set(())              # set()
set([])              # set()
set((1,))            # {1}
set((1, 2))          # {1, 2}
set([1, 2])          # {1, 2}
set(x for x in y)    # {x for x in y}
set([x for x in y])  # {x for x in y}

dict((a, b) for a, b in y)    # {a: b for a, b in y}
dict([(a, b) for a, b in y])  # {a: b for a, b in y}

'{0} {1}'.format(1, 2)    # '{} {}'.format(1, 2)
'{0}' '{1}'.format(1, 2)  # '{}' '{}'.format(1, 2)

'%s %s' % (a, b)                  # '{} {}'.format(a, b)
'%r %2f' % (a, b)                 # '{!r} {:2f}'.format(a, b)
'%(a)s %(b)s' % {'a': 1, 'b': 2}  # '{a} {b}'.format(a=1, b=2)

u'foo'      # 'foo'
u"foo"      # 'foo'
u'''foo'''  # '''foo'''

# strings with only invalid sequences become raw strings
'\d'    # r'\d'
# strings with mixed valid / invalid sequences get escaped
'\n\d'  # '\n\\d'
# `ur` is not a valid string prefix in python3
u'\d'   # u'\\d'

# this fixes a syntax error in python3.3+
'\N'    # r'\N'

# note: pyupgrade is timid in one case (that's usually a mistake)
# in python2.x `'\u2603'` is the same as `'\\u2603'` without `unicode_literals`
# but in python3.x, that's our friend ☃

x is 5      # x == 5
x is not 5  # x != 5
x is 'foo'  # x == foo

ur'foo'         # u'foo'
ur'\s'          # u'\\s'
# unicode escapes are left alone
ur'\u2603'      # u'\u2603'
ur'\U0001f643'  # u'\U0001f643'

'foo'.encode()           # b'foo'
'foo'.encode('ascii')    # b'foo'
'foo'.encode('utf-8')    # b'foo'
u'foo'.encode()          # b'foo'
'\xa0'.encode('latin1')  # b'\xa0'

5L                            # 5
5l                            # 5
123456789123456789123456789L  # 123456789123456789123456789

print(())                       # ok: printing an empty tuple
print((1,))                     # ok: printing a tuple
sum((i for i in range(3)), [])  # ok: parenthesized generator argument
print(("foo"))                  # print("foo")

class C(Base):
    def f(self):
        super(C, self).f()   # super().f()

class C(object): pass     # class C: pass
class C(B, object): pass  # class C(B): pass

str()       # "''"
str("foo")  # "foo"

"foo".encode("utf-8")  # "foo".encode()

def f():
    for x in y:       # yield from y
        yield x

    for a, b in c:    # yield from c
        yield (a, b)

# input
if six.PY2:      # also understands `six.PY3` and `not` and `sys.version_info`
    print('py2')
else:
    print('py3')
# output
print('py3')

six.text_type             # str
six.binary_type           # bytes
six.class_types           # (type,)
six.string_types          # (str,)
six.integer_types         # (int,)
six.unichr                # chr
six.iterbytes             # iter
six.print_(...)           # print(...)
six.exec_(c, g, l)        # exec(c, g, l)
six.advance_iterator(it)  # next(it)
six.next(it)              # next(it)
six.callable(x)           # callable(x)

from six import text_type
text_type                 # str

@six.python_2_unicode_compatible  # decorator is removed
class C:
    def __str__(self):
        return u'C()'

class C(six.Iterator): pass              # class C: pass

class C(six.with_metaclass(M, B)): pass  # class C(B, metaclass=M): pass

@six.add_metaclass(M)   # class C(B, metaclass=M): pass
class C(B): pass

isinstance(..., six.class_types)    # isinstance(..., type)
issubclass(..., six.integer_types)  # issubclass(..., int)
isinstance(..., six.string_types)   # isinstance(..., str)

six.b('...')                            # b'...'
six.u('...')                            # '...'
six.byte2int(bs)                        # bs[0]
six.indexbytes(bs, i)                   # bs[i]
six.int2byte(i)                         # bytes((i,))
six.iteritems(dct)                      # dct.items()
six.iterkeys(dct)                       # dct.keys()
six.itervalues(dct)                     # dct.values()
next(six.iteritems(dct))                # next(iter(dct.items()))
next(six.iterkeys(dct))                 # next(iter(dct.keys()))
next(six.itervalues(dct))               # next(iter(dct.values()))
six.viewitems(dct)                      # dct.items()
six.viewkeys(dct)                       # dct.keys()
six.viewvalues(dct)                     # dct.values()
six.create_unbound_method(fn, cls)      # fn
six.get_unbound_method(meth)            # meth
six.get_method_function(meth)           # meth.__func__
six.get_method_self(meth)               # meth.__self__
six.get_function_closure(fn)            # fn.__closure__
six.get_function_code(fn)               # fn.__code__
six.get_function_defaults(fn)           # fn.__defaults__
six.get_function_globals(fn)            # fn.__globals__
six.assertCountEqual(self, a1, a2)      # self.assertCountEqual(a1, a2)
six.assertRaisesRegex(self, e, r, fn)   # self.assertRaisesRegex(e, r, fn)
six.assertRegex(self, s, r)             # self.assertRegex(s, r)

# input
with io.open('f.txt') as f:
    pass
# output
with open('f.txt') as f:
    pass

# input

# also understands:
# - IOError
# - WindowsError
# - mmap.error and uses of `from mmap import error`
# - select.error and uses of `from select import error`
# - socket.error and uses of `from socket import error`

try:
    raise EnvironmentError('boom')
except EnvironmentError:
    raise
# output
try:
    raise OSError('boom')
except OSError:
    raise

'{foo} {bar}'.format(foo=foo, bar=bar)  # f'{foo} {bar}'
'{} {}'.format(foo, bar)                # f'{foo} {bar}'
'{} {}'.format(foo.bar, baz.womp)       # f'{foo.bar} {baz.womp}'