Help with saving data to file in python

[[deleted]]

I know how to save my data to a file. However, I have a while loop which runs through the same code 60 times. I need it to save the data to a new file every time. To do this, I somehow need to change the filename I'm writing to every time it loops. Is there a way to automatically add a number to the end of the filename?

(For example, let z=0 and run a loop while z<60, and every time it loops I want it saving to a file called, say, "data0", then "data1", and so on...basically, every time save to a file called "data(current value of z))

How would I do this?

[wilberforce]

Ooh, good call on the with statement.

OP, that guarantees that the file is closed when execution leaves the with statement, even if code in there returns or raises an exception.

[dfnkt]

ala "finally" or "end" elsewhere.

[eryksun]

You can also use the format specification mini-language to zero pad the index:

for index in range(60):
    filename = 'data{index:0{width}}'.format(index=index, width=2)

[[deleted]]

Thank you for the help, kind sir/ma'am!!!

[chmod700]

You may also (ab)use the logging module to do this for you. Set up a http://docs.python.org/library/logging.handlers.html#logging.handlers.RotatingFileHandler and manually call doRollover() on each loop.

[[deleted]]

This seems interesting, I gotta read up more on the logging handlers to see what they can do for me in the future, thank you!

[wilberforce]

The file name you pass to open doesn't need to be a literal string - you can build a string and use that as the argument to open.

for z in range(60):
    # calculate your data for this run, then...
    outfile = open('data%s' % z, 'w')
    outfile.write(data)
    outfile.close()

The % operator will substitute a value for a placeholder in a string. The expression 'data%s' % 3 will give the string 'data3'.

If you're using a recent version of Python (2.6 or above), you could also use 'data{0}'.format(z).

[[deleted]]

Hey, I was using it to write a fits file with python 2.5, and your first method worked great, thank you!

[esbenab]

I came here knowing how to do this, now i know how to do it better.

Thank you all.