本文实例讲述了Python多进程分块读取超大文件的方法。分享给大家供大家参考，具体如下：
读取超大的文本文件，使用多进程分块读取，将每一块单独输出成文件
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# -*- coding: GBK -*-import urlparseimport datetimeimport osfrom multiprocessing import Process,Queue,Array,RLock"""多进程分块读取文件"""WORKERS = 4BLOCKSIZE = 100000000FILE_SIZE = 0def getFilesize(file): """ 获取要读取文件的大小 """ global FILE_SIZE fstream = open(file,'r') fstream.seek(0,os.SEEK_END) FILE_SIZE = fstream.tell() fstream.close()def process_found(pid,array,file,rlock): global FILE_SIZE global JOB global PREFIX """ 进程处理 Args: pid:进程编号 array:进程间共享队列，用于标记各进程所读的文件块结束位置 file:所读文件名称 各个进程先从array中获取当前最大的值为起始位置startpossition 结束的位置endpossition (startpossition+BLOCKSIZE) if (startpossition+BLOCKSIZE)<FILE_SIZE else FILE_SIZE if startpossition==FILE_SIZE则进程结束 if startpossition==0则从0开始读取 if startpossition!=0为防止行被block截断的情况，先读一行不处理，从下一行开始正式处理 if 当前位置 <=endpossition 就readline 否则越过边界，就从新查找array中的最大值 """ fstream = open(file,'r') while True: rlock.acquire() print 'pid%s'%pid,','.join([str(v) for v in array]) startpossition = max(array) endpossition = array[pid] = (startpossition+BLOCKSIZE) if (startpossition+BLOCKSIZE)<FILE_SIZE else FILE_SIZE rlock.release() if startpossition == FILE_SIZE:#end of the file print 'pid%s end'%(pid) break elif startpossition !=0: fstream.seek(startpossition) fstream.readline() pos = ss = fstream.tell() ostream = open('/data/download/tmp_pid'+str(pid)+'_jobs'+str(endpossition),'w') while pos<endpossition: #处理line line = fstream.readline() ostream.write(line) pos = fstream.tell() print 'pid:%s,startposition:%s,endposition:%s,pos:%s'%(pid,ss,pos,pos) ostream.flush() ostream.close() ee = fstream.tell() fstream.close()def main(): global FILE_SIZE print datetime.datetime.now().strftime("%Y/%d/%m %H:%M:%S") file = "/data/pds/download/scmcc_log/tmp_format_2011004.log" getFilesize(file) print FILE_SIZE rlock = RLock() array = Array('l',WORKERS,lock=rlock) threads=[] for i in range(WORKERS): p=Process(target=process_found, args=[i,array,file,rlock]) threads.append(p) for i in range(WORKERS): threads[i].start() for i in range(WORKERS): threads[i].join() print datetime.datetime.now().strftime("%Y/%d/%m %H:%M:%S") if __name__ == '__main__': main() |
希望本文所述对大家Python程序设计有所帮助。
