blocks|key|1530103|text|这取决于你想做什么。要追加，可以用“a”打开它：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1530104|+with+open("foo.txt",+"a")+as+f:
+++++f.write("new+line\n")|code-block|syntax|javascript|1530105|如果你想预先准备一些东西，你必须先从文件中读取：|1530106|with+open("foo.txt",+"r%2B")+as+f:
+++++old+=+f.read()+#+read+everything+in+the+file
+++++f.seek(0)+#+rewind
+++++f.write("new+line\n"+%2B+old)+#+write+the+new+line+before|1530107|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Depends on what you want to do. To append you can open it with "a":

<pre><code> with open("foo.txt", "a") as f:
 f.write("new line\n")
</code></pre>

If you want to preprend something you have to read from the file first:

<pre><code>with open("foo.txt", "r+") as f:
 old = f.read() # read everything in the file
 f.seek(0) # rewind
 f.write("new line\n" + old) # write the new line before
</code></pre>

blocks|key|1745123|text|不幸的是，没有办法在不重写文件的情况下插入到文件的中间。正如之前的帖子所指出的那样，你可以使用seek添加到一个文件中或覆盖它的一部分，但如果你想在开始或中间添加东西，你必须重写它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1745124|这是操作系统的问题，不是Python的问题。这在所有语言中都是一样的。|1745125|我通常做的是从文件中读取，进行修改，并将其写出到一个名为myfile.txt.tmp或类似的新文件中。这比将整个文件读取到内存中要好，因为文件可能太大了。完成临时文件后，我将其重命名为与原始文件相同的名称。|1745126|这是一种很好的、安全的方法，因为如果文件写入由于任何原因而崩溃或中止，您仍然可以保留未被修改的原始文件。|1745127|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

Unfortunately there is no way to insert into the middle of a file without re-writing it. As previous posters have indicated, you can append to a file or overwrite part of it using seek but if you want to add stuff at the beginning or the middle, you'll have to rewrite it.

This is an operating system thing, not a Python thing. It is the same in all languages.

What I usually do is read from the file, make the modifications and write it out to a new file called myfile.txt.tmp or something like that. This is better than reading the whole file into memory because the file may be too large for that. Once the temporary file is completed, I rename it the same as the original file.

This is a good, safe way to do it because if the file write crashes or aborts for any reason, you still have your untouched original file.

blocks|key|1530238|text|就地重写文件通常是通过使用修改的名称保存旧副本来完成的。Unix的人会添加一个~来标记旧的。Windows用户可以做各种事情--添加.bak或.old+--或者完全重命名文件，或者将~放在文件名的前面。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1530239|import+shutil
shutil.move(+afile,+afile%2B"~"+)

destination=+open(+aFile,+"w"+)
source=+open(+aFile%2B"~",+"r"+)
for+line+in+source:
++++destination.write(+line+)
++++if+<some+condition>:
++++++++destination.write(+>some+additional+line>+%2B+"\n"+)
source.close()
destination.close()|code-block|syntax|javascript|1530240|您可以使用以下代码来代替shutil。|1530241|import+os
os.rename(+aFile,+aFile%2B"~"+)|1530242|entityMap^0|13|1|0|0|C|6|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

Rewriting a file in place is often done by saving the old copy with a modified name. Unix folks add a <code>~</code> to mark the old one. Windows folks do all kinds of things -- add .bak or .old -- or rename the file entirely or put the ~ on the front of the name.

<pre><code>import shutil
shutil.move( afile, afile+"~" )

destination= open( aFile, "w" )
source= open( aFile+"~", "r" )
for line in source:
 destination.write( line )
 if &lt;some condition&gt;:
 destination.write( &gt;some additional line&gt; + "\n" )
source.close()
destination.close()
</code></pre>

Instead of <code>shutil</code>, you can use the following.

<pre><code>import os
os.rename( aFile, aFile+"~" )
</code></pre>

blocks|key|1745276|text|Python的mmap模块将允许您插入到文件中。下面的示例展示了如何在Unix中实现(Windows+mmap可能有所不同)。请注意，这并不能处理所有错误情况，并且您可能会损坏或丢失原始文件。此外，这不会处理unicode字符串。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1745277|import+os
from+mmap+import+mmap

def+insert(filename,+str,+pos):
++++if+len(str)+<+1:
++++++++#+nothing+to+insert
++++++++return

++++f+=+open(filename,+'r%2B')
++++m+=+mmap(f.fileno(),+os.path.getsize(filename))
++++origSize+=+m.size()

++++#+or+this+could+be+an+error
++++if+pos+>+origSize:
++++++++pos+=+origSize
++++elif+pos+<+0:
++++++++pos+=+0

++++m.resize(origSize+%2B+len(str))
++++m[pos%2Blen(str):]+=+m[pos:origSize]
++++m[pos:pos%2Blen(str)]+=+str
++++m.close()
++++f.close()|code-block|syntax|javascript|1745278|也可以在没有mmap的情况下使用'r%2B‘模式打开的文件，但这样做不太方便，效率也较低，因为您必须读取文件的内容并将其从插入位置临时存储到EOF+-这可能会很大。|1745279|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Python's mmap module will allow you to insert into a file. The following sample shows how it can be done in Unix (Windows mmap may be different). Note that this does not handle all error conditions and you might corrupt or lose the original file. Also, this won't handle unicode strings.

<pre><code>import os
from mmap import mmap

def insert(filename, str, pos):
 if len(str) &lt; 1:
 # nothing to insert
 return

 f = open(filename, 'r+')
 m = mmap(f.fileno(), os.path.getsize(filename))
 origSize = m.size()

 # or this could be an error
 if pos &gt; origSize:
 pos = origSize
 elif pos &lt; 0:
 pos = 0

 m.resize(origSize + len(str))
 m[pos+len(str):] = m[pos:origSize]
 m[pos:pos+len(str)] = str
 m.close()
 f.close()
</code></pre>

It is also possible to do this without mmap with files opened in 'r+' mode, but it is less convenient and less efficient as you'd have to read and temporarily store the contents of the file from the insertion position to EOF - which might be huge.

blocks|key|1745322|text|我写了一个小类来干净利落地做这件事。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1745323|import+tempfile

class+FileModifierError(Exception):
++++pass

class+FileModifier(object):

++++def+__init__(self,+fname):
++++++++self.__write_dict+=+{}
++++++++self.__filename+=+fname
++++++++self.__tempfile+=+tempfile.TemporaryFile()
++++++++with+open(fname,+'rb')+as+fp:
++++++++++++for+line+in+fp:
++++++++++++++++self.__tempfile.write(line)
++++++++self.__tempfile.seek(0)

++++def+write(self,+s,+line_number+=+'END'):
++++++++if+line_number+!=+'END'+and+not+isinstance(line_number,+(int,+float)):
++++++++++++raise+FileModifierError("Line+number+%25s+is+not+a+valid+number"+%25+line_number)
++++++++try:
++++++++++++self.__write_dict[line_number].append(s)
++++++++except+KeyError:
++++++++++++self.__write_dict[line_number]+=+[s]

++++def+writeline(self,+s,+line_number+=+'END'):
++++++++self.write('%25s\n'+%25+s,+line_number)

++++def+writelines(self,+s,+line_number+=+'END'):
++++++++for+ln+in+s:
++++++++++++self.writeline(s,+line_number)

++++def+__popline(self,+index,+fp):
++++++++try:
++++++++++++ilines+=+self.__write_dict.pop(index)
++++++++++++for+line+in+ilines:
++++++++++++++++fp.write(line)
++++++++except+KeyError:
++++++++++++pass

++++def+close(self):
++++++++self.__exit__(None,+None,+None)

++++def+__enter__(self):
++++++++return+self

++++def+__exit__(self,+type,+value,+traceback):
++++++++with+open(self.__filename,'w')+as+fp:
++++++++++++for+index,+line+in+enumerate(self.__tempfile.readlines()):
++++++++++++++++self.__popline(index,+fp)
++++++++++++++++fp.write(line)
++++++++++++for+index+in+sorted(self.__write_dict):
++++++++++++++++for+line+in+self.__write_dict[index]:
++++++++++++++++++++fp.write(line)
++++++++self.__tempfile.close()|code-block|syntax|javascript|1745324|然后你可以这样使用它：|1745325|with+FileModifier(filename)+as+fp:
++++fp.writeline("String+1",+0)
++++fp.writeline("String+2",+20)
++++fp.writeline("String+3")++#+To+write+at+the+end+of+the+file|1745326|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Wrote a small class for doing this cleanly.

<pre><code>import tempfile

class FileModifierError(Exception):
 pass

class FileModifier(object):

 def __init__(self, fname):
 self.__write_dict = {}
 self.__filename = fname
 self.__tempfile = tempfile.TemporaryFile()
 with open(fname, 'rb') as fp:
 for line in fp:
 self.__tempfile.write(line)
 self.__tempfile.seek(0)

 def write(self, s, line_number = 'END'):
 if line_number != 'END' and not isinstance(line_number, (int, float)):
 raise FileModifierError("Line number %s is not a valid number" % line_number)
 try:
 self.__write_dict[line_number].append(s)
 except KeyError:
 self.__write_dict[line_number] = [s]

 def writeline(self, s, line_number = 'END'):
 self.write('%s\n' % s, line_number)

 def writelines(self, s, line_number = 'END'):
 for ln in s:
 self.writeline(s, line_number)

 def __popline(self, index, fp):
 try:
 ilines = self.__write_dict.pop(index)
 for line in ilines:
 fp.write(line)
 except KeyError:
 pass

 def close(self):
 self.__exit__(None, None, None)

 def __enter__(self):
 return self

 def __exit__(self, type, value, traceback):
 with open(self.__filename,'w') as fp:
 for index, line in enumerate(self.__tempfile.readlines()):
 self.__popline(index, fp)
 fp.write(line)
 for index in sorted(self.__write_dict):
 for line in self.__write_dict[index]:
 fp.write(line)
 self.__tempfile.close()
</code></pre>

Then you can use it this way:

<pre><code>with FileModifier(filename) as fp:
 fp.writeline("String 1", 0)
 fp.writeline("String 2", 20)
 fp.writeline("String 3") # To write at the end of the file
</code></pre>

blocks|key|1530431|text|如果您了解一些unix，您可以尝试以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1530432|注意：$表示命令提示符|1530433|假设您有一个内容如下的文件my_data.txt：|1530434|$+cat+my_data.txt
This+is+a+data+file
with+all+of+my+data+in+it.|code-block|syntax|javascript|1530435|然后，您可以使用常用的sed命令来使用os模块|offset|length|style|CODE|1530436|import+os

#+Identifiers+used+are:
my_data_file+=+"my_data.txt"
command+=+"sed+-i+'s/all/none/'+my_data.txt"

#+Execute+the+command
os.system(command)|1530437|如果您不知道sed，请查看它，它非常有用。|1530438|entityMap^0|0|0|0|0|B|3|J|2|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|Z|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|10|8|@$M|11|N|12|O|P]|$M|13|N|14|O|P]]|9|@]|A|$]]|$1|Q|3|R|5|H|7|15|8|@]|9|@]|A|$I|J]]|$1|S|3|T|5|6|7|16|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|V|$]]

If you know some unix you could try the following:

Notes: $ means the command prompt 

Say you have a file my_data.txt with content as such:

<pre><code>$ cat my_data.txt
This is a data file
with all of my data in it.
</code></pre>

Then using the <code>os</code> module you can use the usual <code>sed</code> commands

<pre><code>import os

# Identifiers used are:
my_data_file = "my_data.txt"
command = "sed -i 's/all/none/' my_data.txt"

# Execute the command
os.system(command)
</code></pre>

If you aren't aware of sed, check it out, it is extremely useful.

I'm using Python, and would like to insert a string into a text file without deleting or copying the file. How can I do that?

How to modify a text file?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在使用Python，并且希望在不删除或复制文件的情况下将字符串插入到文本文件中。我该怎么做呢？

问如何修改文本文件？
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问如何修改文本文件？EN