[Tutor] Help with printing to text file

[Steven D'Aprano]

On Mon, Feb 01, 2016 at 08:41:31PM +0000, Alan Gauld wrote:
> On 01/02/16 14:07, Chelsea G wrote:
> > Hi,
> > 
> > So I am trying to get my function search to print  in a text file, but I
> > can only get it to print to Powershell. I have tried several things to get
> > it to print in its own text file but nothing I have tried is working. Can
> > someone tell me what I am doing wrong?

> That's because print sends its output to the standard out.
> You need to store your results somewhere (maybe in a list?) and
> then write() those results to a file.

You don't even need to do that! print has a secret (well, not really a 
secret, but you would be amazed how few people know about it) option to 
print directly to an open file.

In Python 3 you write:

    print("Hello World!", file=output_file)

but in Python 2 you must use this ugly syntax instead:

    print >>output_file, "Hello World!"

output_file must be already opened for writing, of course.

So Chelsea's class would become something like this:


class dictionary:
	...
	def search(self, filename):
		with open('weekly_test.csv', 'r') as searchfile, open('testdoc.txt', 'w') as text_file:
			for line in searchfile:
				if 'PBI 43125' in line:
					print >>text_file, line



By the way, the argument "filename" is not used here. Is that 
intentional?


But perhaps an even better solution is to use the environment's file 
redirection. Powershell should understand > to mean "print to a file", 
so you can write:

    python myscript.py 

to have myscript print output directly to the terminal window, and then:

    python myscript.py > testdoc.txt

to redirect the output and write it to testdoc.txt instead. 



-- 
Steve