如果你只想合并两个文件file1.csv和file2.csv，那么标准库模块shutil中的copyfileobj为大文件提供了一个有效的方法（带分块）：

from shutil import copyfileobj

with open("combined.csv", "w") as fout:
    for file in "file1.csv", "file2.csv":
        with open(file, "r") as fin:
            copyfileobj(fin, fout)

如果文件不是很大，你也可以这样做：

with open("combined.csv", "w") as fout:
    for file in "file1.csv", "file2.csv":
        with open(file, "r") as fin:
            fout.write(fin.read())

如果从1.到2.文件的转换由于1.文件的最后一行内容的末尾缺少换行符而变得混乱，您可以将代码的最后一行替换为：

...
            fout.write(fin.read().rstrip("\n") + "\n")

现在，如果文件太大 * 并且 * 转换变得混乱，您可以执行以下操作：

from fileinput import input as finput

with open("combined.csv", "w") as fout,\
     finput(["file1.csv", "file2.csv"]) as fin:
         line = next(fin)
         fout.write(line)
         for next_line in fin:
            if fin.isfirstline() and not line.endswith("\n"):
                next_line = "\n" + next_line
            fout.write(next_line)
            line = next_line

标准库模块fileinput中的input函数提供了一种方便的方法来遍历文件序列的所有行，并对当前位置在序列中的位置进行一些控制检查。
或者你可以使用标准库中的csv模块：

import csv

with open("combined.csv", "w") as fout:
    writer = csv.writer(fout)
    for file in "file1.csv", "file2.csv":
        with open(file, "r") as fin:
            writer.writerows(csv.reader(fin))