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How do I concatenate text files in Python?

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How do I combine multiple text files into one?

Two quick options for combining text files.Open the two files you want to merge. Select all text (Command+A/Ctrl+A) from one document, then paste it into the new document (Command+V/Ctrl+V). Repeat steps for the second document. This will finish combining the text of both documents into one.

How do you concatenate a file?

To choose the merge option, click the arrow next to the Merge button and select the desired merge option. Once complete, the files are merged. If there are multiple files you want to merge at once, you can select multiple files by holding down the Ctrl and selecting each file you want to merge.


This should do it

For large files:

filenames = ['file1.txt', 'file2.txt', ...]
with open('path/to/output/file', 'w') as outfile:
    for fname in filenames:
        with open(fname) as infile:
            for line in infile:
                outfile.write(line)

For small files:

filenames = ['file1.txt', 'file2.txt', ...]
with open('path/to/output/file', 'w') as outfile:
    for fname in filenames:
        with open(fname) as infile:
            outfile.write(infile.read())

… and another interesting one that I thought of:

filenames = ['file1.txt', 'file2.txt', ...]
with open('path/to/output/file', 'w') as outfile:
    for line in itertools.chain.from_iterable(itertools.imap(open, filnames)):
        outfile.write(line)

Sadly, this last method leaves a few open file descriptors, which the GC should take care of anyway. I just thought it was interesting


Use shutil.copyfileobj.

It automatically reads the input files chunk by chunk for you, which is more more efficient and reading the input files in and will work even if some of the input files are too large to fit into memory:

import shutil

with open('output_file.txt','wb') as wfd:
    for f in ['seg1.txt','seg2.txt','seg3.txt']:
        with open(f,'rb') as fd:
            shutil.copyfileobj(fd, wfd)

That's exactly what fileinput is for:

import fileinput
with open(outfilename, 'w') as fout, fileinput.input(filenames) as fin:
    for line in fin:
        fout.write(line)

For this use case, it's really not much simpler than just iterating over the files manually, but in other cases, having a single iterator that iterates over all of the files as if they were a single file is very handy. (Also, the fact that fileinput closes each file as soon as it's done means there's no need to with or close each one, but that's just a one-line savings, not that big of a deal.)

There are some other nifty features in fileinput, like the ability to do in-place modifications of files just by filtering each line.


As noted in the comments, and discussed in another post, fileinput for Python 2.7 will not work as indicated. Here slight modification to make the code Python 2.7 compliant

with open('outfilename', 'w') as fout:
    fin = fileinput.input(filenames)
    for line in fin:
        fout.write(line)
    fin.close()

I don't know about elegance, but this works:

    import glob
    import os
    for f in glob.glob("file*.txt"):
         os.system("cat "+f+" >> OutFile.txt")

What's wrong with UNIX commands ? (given you're not working on Windows) :

ls | xargs cat | tee output.txt does the job ( you can call it from python with subprocess if you want)


outfile.write(infile.read()) # time: 2.1085190773010254s
shutil.copyfileobj(fd, wfd, 1024*1024*10) # time: 0.60599684715271s

A simple benchmark shows that the shutil performs better.