=None):
    '''
    Return the environment changes
    '''
    if value is None:
        value = ""  # Matching value set in salt.modules.cron._render_tab
    lst = __salt__['cron.list_tab'](user)
    for env in lst['env']:
        if name == env['name']:
            if value != env['value']:
                return 'update'
            return 'present'
    return 'absent'