Python: Keep savefig from overwriting old plots

matplotlib, operating-system, python

Solution

You'll have to provide some unique name yourself: matplotlib won't do it for you. Nor will matplotlib check for existence of your current filename. I would write a loop along the following lines:

(untested code)

import os
i = 0
while True:
    i += 1
    newname = '{}{:d}.png'.format(filename, i)
    if os.path.exists(newname):
        continue
    plt.savefig(newname)
    break

Note: if the extension is already `.png`, you don't need to set the format to `png` explicitly.

Edit

I realized the above is too long-winded, and only came about because I wanted to avoid doing the string formatting twice. The following is probably more logical:

import os
i = 0
while os.path.exists('{}{:d}.png'.format(filename, i)):
    i += 1
plt.savefig('{}{:d}.png'.format(filename, i))

Problem

I simply use ``` plt.savefig(filename+'.png', format='png') ``` to save my plots. But I want to keep my old versions of `filename.png` when I create a new one (using different colour codes, etc.) without always having to come up with a new filename. Since I don't do that in one run, this doesn't help me. I found this on how to keep Python from overwriting files, but that's for `os`. Is there a way to do this with `savefig`? In the end I want Python to check whether `filename.png` exists and only if so, save the new figure as `filename1.png`, `filename2.png`, etc.

Original source

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