99

リストをファイルに書き込むプログラムがあります。リストはパイプで区切られた行のリストであり、行は次のようにファイルに書き込む必要があります。

123|GSV|Weather_Mean|hello|joe|43.45
122|GEV|temp_Mean|hello|joe|23.45
124|GSI|Weather_Mean|hello|Mike|47.45

しかし、それは彼らにこのahhhhの行を書いた：

123|GSV|Weather_Mean|hello|joe|43.45122|GEV|temp_Mean|hello|joe|23.45124|GSI|Weather_Mean|hello|Mike|47.45

このプログラムは、すべての行を改行なしで1行のように書き込みました。これは私を非常に傷つけ、これを逆にする方法を理解する必要がありますが、とにかく、私のプログラムはここで間違っていますか？書き込み行は、すべてを1行に書き込むのではなく、ファイルに行を書き込む必要があると思いました。

fr = open(sys.argv[1], 'r') # source file
fw = open(sys.argv[2]+"/masked_"+sys.argv[1], 'w') # Target Directory Location

for line in fr:
    line = line.strip()
    if line == "":
        continue
    columns = line.strip().split('|')
    if columns[0].find("@") > 1:
        looking_for = columns[0] # this is what we need to search
    else:
        looking_for = "Dummy@dummy.com"
    if looking_for in d:
        # by default, iterating over a dictionary will return keys
            new_line = d[looking_for]+'|'+'|'.join(columns[1:])
            line_list.append(new_line)
    else:
        new_idx = str(len(d)+1)
        d[looking_for] = new_idx
        kv = open(sys.argv[3], 'a')
        kv.write(looking_for+" "+new_idx+'\n')
        kv.close()
        new_line = d[looking_for]+'|'+'|'.join(columns[1:])
        line_list.append(new_line)
fw.writelines(line_list)
4

8 に答える 8

79

This is actually a pretty common problem for newcomers to Python—especially since, across the standard library and popular third-party libraries, some reading functions strip out newlines, but almost no writing functions (except the log-related stuff) add them.

So, there's a lot of Python code out there that does things like:

fw.write('\n'.join(line_list) + '\n')

or

fw.write(line + '\n' for line in line_list)

Either one is correct, and of course you could even write your own writelinesWithNewlines function that wraps it up…</p>

But you should only do this if you can't avoid it.

It's better if you can create/keep the newlines in the first place—as in Greg Hewgill's suggestions:

line_list.append(new_line + "\n")

And it's even better if you can work at a higher level than raw lines of text, e.g., by using the csv module in the standard library, as esuaro suggests.

For example, right after defining fw, you might do this:

cw = csv.writer(fw, delimiter='|')

Then, instead of this:

new_line = d[looking_for]+'|'+'|'.join(columns[1:])
line_list.append(new_line)

You do this:

row_list.append(d[looking_for] + columns[1:])

And at the end, instead of this:

fw.writelines(line_list)

You do this:

cw.writerows(row_list)

Finally, your design is "open a file, then build up a list of lines to add to the file, then write them all at once". If you're going to open the file up top, why not just write the lines one by one? Whether you're using simple writes or a csv.writer, it'll make your life simpler, and your code easier to read. (Sometimes there can be simplicity, efficiency, or correctness reasons to write a file all at once—but once you've moved the open all the way to the opposite end of the program from the write, you've pretty much lost any benefits of all-at-once.)

于 2012-12-05T18:52:01.497 に答える
53

状態のドキュメントwritelines():

writelines()行区切りを追加しません

そのため、それらを自分で追加する必要があります。例えば：

    line_list.append(new_line + "\n")

に新しいアイテムを追加するたびにline_list。

于 2012-12-05T18:44:58.233 に答える
9

writelines()行区切りを追加しません。map()を使用して各文字列の末尾に新しい\n(改行)を追加することにより、文字列のリストを変更できます。

items = ['abc', '123', '!@#']
items = map(lambda x: x + '\n', items)
w.writelines(items)
于 2016-11-13T14:52:33.133 に答える