python学习——大文件分割与合并

在平常的生活中，我们会遇到下面这样的情况：

你下载了一个比较大型的游戏（假设有10G），现在想跟你的同学一起玩，你需要把这个游戏拷贝给他。

然后现在有一个问题是文件太大（我们不考虑你有移动硬盘什么的情况），假设现在只有一个2G或4G的优盘，该怎么办呢？

有很多方法，例如winrar压缩的时候分成很多小卷，这里不累述。

在学习python之后，我们自己就可以解决这个问题啦。

我们可以自己写一个脚本去分割合并文件，将文件分割成适合优盘大小的小文件，在拷贝，然后再合并。

import sys,os

kilobytes = 1024
megabytes = kilobytes*1000
chunksize = int(200*megabytes)#default chunksize

def split(fromfile,todir,chunksize=chunksize):
    if not os.path.exists(todir):#check whether todir exists or not
        os.mkdir(todir)          
    else:
        for fname in os.listdir(todir):
            os.remove(os.path.join(todir,fname))
    partnum = 0
    inputfile = open(fromfile,'rb')#open the fromfile
    while True:
        chunk = inputfile.read(chunksize)
        if not chunk:             #check the chunk is empty
            break
        partnum += 1
        filename = os.path.join(todir,('part%04d'%partnum))
        fileobj = open(filename,'wb')#make partfile
        fileobj.write(chunk)         #write data into partfile
        fileobj.close()
    return partnum
if __name__=='__main__':
        fromfile  = input('File to be split?')
        todir     = input('Directory to store part files?')
        chunksize = int(input('Chunksize to be split?'))
        absfrom,absto = map(os.path.abspath,[fromfile,todir])
        print('Splitting',absfrom,'to',absto,'by',chunksize)
        try:
            parts = split(fromfile,todir,chunksize)
        except:
            print('Error during split:')
            print(sys.exc_info()[0],sys.exc_info()[1])
        else:
            print('split finished:',parts,'parts are in',absto)

下面是脚本运行的例子：

我们在F有一个X—MEN1.rar文件，1.26G大小，我们现在把它分割成400000000bit(大约380M)的文件。

Python 3.4.1 (v3.4.1:c0e311e010fc, May 18 2014, 10:45:13) [MSC v.1600 64 bit (AMD64)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
File to be split?F:X-MEN1.rar
Directory to store part files?F:split
Chunksize to be split?400000000
Splitting F:X-MEN1.rar to F:split by 400000000
split finished: 4 parts are in F:split
>>>

这是分割后的文件：

 

 下面是文件合并脚本：

import sys,os

def joinfile(fromdir,filename,todir):
    if not os.path.exists(todir):
        os.mkdir(todir)
    if not os.path.exists(fromdir):
        print('Wrong directory')
    outfile = open(os.path.join(todir,filename),'wb')
    files = os.listdir(fromdir) #list all the part files in the directory
    files.sort()                #sort part files to read in order
    for file in files:
        filepath = os.path.join(fromdir,file)
        infile = open(filepath,'rb')
        data = infile.read()
        outfile.write(data)
        infile.close()
    outfile.close()
if __name__=='__main__':
        fromdir = input('Directory containing part files?')
        filename = input('Name of file to be recreated?')
        todir   = input('Directory to store recreated file?')
        
        try:
            joinfile(fromdir,filename,todir)
        except:
            print('Error joining files:')
            print(sys.exc_info()[0],sys.exc_info()[1])

运行合并脚本，将上面分割脚本分割的文件重组：

Python 3.4.1 (v3.4.1:c0e311e010fc, May 18 2014, 10:45:13) [MSC v.1600 64 bit (AMD64)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
Directory containing part files?F:split
Name of file to be recreated?xman1.rar
Directory to store recreated file?F:
>>>

运行之后可以看到F盘下生成了重组的xman.rar