如何在python中拆分一个巨大的文本文件

linux有一个split命令

退房 os.stat() file.readlines([sizehint])

作为替代方法,使用日志库:

>>> import logging.handlers
>>> log = logging.getLogger()
>>> fh = logging.handlers.RotatingFileHandler("D://filename.txt", 
     maxBytes=2**20*100, backupCount=100) 
# 100 MB each, up to a maximum of 100 files
>>> log.addHandler(fh)
>>> log.setLevel(logging.INFO)
>>> f = open("D://biglog.txt")
>>> while True:
...     log.info(f.readline().strip())

您的文件将显示如下:

filename.txt(文件末尾)
filename.txt.1
filename.txt.2

filename.txt.10(文件开头)

这是一种快速简便的方法,可以使一个巨大的日志文件与您的 RotatingFileHandler 实施

https://pypi.org/project/filesplit/

别忘了 seek() 和 mmap() 用于随机访问文件。

def getSomeChunk(filename, start, len):
    fobj = open(filename, 'r+b')
    m = mmap.mmap(fobj.fileno(), 0)
    return m[start:start+len]

这种生成器方法是一种(缓慢的)方式,可以在不破坏内存的情况下获得一段线。

import itertools

def slicefile(filename, start, end):
    lines = open(filename)
    return itertools.islice(lines, start, end)

out = open("/blah.txt", "w")
for line in slicefile("/python27/readme.txt", 10, 15):
    out.write(line)

虽然 Ryan Ginstrom's answer itertools.islice 通过依次迭代打开的文件描述符:

def splitfile(infilepath, chunksize):
    fname, ext = infilepath.rsplit('.',1)
    i = 0
    written = False
    with open(infilepath) as infile:
        while True:
            outfilepath = "{}{}.{}".format(fname, i, ext)
            with open(outfilepath, 'w') as outfile:
                for line in (infile.readline() for _ in range(chunksize)):
                    outfile.write(line)
                written = bool(line)
            if not written:
                break
            i += 1

你可以用 wc 和 split bash :

split -dl$((`wc -l 'filename'|sed 's/ .*$//'` / 3 + 1)) filename filename-chunk.

生成相同行数的3个部分(当然最后一个部分有舍入错误),命名为 filename-chunk.00 到 filename-chunk.02 .

我已经写了这个程序,看起来效果不错。谢谢卡米尔·基希尔让我开始学习。
(请注意,FileSizeParts()是此处未显示的函数)
稍后我可能会花时间做一个二进制读取的版本,看看它是否更快。

def Split(inputFile,numParts,outputName):
    fileSize=os.stat(inputFile).st_size
    parts=FileSizeParts(fileSize,numParts)
    openInputFile = open(inputFile, 'r')
    outPart=1
    for part in parts:
        if openInputFile.tell()<fileSize:
            fullOutputName=outputName+os.extsep+str(outPart)
            outPart+=1
            openOutputFile=open(fullOutputName,'w')
            openOutputFile.writelines(openInputFile.readlines(part))
            openOutputFile.close()
    openInputFile.close()
    return outPart-1

用法-split.py文件名splitsizeinkb

import os
import sys

def getfilesize(filename):
   with open(filename,"rb") as fr:
       fr.seek(0,2) # move to end of the file
       size=fr.tell()
       print("getfilesize: size: %s" % size)
       return fr.tell()

def splitfile(filename, splitsize):
   # Open original file in read only mode
   if not os.path.isfile(filename):
       print("No such file as: \"%s\"" % filename)
       return

   filesize=getfilesize(filename)
   with open(filename,"rb") as fr:
    counter=1
    orginalfilename = filename.split(".")
    readlimit = 5000 #read 5kb at a time
    n_splits = filesize//splitsize
    print("splitfile: No of splits required: %s" % str(n_splits))
    for i in range(n_splits+1):
        chunks_count = int(splitsize)//int(readlimit)
        data_5kb = fr.read(readlimit) # read
        # Create split files
        print("chunks_count: %d" % chunks_count)
        with open(orginalfilename[0]+"_{id}.".format(id=str(counter))+orginalfilename[1],"ab") as fw:
            fw.seek(0) 
            fw.truncate()# truncate original if present
            while data_5kb:                
                fw.write(data_5kb)
                if chunks_count:
                    chunks_count-=1
                    data_5kb = fr.read(readlimit)
                else: break            
        counter+=1 

if __name__ == "__main__":
   if len(sys.argv) < 3: print("Filename or splitsize not provided: Usage:     filesplit.py filename splitsizeinkb ")
   else:
       filesize = int(sys.argv[2]) * 1000 #make into kb
       filename = sys.argv[1]
       splitfile(filename, filesize)

下面是一个python脚本,可用于使用 subprocess :

"""
Splits the file into the same directory and
deletes the original file
"""

import subprocess
import sys
import os

SPLIT_FILE_CHUNK_SIZE = '5000'
SPLIT_PREFIX_LENGTH = '2'  # subprocess expects a string, i.e. 2 = aa, ab, ac etc..

if __name__ == "__main__":

    file_path = sys.argv[1]
    # i.e. split -a 2 -l 5000 t/some_file.txt ~/tmp/t/
    subprocess.call(["split", "-a", SPLIT_PREFIX_LENGTH, "-l", SPLIT_FILE_CHUNK_SIZE, file_path,
                     os.path.dirname(file_path) + '/'])

    # Remove the original file once done splitting
    try:
        os.remove(file_path)
    except OSError:
        pass

您可以在外部称之为:

import os
fs_result = os.system("python file_splitter.py {}".format(local_file_path))

子流程 创建一个内存占用与进程大小相同的fork,如果进程内存已经很重,则在运行时将其加倍。同样的事情 os.system .

下面是另一种纯python的方法,虽然我没有在大型文件上测试过,但速度会慢一些,但内存会更精简:

CHUNK_SIZE = 5000

def yield_csv_rows(reader, chunk_size):
    """
    Opens file to ingest, reads each line to return list of rows
    Expects the header is already removed
    Replacement for ingest_csv
    :param reader: dictReader
    :param chunk_size: int, chunk size
    """
    chunk = []
    for i, row in enumerate(reader):
        if i % chunk_size == 0 and i > 0:
            yield chunk
            del chunk[:]
        chunk.append(row)
    yield chunk

with open(local_file_path, 'rb') as f:
    f.readline().strip().replace('"', '')
    reader = unicodecsv.DictReader(f, fieldnames=header.split(','), delimiter=',', quotechar='"')
    chunks = yield_csv_rows(reader, CHUNK_SIZE)
    for chunk in chunks:
        if not chunk:
            break
        # Do something with your chunk here

readlines() :

"""
Simple example using readlines()
where the 'file' is generated via:
seq 10000 > file
"""
CHUNK_SIZE = 5


def yield_rows(reader, chunk_size):
    """
    Yield row chunks
    """
    chunk = []
    for i, row in enumerate(reader):
        if i % chunk_size == 0 and i > 0:
            yield chunk
            del chunk[:]
        chunk.append(row)
    yield chunk


def batch_operation(data):
    for item in data:
        print(item)


with open('file', 'r') as f:
    chunks = yield_rows(f.readlines(), CHUNK_SIZE)
    for _chunk in chunks:
        batch_operation(_chunk)

readlines示例演示如何对数据进行分块,以便将分块传递给需要分块的函数。不幸的是,readlines在内存中打开了整个文件,为了提高性能,最好使用reader示例。虽然如果您可以轻松地将所需内容放入内存,并需要分块处理,这就足够了。

import os

fil = "inputfile"
outfil = "outputfile"

f = open(fil,'r')

numbits = 1000000000

for i in range(0,os.stat(fil).st_size/numbits+1):
    o = open(outfil+str(i),'w')
    segment = f.readlines(numbits)
    for c in range(0,len(segment)):
        o.write(segment[c]+"\n")
    o.close()

您可以实现将任何文件拆分为块,如下所示,块大小为500000字节(500kb),内容可以是任何文件:

for idx,val in enumerate(get_chunk(content, CHUNK_SIZE)):
    data=val
    index=idx

def get_chunk(content,size):
        for i in range(0,len(content),size):
            yield content[i:i+size]

我需要拆分csv文件以导入Dynamics CRM,因为导入的文件大小限制为8MB,并且我们收到的文件要大得多。此程序允许用户输入文件名和LinesPerFile,然后将指定的文件拆分为请求的行数。我真不敢相信它的速度有多快!

# user input FileNames and LinesPerFile
FileCount = 1
FileNames = []
while True:
    FileName = raw_input('File Name ' + str(FileCount) + ' (enter "Done" after last File):')
    FileCount = FileCount + 1
    if FileName == 'Done':
        break
    else:
        FileNames.append(FileName)
LinesPerFile = raw_input('Lines Per File:')
LinesPerFile = int(LinesPerFile)

for FileName in FileNames:
    File = open(FileName)

    # get Header row
    for Line in File:
        Header = Line
        break

    FileCount = 0
    Linecount = 1
    for Line in File:

        #skip Header in File
        if Line == Header:
            continue

        #create NewFile with Header every [LinesPerFile] Lines
        if Linecount % LinesPerFile == 1:
            FileCount = FileCount + 1
            NewFileName = FileName[:FileName.find('.')] + '-Part' + str(FileCount) + FileName[FileName.find('.'):]
            NewFile = open(NewFileName,'w')
            NewFile.write(Header)

        NewFile.write(Line)
        Linecount = Linecount + 1

    NewFile.close()

或者,wc和split的python版本:

lines = 0
for l in open(filename): lines += 1

然后编写一些代码,将第一行/3读入一个文件,将下一行/3读入另一个文件,以此类推。