90-综合练习：备份程序

1、既要可以实现完全备份，又要实现增量备份
2、完全备份时，将目录打个tar包，计算每个文件的md5值
3、增量备份时，备份有变化的文件和新增加的文件，更新md5值

import time
import os
import tarfile
import hashlib
import pickle

def check_md5(fname):
    m = hashlib.md5()
    with open(fname, 'rb') as fobj:
        while True:
            data = fobj.read(4096)
            if not data:
                break
            m.update(data)
    return m.hexdigest()

def full_backup(src_dir, dst_dir, md5file):
    fname = os.path.basename(src_dir.rstrip('/'))
    fname = '%s_full_%s.tar.gz' % (fname, time.strftime('%Y%m%d'))
    fname = os.path.join(dst_dir, fname)
    md5dict = {}

    tar = tarfile.open(fname, 'w:gz')
    tar.add(src_dir)
    tar.close()

    for path, folders, files in os.walk(src_dir):
        for each_file in files:
            key = os.path.join(path, each_file)
            md5dict[key] = check_md5(key)

    with open(md5file, 'wb') as fobj:
        pickle.dump(md5dict, fobj)


def incr_backup(src_dir, dst_dir, md5file):
    fname = os.path.basename(src_dir.rstrip('/'))
    fname = '%s_incr_%s.tar.gz' % (fname, time.strftime('%Y%m%d'))
    fname = os.path.join(dst_dir, fname)
    md5dict = {}

    with open(md5file, 'rb') as fobj:
        oldmd5 = pickle.load(fobj)

    for path, folders, files in os.walk(src_dir):
        for each_file in files:
            key = os.path.join(path, each_file)
            md5dict[key] = check_md5(key)

    with open(md5file, 'wb') as fobj:
        pickle.dump(md5dict, fobj)

    tar = tarfile.open(fname, 'w:gz')
    for key in md5dict:
        if oldmd5.get(key) != md5dict[key]:
            tar.add(key)
    tar.close()

if __name__ == '__main__':
    # mkdir /tmp/demo; cp -r /etc/security /tmp/demo
    src_dir = '/tmp/demo/security'
    dst_dir = '/var/tmp/backup'   # mkdir /var/tmp/backup
    md5file = '/var/tmp/backup/md5.data'
    if time.strftime('%a') == 'Mon':
        full_backup(src_dir, dst_dir, md5file)
    else:
        incr_backup(src_dir, dst_dir, md5file)