How to open a file for both reading and writing?
PythonFileFile IoPython Problem Overview
Is there a way to open a file for both reading and writing?
As a workaround, I open the file for writing, close it, then open it again for reading. But is there a way to open a file for both reading and writing?
Python Solutions
Solution 1 - Python
Here's how you read a file, and then write to it (overwriting any existing data), without closing and reopening:
with open(filename, "r+") as f:
data = f.read()
f.seek(0)
f.write(output)
f.truncate()
Solution 2 - Python
Summarize the I/O behaviors
| Mode | r | r+ | w | w+ | a | a+ |
|---|---|---|---|---|---|---|
| Read | + | + | + | + | ||
| Write | + | + | + | + | + | |
| Create | + | + | + | + | ||
| Cover | + | + | ||||
| Point in the beginning | + | + | + | + | ||
| Point in the end | + | + |
and the decision branch
Solution 3 - Python
r+ is the canonical mode for reading and writing at the same time. This is not different from using the fopen() system call since file() / open() is just a tiny wrapper around this operating system call.
Solution 4 - Python
I have tried something like this and it works as expected:
f = open("c:\\log.log", 'r+b')
f.write("\x5F\x9D\x3E")
f.read(100)
f.close()
Where:
> f.read(size) - To read a file’s contents, call f.read(size), which > reads some quantity of data and returns it as a string.
And:
> f.write(string) writes the contents of string to the file, returning > None.
Also if you open Python tutorial about reading and writing files you will find that:
> 'r+' opens the file for both reading and writing. > > On Windows, 'b' appended to the mode opens the file in binary mode, so > there are also modes like 'rb', 'wb', and 'r+b'.