如何在Python中添加文件?

如何追加文件而不是覆盖它?是否有一个附加到文件的特殊函数?

1 2	with open("test.txt","a") as myfile: myfile.write("appended text")

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您需要在追加模式下打开文件，将"a"或"ab"设置为模式。看到open ()。

当您以"a"模式打开时，写入位置始终位于文件的末尾(追加)。您可以使用"a+"打开以允许读取、向后查找和读取(但是所有的写操作仍然位于文件的末尾!)

例子:

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>>> with open('test1','wb') as f:
f.write('test')
>>> with open('test1','ab') as f:
f.write('koko')
>>> with open('test1','rb') as f:
f.read()
'testkoko'

注意:使用"a"与使用"w"打开文件并查找文件末尾是不一样的—请考虑如果另一个程序打开文件并在查找和写入之间开始写入，可能会发生什么情况。在一些操作系统上，用"a"打开文件可以保证所有后面的写操作都会自动附加到文件末尾(即使文件是通过其他写操作增长的)。

关于"A"模式如何操作的更多细节(仅在Linux上测试)。即使你往回找，每次写都会追加到文件的末尾:

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>>> f = open('test','a+') # Not using 'with' just to simplify the example REPL session
>>> f.write('hi')
>>> f.seek(0)
>>> f.read()
'hi'
>>> f.seek(0)
>>> f.write('bye') # Will still append despite the seek(0)!
>>> f.seek(0)
>>> f.read()
'hibye'

事实上，fopen手册说:

Opening a file in append mode (a as the first character of mode)
causes all subsequent write operations to this stream to occur at
end-of-file, as if preceded the call:

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fseek(stream, 0, SEEK_END);

旧的简化答案(不使用with):

示例:(在实际程序中使用with关闭文件-请参阅文档)

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>>> open("test","wb").write("test")
>>> open("test","a+b").write("koko")
>>> open("test","rb").read()
'testkoko'

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我总是这样做，

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f = open('filename.txt', 'a')
f.write("stuff")
f.close()

它很简单，但是非常有用。

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您可能希望传递"a"作为模式参数。有关open()，请参阅文档。

1 2	with open("foo","a") as f: f.write("cool beans...")

对于update(+)、truncating (w)和binary (b)模式，还有其他模式参数的排列，但是最好从"a"开始。

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Python在主要的三种模式之外有很多变化，这三种模式是:

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'w' write text
'r' read text
'a' append text

因此，添加到文件中很简单:

1 2	f = open('filename.txt', 'a') f.write('whatever you want to write here (in append mode) here.')

还有一些模式可以让你的代码行数更少:

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'r+' read + write text
'w+' read + write text
'a+' append + read text

最后，还有二进制格式的读/写模式:

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'rb' read binary
'wb' write binary
'ab' append binary
'rb+' read + write binary
'wb+' read + write binary
'ab+' append + read binary

当我们使用这一行open(filename,"a")时，a表示附加文件，这意味着允许向现有文件插入额外的数据。

您可以使用以下几行来在文件中附加文本

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def FileSave(filename,content):
with open(filename,"a") as myfile:
myfile.write(content)

FileSave("test.txt","test1
")
FileSave("test.txt","test2
")

您还可以以r+模式打开文件，然后将文件位置设置为文件的末尾。

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import os

with open('text.txt', 'r+') as f:
f.seek(0, os.SEEK_END)
f.write("text to add")

以r+模式打开文件将允许您写入文件末尾之外的其他位置，而a和a+强制写入文件末尾。

如果要附加到文件中

1 2	with open("test.txt","a") as myfile: myfile.write("append me")

我们声明变量myfile来打开一个名为test.txt的文件。Open接受两个参数，一个是要打开的文件，另一个是表示要对文件执行的权限或操作类型的字符串

下面是文件模式选项

Mode    Description

'r' This is the default mode. It Opens file for reading.
'w' This Mode Opens file for writing. 
If file does not exist, it creates a new file.
If file exists it truncates the file.
'x' Creates a new file. If file already exists, the operation fails.
'a' Open file in append mode. 
If file does not exist, it creates a new file.
't' This is the default mode. It opens in text mode.
'b' This opens in binary mode.
'+' This will open a file for reading and writing (updating)

这是我的脚本，它基本上是计算行数，然后追加，然后再计算一次，这样你就有了它工作的证据。

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shortPath ="../file_to_be_appended"
short = open(shortPath, 'r')

## this counts how many line are originally in the file:
long_path ="../file_to_be_appended_to"
long = open(long_path, 'r')
for i,l in enumerate(long):
pass
print"%s has %i lines initially" %(long_path,i)
long.close()

long = open(long_path, 'a') ## now open long file to append
l = True ## will be a line
c = 0 ## count the number of lines you write
while l:
try:
l = short.next() ## when you run out of lines, this breaks and the except statement is run
c += 1
long.write(l)

except:
l = None
long.close()
print"Done!, wrote %s lines" %c

## finally, count how many lines are left.
long = open(long_path, 'r')
for i,l in enumerate(long):
pass
print"%s has %i lines after appending new lines" %(long_path, i)
long.close()