str/bytes problems

[srittau]

While writing type stubs for ExifRead (python/typeshed#9403), I've come across a few inconsistencies/bugs that are probably related to the str/bytes changes from Python 2 to Python 3.

1. ord_ is only ever called with a bytes argument, but checks for a str and returns a bytes argument unchanged:

exif-py/exifread/utils.py

Lines 9 to 12 in 51d5c5a

	def ord_(dta):
	if isinstance(dta, str):
	return ord(dta)
	return dta

I believe this method is mostly obsolete and could be replaced by straight calls to ord().

2. special_mode() in tags/makernote/olympus.py is (I think) passed a bytes string and returns a regular str. But in the case where the passed in string is empty, it will just return it unchanged (i.e. it will return bytes instead of str), possibly raise a TypeError:

exif-py/exifread/tags/makernote/olympus.py

Lines 5 to 26 in 51d5c5a

	def special_mode(val):
	"""Decode Olympus SpecialMode tag in MakerNote"""
	mode1 = {
	0: 'Normal',
	1: 'Unknown',
	2: 'Fast',
	3: 'Panorama',
	}
	mode2 = {
	0: 'Non-panoramic',
	1: 'Left to right',
	2: 'Right to left',
	3: 'Bottom to top',
	4: 'Top to bottom',
	}
	if not val:
	return val
	mode1_val = mode1.get(val[0], "Unknown")
	mode2_val = mode2.get(val[2], "Unknown")
	return '%s - Sequence %d - %s' % (mode1_val, val[1], mode2_val)