我认为有两种方法可以解决你想要达到的目标。

1)这是显而易见的，打开文件只读，读入内存，然后用t打开文件，然后写你的更改。

2)使用低级文件处理例程:

# Open file in RW , create if it doesn't exist. *Don't* pass O_TRUNC
 fd = os.open(filename, os.O_RDWR | os.O_CREAT)

希望这能有所帮助。

假设你用一个with语句打开文件，就像你应该做的那样。然后你可以这样从你的文件中读取:

with open('somefile.txt', 'w+') as f:
    # Note that f has now been truncated to 0 bytes, so you'll only
    # be able to read data that you write after this point
    f.write('somedata\n')
    f.seek(0)  # Important: return to the top of the file before reading, otherwise you'll just read an empty string
    data = f.read() # Returns 'somedata\n'

注意f.seek(0)——如果您忘记了这一点，f.read()调用将尝试从文件末尾读取，并返回一个空字符串。

Python中的所有文件模式

r for reading r+ opens for reading and writing (cannot truncate a file) w for writing w+ for writing and reading (can truncate a file) rb for reading a binary file. The file pointer is placed at the beginning of the file. rb+ reading or writing a binary file wb+ writing a binary file a+ opens for appending ab+ Opens a file for both appending and reading in binary. The file pointer is at the end of the file if the file exists. The file opens in the append mode. x open for exclusive creation, failing if the file already exists (Python 3)

如h4z3所述， 在实际应用中， 有时你的数据太大，不能直接加载所有内容，或者你有一个生成器，或者实时传入的数据，你可以使用w+存储在一个文件中，然后读取。

文件被截断了，所以你可以调用read()(不会引发异常，不像使用'w'打开时那样)，但你会得到一个空字符串。

R代表读

W代表写

如果文件存在，R +为读写不删除原始内容，否则引发异常

W +表示删除原始内容，如果文件存在则读写，否则创建文件

例如,

>>> with open("file1.txt", "w") as f:
...   f.write("ab\n")
... 
>>> with open("file1.txt", "w+") as f:
...   f.write("c")
... 

$ cat file1.txt 
c$

>>> with open("file2.txt", "r+") as f:
...   f.write("ab\n")
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IOError: [Errno 2] No such file or directory: 'file2.txt'

>>> with open("file2.txt", "w") as f:
...   f.write("ab\n")
... 
>>> with open("file2.txt", "r+") as f:
...   f.write("c")
... 

$ cat file2.txt 
cb
$