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The following test script demonstrates that Python's csv library does not handle a BOM. I would expect the returned row to be equal to expected and to print 'True' to stdout.
In the wild, it is typical for other CSV writers to add a BOM. MS Excel is especially picky about the BOM when reading a utf-8 encoded file. So many writers add a BOM for interopability with MS Excel.
If a python program accepts a CSV file as input (often the case in web apps), these files will not be handled correctly without preprocessing. In my opinion, this should "just work" when reading the file.
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import codecs
import csv
f = open('foo.csv', 'wb')
f.write(codecs.BOM_UTF8 + b'a,b,c')
f.close()
expected = ['a', 'b', 'c']
f = open('foo.csv')
r = csv.reader(f)
row = next(r)
print(row)
print(row == expected)
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Output
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$ ./python ~/test.py
['\ufeffa', 'b', 'c']
False
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This is not a problem with the csv module in particular. See issue 7651.