#PYTHON WRITE TO FILE HOW TO#
#PYTHON WRITE TO FILE CODE#

with contextlib you can write context managers through functions(actually generators) as well. if you want to do more research on context managers surely you can do it and note that writing classes are not the only way to write context managers. honestly, I don't know the use of the third variable, but for me, the first two are enough. for example, exc_type: TypeErrorĮxc_value: unsupported operand type(s) for +: 'int' and 'strįrom the first two variables, you can get info enough info about the error. exc_type, exc_value, exc_traceback variables are the variables that hold the values of the errors that occurred inside with block.

#PYTHON WRITE TO FILE CODE#

The last method is the method to run after an error is captured or if the code exits the with block.

what it returns is the value to be assigned to the variable after the as keyword. some of you might not have seen it because it is a specific method for context managers. The second method _enter_ is a bit interesting. and that's the place where you put your all the init kinda code. whenever an object is created obj._init_ is definitely called. The first method _init_ is (as you all know) the initialization method of an object. class FileOpenerCM:ĭef _exit_(self, exc_type, exc_value, exc_traceback): so let's see how this happens under the hood. This is a so-called context manager, anything that comes with a with block is a context manager. with FileOpenerCM('file.txt') as fp: # is equal to 'with open('file.txt') as fp:'

#PYTHON WRITE TO FILE HOW TO#

Since others have answered how to do it, I'll answer how it happens line by line. If you need to concatenate a bunch of strings to get this loooong line performance will suffer, so use-cases where print would be more efficient are a bit rare. The performance difference now becomes much less pronounced, with an average time of 2.20s for write and 3.10s for print. A simple test for this would be to check performance for long writes as well, where the disadvantages (in terms of speed) for line buffering would be less pronounced. Update: This difference in performance is explained by the fact that write is highly buffered and returns before any writes to disk actually take place (see this answer), whereas print (probably) uses line buffering. Whichever way you choose I'd suggest using with since it makes the code much easier to read. This can be done by setting the optional end parameter, e.g. If you choose to go with print(., file=f) you will probably find that you'll want to suppress the newline from time to time, or replace it with something else. That being said, in most real-world scenarios this will not be an issue. On average write finished in 2.45s on my machine, whereas print took about 4 times as long (9.76s). I did a quick speed comparison and it was considerably faster than print(., file=f) when performing a large number of writes. If you are writing a lot of data and speed is a concern you should probably go with f.write(.). There is no point in using os.linesep on non-Windows systems, and it produces wrong results on Windows. And it's been that simple ever since the first port of Python to Windows. It's this simple: use which will be translated automatically to os.linesep. 'hi there' + os.linesep is equivalent to 'hi there ', which is NOT equivalent to 'hi there '. There is no way that it could produce the same outcome. > f.write('hi there' + os.linesep) # same result as previous line ?Īs expected, os.linesep does NOT produce the same outcome as ' '.

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Python write to file