Python 2.7: UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode

[ndbroadbent]

I'm running py.test and seeing the following warnings:

  /usr/local/lib/python2.7/site-packages/piexif/_load.py:67: UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode - interpreting them as being unequal
    if data[0:2] == b"\xff\xd8":  # JPEG

tests/test_download_photos.py::DownloadPhotoTestCase::test_download_photos_and_set_exif
  /usr/local/lib/python2.7/site-packages/piexif/_insert.py:22: UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode - interpreting them as being unequal
    if image[0:2] == b"\xff\xd8":

-- Docs: http://doc.pytest.org/en/latest/warnings.html

[ndbroadbent]

Reading up on byte literals: https://stackoverflow.com/a/6269785/304706

A prefix of 'b' or 'B' is ignored in Python 2; it indicates that the literal should become a bytes literal in Python 3 (e.g. when code is automatically converted with 2to3). A 'u' or 'b' prefix may be followed by an 'r' prefix.

Does this mean that Piexif will not work on Python 2?

Just trying to figure out this unicode warning because it's making my tests a bit noisy. And also I'm starting to think that the comparisons are actually broken in Python 2, so it might not even be working.

[ndbroadbent]

I was able to remove the warning by changing /usr/local/lib/python2.7/site-packages/piexif/_load.py:67 to:

if data[0:2] == u"\xff\xd8":  # JPEG

(instead of b"\xff\xd8".)

But I'm actually not sure if that is the correct behavior. Maybe the type of data needs to be changed so that it is not unicode?

[ndbroadbent]

Oh wow, just reading through the code, I realized that data is actually the filename I'm passing in, and not the file data!

class _ExifReader(object):
    def __init__(self, data):
        if data[0:2] == b"\xff\xd8":  # JPEG

So it first checks to see if the filename string is an image, and if that fails, then it tries to open the string as a file path. So I think it's safe to say that in Python 2.7, if data is a unicode string, then it's not going to be some image data. However, a non-unicode string might be data OR a filename.

[ndbroadbent]

Fixed these warnings with a PR in #68

[hMatoba]

Thank you for sending pull request. But I'm using unittest and have no problem. https://travis-ci.org/hMatoba/Piexif/builds/402180473

[ndbroadbent]

Hello, yes this not an error, but python shows a warning in the console. It is happening because I am passing filename strings that have unicode characters. For example:

exif_dict = piexif.load("./相片/photo.jpg")

This works fine on Python 3 but shows a warning on Python 2.7

[jdpiguet]

I have the same problem with Python 2.7 (Linux Mint). It happens if the file name is a Unicode string. `jdp@amroth:~$ python Python 2.7.12 (default, Nov 12 2018, 14:36:49) [GCC 5.4.0 20160609] on linux2 Type "help", "copyright", "credits" or "license" for more information.

import piexif filepath = u'/net/gandalf/srv/photos/Camino/2017/test/20170826_111047.jpg' exif_datas = piexif.load(filepath) /usr/local/lib/python2.7/dist-packages/piexif/_load.py:67: UnicodeWarning: Unicode equal comparison failed to convert both arguments to Unicode - interpreting them as being unequal if data[0:2] == b"\xff\xd8": # JPEG

`