教你用100多行写一个数据库

本文介绍的是以为中国的IT资深人士写的一个简单的数据库，没有我们使用的数据库那么强大，但是值得大家借鉴。可以用在特定环境中，更加灵活方便。

100多行的数据库代码

# -*- coding:utf-8 -*-
import os
import time
import bisect
import itertools
from datetime import datetime
import logging
  
default_data_dir = './data/'
default_write_buffer_size = 1024*10
default_read_buffer_size = 1024*10
default_index_interval = 1000
  
def ensure_data_dir():
    if not os.path.exists(default_data_dir):
        os.makedirs(default_data_dir)
  
def init():
    ensure_data_dir()
  
class WawaIndex:
    def __init__(self, index_name):
        self.fp_index = open(os.path.join(default_data_dir, index_name + '.index'), 'a+', 1)
        self.indexes, self.offsets, self.index_count = [], [], 0
        self.__load_index()
  
    def __update_index(self, key, offset):
        self.indexes.append(key)
        self.offsets.append(offset)
  
    def __load_index(self):
        self.fp_index.seek(0)
        for line in self.fp_index:
            try:
                key, offset  = line.split()
                self.__update_index(key, offset)
            except ValueError: # 索引如果没有flush的话，可能读到有半行的数据
                pass
  
    def append_index(self, key, offset):
        self.index_count += 1
        if self.index_count % default_index_interval == 0:
            self.__update_index(key, offset)
            self.fp_index.write('%s %s %s' % (key, offset, os.linesep))
  
    def get_offsets(self, begin_key, end_key):
        left = bisect.bisect_left(self.indexes, str(begin_key))
        right = bisect.bisect_left(self.indexes, str(end_key))
        left, right = left - 1, right - 1
        if left   len(self.indexes) - 1: right = len(self.indexes) - 1
        logging.debug('get_index_range:%s %s %s %s %s %s', self.indexes[0], self.indexes[-1], begin_key, end_key, left, right)
        return self.offsets[left], self.offsets[right]
  
  
class WawaDB:
    def __init__(self, db_name):
        self.db_name = db_name
        self.fp_data_for_append = open(os.path.join(default_data_dir, db_name + '.db'), 'a', default_write_buffer_size)
        self.index = WawaIndex(db_name)
  
    def __get_data_by_offsets(self, begin_key, end_key, begin_offset, end_offset):
        fp_data = open(os.path.join(default_data_dir, self.db_name + '.db'), 'r', default_read_buffer_size)
        fp_data.seek(int(begin_offset))
          
        line = fp_data.readline()
        find_real_begin_offset = False
        will_read_len, read_len = int(end_offset) - int(begin_offset), 0
        while line:
            read_len += len(line)
            if (not find_real_begin_offset) and  (line  = will_read_len) and (line > str(end_key)): break
            yield line.rstrip('\r\n')
            line = fp_data.readline()
  
    def append_data(self, data, record_time=datetime.now()):
        def check_args():
            if not data:
                raise ValueError('data is null')
            if not isinstance(data, basestring):
                raise ValueError('data is not string')
            if data.find('\r') != -1 or data.find('\n') != -1:
                raise ValueError('data contains linesep')
  
        check_args()
          
        record_time = time.mktime(record_time.timetuple())
        data = '%s %s %s' % (record_time, data, os.linesep)
        offset = self.fp_data_for_append.tell()
        self.fp_data_for_append.write(data)
        self.index.append_index(record_time, offset)
  
    def get_data(self, begin_time, end_time, data_filter=None):
        def check_args():
            if not (isinstance(begin_time, datetime) and isinstance(end_time, datetime)):
                raise ValueError('begin_time or end_time is not datetime')
  
        check_args()
  
        begin_time, end_time = time.mktime(begin_time.timetuple()), time.mktime(end_time.timetuple())
        begin_offset, end_offset = self.index.get_offsets(begin_time, end_time)
  
        for data in self.__get_data_by_offsets(begin_time, end_time, begin_offset, end_offset):
            if data_filter:
                if data_filter(data):
                    yield data
            else:
                yield data
  
def test():
    from datetime import datetime, timedelta
    import uuid, random
    logging.getLogger().setLevel(logging.NOTSET)
  
    def time_test(test_name):
        def inner(f):
            def inner2(*args, **kargs):
                start_time = datetime.now()
                result = f(*args, **kargs)
                print '%s take time:%s' % (test_name, (datetime.now() - start_time))
                return result
            return inner2
        return inner
  
    @time_test('gen_test_data')   
    def gen_test_data(db):
        now = datetime.now()
        begin_time = now - timedelta(hours=5)
        while begin_time  

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